Add support for compressed PDF streams, using Simon's new deflate library.

[sgt/halibut] / deflate.c

/*
 * Reimplementation of Deflate (RFC1951) compression. Adapted from
 * the version in PuTTY, and extended to write dynamic Huffman
 * trees and choose block boundaries usefully.
 */

/*
 * TODO:
 * 
 *  - Feature: it would probably be useful to add a third format
 *    type to read and write actual gzip files.
 * 
 *  - Feature: the decompress function should return error codes
 *    indicating what kind of thing went wrong in a decoding error
 *    situation, possibly even including a file pointer. I envisage
 *    an enum of error codes in the header file, and one of those
 *    nasty preprocessor tricks to permit a user to define a
 *    code-to-text mapping array.
 *
 *  - Feature: could do with forms of flush other than SYNC_FLUSH.
 *    I'm not sure exactly how those work when you don't know in
 *    advance that your next block will be static (as we did in
 *    PuTTY). And remember the 9-bit limitation of zlib.
 *
 *  - Compression quality: introduce the option of choosing a
 *    static block instead of a dynamic one, where that's more
 *    efficient.
 *
 *  - Compression quality: the actual LZ77 engine appears to be
 *    unable to track a match going beyond the input data passed to
 *    it in a single call. I'd prefer it to be more restartable
 *    than that: we ought to be able to pass in our input data in
 *    whatever size blocks happen to be convenient and not affect
 *    the output at all.
 *
 *  - Compression quality: chooseblock() appears to be computing
 *    wildly inaccurate block size estimates. Possible resolutions:
 *     + find and fix some trivial bug I haven't spotted yet
 *     + abandon the entropic approximation and go with trial
 *       Huffman runs
 *
 *  - Compression quality: see if increasing SYMLIMIT causes
 *    dynamic blocks to start being consistently smaller than it.
 *
 *  - Compression quality: we ought to be able to fall right back
 *    to actual uncompressed blocks if really necessary, though
 *    it's not clear what the criterion for doing so would be.
 *
 *  - Performance: chooseblock() is currently computing the whole
 *    entropic approximation for every possible block size. It
 *    ought to be able to update it incrementally as it goes along
 *    (assuming of course we don't jack it all in and go for a
 *    proper Huffman analysis).
 */

/*
 * This software is copyright 2000-2006 Simon Tatham.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
 * IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <math.h>

#include "deflate.h"

#define snew(type) ( (type *) malloc(sizeof(type)) )
#define snewn(n, type) ( (type *) malloc((n) * sizeof(type)) )
#define sresize(x, n, type) ( (type *) realloc((x), (n) * sizeof(type)) )
#define sfree(x) ( free((x)) )

#define lenof(x) (sizeof((x)) / sizeof(*(x)))

#if defined TESTDBG
/* gcc-specific diagnostic macro */
#define debug_int(x...) ( fprintf(stderr, x) )
#define debug(x) ( debug_int x )
#else
#define debug(x)
#endif

#ifndef FALSE
#define FALSE 0
#define TRUE (!FALSE)
#endif

/* ----------------------------------------------------------------------
 * Basic LZ77 code. This bit is designed modularly, so it could be
 * ripped out and used in a different LZ77 compressor. Go to it,
 * and good luck :-)
 */

struct LZ77InternalContext;
struct LZ77Context {
    struct LZ77InternalContext *ictx;
    void *userdata;
    void (*literal) (struct LZ77Context * ctx, unsigned char c);
    void (*match) (struct LZ77Context * ctx, int distance, int len);
};

/*
 * Initialise the private fields of an LZ77Context. It's up to the
 * user to initialise the public fields.
 */
static int lz77_init(struct LZ77Context *ctx);

/*
 * Supply data to be compressed. Will update the private fields of
 * the LZ77Context, and will call literal() and match() to output.
 * If `compress' is FALSE, it will never emit a match, but will
 * instead call literal() for everything.
 */
static void lz77_compress(struct LZ77Context *ctx,
                          const unsigned char *data, int len, int compress);

/*
 * Modifiable parameters.
 */
#define WINSIZE 32768                  /* window size. Must be power of 2! */
#define HASHMAX 2039                   /* one more than max hash value */
#define MAXMATCH 32                    /* how many matches we track */
#define HASHCHARS 3                    /* how many chars make a hash */

/*
 * This compressor takes a less slapdash approach than the
 * gzip/zlib one. Rather than allowing our hash chains to fall into
 * disuse near the far end, we keep them doubly linked so we can
 * _find_ the far end, and then every time we add a new byte to the
 * window (thus rolling round by one and removing the previous
 * byte), we can carefully remove the hash chain entry.
 */

#define INVALID -1                     /* invalid hash _and_ invalid offset */
struct WindowEntry {
    short next, prev;                  /* array indices within the window */
    short hashval;
};

struct HashEntry {
    short first;                       /* window index of first in chain */
};

struct Match {
    int distance, len;
};

struct LZ77InternalContext {
    struct WindowEntry win[WINSIZE];
    unsigned char data[WINSIZE];
    int winpos;
    struct HashEntry hashtab[HASHMAX];
    unsigned char pending[HASHCHARS];
    int npending;
};

static int lz77_hash(const unsigned char *data)
{
    return (257 * data[0] + 263 * data[1] + 269 * data[2]) % HASHMAX;
}

static int lz77_init(struct LZ77Context *ctx)
{
    struct LZ77InternalContext *st;
    int i;

    st = snew(struct LZ77InternalContext);
    if (!st)
        return 0;

    ctx->ictx = st;

    for (i = 0; i < WINSIZE; i++)
        st->win[i].next = st->win[i].prev = st->win[i].hashval = INVALID;
    for (i = 0; i < HASHMAX; i++)
        st->hashtab[i].first = INVALID;
    st->winpos = 0;

    st->npending = 0;

    return 1;
}

static void lz77_advance(struct LZ77InternalContext *st,
                         unsigned char c, int hash)
{
    int off;

    /*
     * Remove the hash entry at winpos from the tail of its chain,
     * or empty the chain if it's the only thing on the chain.
     */
    if (st->win[st->winpos].prev != INVALID) {
        st->win[st->win[st->winpos].prev].next = INVALID;
    } else if (st->win[st->winpos].hashval != INVALID) {
        st->hashtab[st->win[st->winpos].hashval].first = INVALID;
    }

    /*
     * Create a new entry at winpos and add it to the head of its
     * hash chain.
     */
    st->win[st->winpos].hashval = hash;
    st->win[st->winpos].prev = INVALID;
    off = st->win[st->winpos].next = st->hashtab[hash].first;
    st->hashtab[hash].first = st->winpos;
    if (off != INVALID)
        st->win[off].prev = st->winpos;
    st->data[st->winpos] = c;

    /*
     * Advance the window pointer.
     */
    st->winpos = (st->winpos + 1) & (WINSIZE - 1);
}

#define CHARAT(k) ( (k)<0 ? st->data[(st->winpos+k)&(WINSIZE-1)] : data[k] )

static void lz77_compress(struct LZ77Context *ctx,
                          const unsigned char *data, int len, int compress)
{
    struct LZ77InternalContext *st = ctx->ictx;
    int i, hash, distance, off, nmatch, matchlen, advance;
    struct Match defermatch, matches[MAXMATCH];
    int deferchr;

    /*
     * Add any pending characters from last time to the window. (We
     * might not be able to.)
     */
    for (i = 0; i < st->npending; i++) {
        unsigned char foo[HASHCHARS];
        int j;
        if (len + st->npending - i < HASHCHARS) {
            /* Update the pending array. */
            for (j = i; j < st->npending; j++)
                st->pending[j - i] = st->pending[j];
            break;
        }
        for (j = 0; j < HASHCHARS; j++)
            foo[j] = (i + j < st->npending ? st->pending[i + j] :
                      data[i + j - st->npending]);
        lz77_advance(st, foo[0], lz77_hash(foo));
    }
    st->npending -= i;

    defermatch.len = 0;
    deferchr = '\0';
    while (len > 0) {

        /* Don't even look for a match, if we're not compressing. */
        if (compress && len >= HASHCHARS) {
            /*
             * Hash the next few characters.
             */
            hash = lz77_hash(data);

            /*
             * Look the hash up in the corresponding hash chain and see
             * what we can find.
             */
            nmatch = 0;
            for (off = st->hashtab[hash].first;
                 off != INVALID; off = st->win[off].next) {
                /* distance = 1       if off == st->winpos-1 */
                /* distance = WINSIZE if off == st->winpos   */
                distance =
                    WINSIZE - (off + WINSIZE - st->winpos) % WINSIZE;
                for (i = 0; i < HASHCHARS; i++)
                    if (CHARAT(i) != CHARAT(i - distance))
                        break;
                if (i == HASHCHARS) {
                    matches[nmatch].distance = distance;
                    matches[nmatch].len = 3;
                    if (++nmatch >= MAXMATCH)
                        break;
                }
            }
        } else {
            nmatch = 0;
            hash = INVALID;
        }

        if (nmatch > 0) {
            /*
             * We've now filled up matches[] with nmatch potential
             * matches. Follow them down to find the longest. (We
             * assume here that it's always worth favouring a
             * longer match over a shorter one.)
             */
            matchlen = HASHCHARS;
            while (matchlen < len) {
                int j;
                for (i = j = 0; i < nmatch; i++) {
                    if (CHARAT(matchlen) ==
                        CHARAT(matchlen - matches[i].distance)) {
                        matches[j++] = matches[i];
                    }
                }
                if (j == 0)
                    break;
                matchlen++;
                nmatch = j;
            }

            /*
             * We've now got all the longest matches. We favour the
             * shorter distances, which means we go with matches[0].
             * So see if we want to defer it or throw it away.
             */
            matches[0].len = matchlen;
            if (defermatch.len > 0) {
                if (matches[0].len > defermatch.len + 1) {
                    /* We have a better match. Emit the deferred char,
                     * and defer this match. */
                    ctx->literal(ctx, (unsigned char) deferchr);
                    defermatch = matches[0];
                    deferchr = data[0];
                    advance = 1;
                } else {
                    /* We don't have a better match. Do the deferred one. */
                    ctx->match(ctx, defermatch.distance, defermatch.len);
                    advance = defermatch.len - 1;
                    defermatch.len = 0;
                }
            } else {
                /* There was no deferred match. Defer this one. */
                defermatch = matches[0];
                deferchr = data[0];
                advance = 1;
            }
        } else {
            /*
             * We found no matches. Emit the deferred match, if
             * any; otherwise emit a literal.
             */
            if (defermatch.len > 0) {
                ctx->match(ctx, defermatch.distance, defermatch.len);
                advance = defermatch.len - 1;
                defermatch.len = 0;
            } else {
                ctx->literal(ctx, data[0]);
                advance = 1;
            }
        }

        /*
         * Now advance the position by `advance' characters,
         * keeping the window and hash chains consistent.
         */
        while (advance > 0) {
            if (len >= HASHCHARS) {
                lz77_advance(st, *data, lz77_hash(data));
            } else {
                st->pending[st->npending++] = *data;
            }
            data++;
            len--;
            advance--;
        }
    }
}

/* ----------------------------------------------------------------------
 * Deflate functionality common to both compression and decompression.
 */

static const unsigned char lenlenmap[] = {
    16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
};

#define MAXCODELEN 16

/*
 * Given a sequence of Huffman code lengths, compute the actual
 * codes, in the final form suitable for feeding to outbits (i.e.
 * already bit-mirrored).
 *
 * Returns the maximum code length found.
 */
static int hufcodes(const unsigned char *lengths, int *codes, int nsyms)
{
    int count[MAXCODELEN], startcode[MAXCODELEN];
    int code, maxlen;
    int i, j;

    /* Count the codes of each length. */
    maxlen = 0;
    for (i = 1; i < MAXCODELEN; i++)
        count[i] = 0;
    for (i = 0; i < nsyms; i++) {
        count[lengths[i]]++;
        if (maxlen < lengths[i])
            maxlen = lengths[i];
    }
    /* Determine the starting code for each length block. */
    code = 0;
    for (i = 1; i < MAXCODELEN; i++) {
        startcode[i] = code;
        code += count[i];
        code <<= 1;
    }
    /* Determine the code for each symbol. Mirrored, of course. */
    for (i = 0; i < nsyms; i++) {
        code = startcode[lengths[i]]++;
        codes[i] = 0;
        for (j = 0; j < lengths[i]; j++) {
            codes[i] = (codes[i] << 1) | (code & 1);
            code >>= 1;
        }
    }

    return maxlen;
}

/* ----------------------------------------------------------------------
 * Deflate compression.
 */

#define SYMLIMIT 65536
#define SYMPFX_LITLEN    0x00000000U
#define SYMPFX_DIST      0x40000000U
#define SYMPFX_EXTRABITS 0x80000000U
#define SYMPFX_CODELEN   0xC0000000U
#define SYMPFX_MASK      0xC0000000U

#define SYM_EXTRABITS_MASK 0x3C000000U
#define SYM_EXTRABITS_SHIFT 26

struct deflate_compress_ctx {
    struct LZ77Context *lzc;
    unsigned char *outbuf;
    int outlen, outsize;
    unsigned long outbits;
    int noutbits;
    int firstblock;
    unsigned long *syms;
    int symstart, nsyms;
    int type;
    unsigned long adler32;
    int lastblock;
    int finished;
#ifdef STATISTICS
    unsigned long bitcount;
#endif
};

static void outbits(deflate_compress_ctx *out,
                    unsigned long bits, int nbits)
{
    assert(out->noutbits + nbits <= 32);
    out->outbits |= bits << out->noutbits;
    out->noutbits += nbits;
    while (out->noutbits >= 8) {
        if (out->outlen >= out->outsize) {
            out->outsize = out->outlen + 64;
            out->outbuf = sresize(out->outbuf, out->outsize, unsigned char);
        }
        out->outbuf[out->outlen++] = (unsigned char) (out->outbits & 0xFF);
        out->outbits >>= 8;
        out->noutbits -= 8;
    }
#ifdef STATISTICS
    out->bitcount += nbits;
#endif
}

/*
 * Binary heap functions used by buildhuf(). Each one assumes the
 * heap to be stored in an array of ints, with two ints per node
 * (user data and key). They take in the old heap length, and
 * return the new one.
 */
#define HEAPPARENT(x) (((x)-2)/4*2)
#define HEAPLEFT(x) ((x)*2+2)
#define HEAPRIGHT(x) ((x)*2+4)
static int addheap(int *heap, int len, int userdata, int key)
{
    int me, dad, tmp;

    me = len;
    heap[len++] = userdata;
    heap[len++] = key;

    while (me > 0) {
        dad = HEAPPARENT(me);
        if (heap[me+1] < heap[dad+1]) {
            tmp = heap[me]; heap[me] = heap[dad]; heap[dad] = tmp;
            tmp = heap[me+1]; heap[me+1] = heap[dad+1]; heap[dad+1] = tmp;
            me = dad;
        } else
            break;
    }

    return len;
}
static int rmheap(int *heap, int len, int *userdata, int *key)
{
    int me, lc, rc, c, tmp;

    len -= 2;
    *userdata = heap[0];
    *key = heap[1];
    heap[0] = heap[len];
    heap[1] = heap[len+1];

    me = 0;

    while (1) {
        lc = HEAPLEFT(me);
        rc = HEAPRIGHT(me);
        if (lc >= len)
            break;
        else if (rc >= len || heap[lc+1] < heap[rc+1])
            c = lc;
        else
            c = rc;
        if (heap[me+1] > heap[c+1]) {
            tmp = heap[me]; heap[me] = heap[c]; heap[c] = tmp;
            tmp = heap[me+1]; heap[me+1] = heap[c+1]; heap[c+1] = tmp;
        } else
            break;
        me = c;
    }

    return len;
}

/*
 * The core of the Huffman algorithm: takes an input array of
 * symbol frequencies, and produces an output array of code
 * lengths.
 *
 * This is basically a generic Huffman implementation, but it has
 * one zlib-related quirk which is that it caps the output code
 * lengths to fit in an unsigned char (which is safe since Deflate
 * will reject anything longer than 15 anyway). Anyone wanting to
 * rip it out and use it in another context should find that easy
 * to remove.
 */
#define HUFMAX 286
static void buildhuf(const int *freqs, unsigned char *lengths, int nsyms)
{
    int parent[2*HUFMAX-1];
    int length[2*HUFMAX-1];
    int heap[2*HUFMAX];
    int heapsize;
    int i, j, n;
    int si, sj;

    assert(nsyms <= HUFMAX);

    memset(parent, 0, sizeof(parent));

    /*
     * Begin by building the heap.
     */
    heapsize = 0;
    for (i = 0; i < nsyms; i++)
        if (freqs[i] > 0)              /* leave unused symbols out totally */
            heapsize = addheap(heap, heapsize, i, freqs[i]);

    /*
     * Now repeatedly take two elements off the heap and merge
     * them.
     */
    n = HUFMAX;
    while (heapsize > 2) {
        heapsize = rmheap(heap, heapsize, &i, &si);
        heapsize = rmheap(heap, heapsize, &j, &sj);
        parent[i] = n;
        parent[j] = n;
        heapsize = addheap(heap, heapsize, n, si + sj);
        n++;
    }

    /*
     * Now we have our tree, in the form of a link from each node
     * to the index of its parent. Count back down the tree to
     * determine the code lengths.
     */
    memset(length, 0, sizeof(length));
    /* The tree root has length 0 after that, which is correct. */
    for (i = n-1; i-- ;)
        if (parent[i] > 0)
            length[i] = 1 + length[parent[i]];

    /*
     * And that's it. (Simple, wasn't it?) Copy the lengths into
     * the output array and leave.
     * 
     * Here we cap lengths to fit in unsigned char.
     */
    for (i = 0; i < nsyms; i++)
        lengths[i] = (length[i] > 255 ? 255 : length[i]);
}

/*
 * Wrapper around buildhuf() which enforces the Deflate restriction
 * that no code length may exceed 15 bits, or 7 for the auxiliary
 * code length alphabet. This function has the same calling
 * semantics as buildhuf(), except that it might modify the freqs
 * array.
 */
static void deflate_buildhuf(int *freqs, unsigned char *lengths,
                             int nsyms, int limit)
{
    int smallestfreq, totalfreq, nactivesyms;
    int num, denom, adjust;
    int i;
    int maxprob;

    /*
     * First, try building the Huffman table the normal way. If
     * this works, it's optimal, so we don't want to mess with it.
     */
    buildhuf(freqs, lengths, nsyms);

    for (i = 0; i < nsyms; i++)
        if (lengths[i] > limit)
            break;

    if (i == nsyms)
        return;                        /* OK */

    /*
     * The Huffman algorithm can only ever generate a code length
     * of N bits or more if there is a symbol whose probability is
     * less than the reciprocal of the (N+2)th Fibonacci number
     * (counting from F_0=0 and F_1=1), i.e. 1/2584 for N=16, or
     * 1/55 for N=8. (This is a necessary though not sufficient
     * condition.)
     *
     * Why is this? Well, consider the input symbol with the
     * smallest probability. Let that probability be x. In order
     * for this symbol to have a code length of at least 1, the
     * Huffman algorithm will have to merge it with some other
     * node; and since x is the smallest probability, the node it
     * gets merged with must be at least x. Thus, the probability
     * of the resulting combined node will be at least 2x. Now in
     * order for our node to reach depth 2, this 2x-node must be
     * merged again. But what with? We can't assume the node it
     * merges with is at least 2x, because this one might only be
     * the _second_ smallest remaining node. But we do know the
     * node it merges with must be at least x, so our order-2
     * internal node is at least 3x.
     *
     * How small a node can merge with _that_ to get an order-3
     * internal node? Well, it must be at least 2x, because if it
     * was smaller than that then it would have been one of the two
     * smallest nodes in the previous step and been merged at that
     * point. So at least 3x, plus at least 2x, comes to at least
     * 5x for an order-3 node.
     *
     * And so it goes on: at every stage we must merge our current
     * node with a node at least as big as the bigger of this one's
     * two parents, and from this starting point that gives rise to
     * the Fibonacci sequence. So we find that in order to have a
     * node n levels deep (i.e. a maximum code length of n), the
     * overall probability of the root of the entire tree must be
     * at least F_{n+2} times the probability of the rarest symbol.
     * In other words, since the overall probability is 1, it is a
     * necessary condition for a code length of 16 or more that
     * there must be at least one symbol with probability <=
     * 1/F_18.
     *
     * (To demonstrate that a probability this big really can give
     * rise to a code length of 16, consider the set of input
     * frequencies { 1-epsilon, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55,
     * 89, 144, 233, 377, 610, 987 }, for arbitrarily small
     * epsilon.)
     *
     * So here buildhuf() has returned us an overlong code. So to
     * ensure it doesn't do it again, we add a constant to all the
     * (non-zero) symbol frequencies, causing them to become more
     * balanced and removing the danger. We can then feed the
     * results back to the standard buildhuf() and be
     * assert()-level confident that the resulting code lengths
     * contain nothing outside the permitted range.
     */
    maxprob = (limit == 16 ? 2584 : 55);   /* no point in computing full F_n */
    totalfreq = nactivesyms = 0;
    smallestfreq = -1;
    for (i = 0; i < nsyms; i++) {
        if (freqs[i] == 0)
            continue;
        if (smallestfreq < 0 || smallestfreq > freqs[i])
            smallestfreq = freqs[i];
        totalfreq += freqs[i];
        nactivesyms++;
    }
    assert(smallestfreq <= totalfreq / maxprob);

    /*
     * We want to find the smallest integer `adjust' such that
     * (totalfreq + nactivesyms * adjust) / (smallestfreq +
     * adjust) is less than maxprob. A bit of algebra tells us
     * that the threshold value is equal to
     *
     *   totalfreq - maxprob * smallestfreq
     *   ----------------------------------
     *          maxprob - nactivesyms
     *
     * rounded up, of course. And we'll only even be trying
     * this if
     */
    num = totalfreq - smallestfreq * maxprob;
    denom = maxprob - nactivesyms;
    adjust = (num + denom - 1) / denom;

    /*
     * Now add `adjust' to all the input symbol frequencies.
     */
    for (i = 0; i < nsyms; i++)
        if (freqs[i] != 0)
            freqs[i] += adjust;

    /*
     * Rebuild the Huffman tree...
     */
    buildhuf(freqs, lengths, nsyms);

    /*
     * ... and this time it ought to be OK.
     */
    for (i = 0; i < nsyms; i++)
        assert(lengths[i] <= limit);
}

struct huftrees {
    unsigned char *len_litlen;
    int *code_litlen;
    unsigned char *len_dist;
    int *code_dist;
    unsigned char *len_codelen;
    int *code_codelen;
};

/*
 * Write out a single symbol, given the three Huffman trees.
 */
static void writesym(deflate_compress_ctx *out,
                     unsigned sym, struct huftrees *trees)
{
    unsigned basesym = sym &~ SYMPFX_MASK;
    int i;

    switch (sym & SYMPFX_MASK) {
      case SYMPFX_LITLEN:
        debug(("send: litlen %d\n", basesym));
        outbits(out, trees->code_litlen[basesym], trees->len_litlen[basesym]);
        break;
      case SYMPFX_DIST:
        debug(("send: dist %d\n", basesym));
        outbits(out, trees->code_dist[basesym], trees->len_dist[basesym]);
        break;
      case SYMPFX_CODELEN:
        debug(("send: codelen %d\n", basesym));
        outbits(out, trees->code_codelen[basesym],trees->len_codelen[basesym]);
        break;
      case SYMPFX_EXTRABITS:
        i = basesym >> SYM_EXTRABITS_SHIFT;
        basesym &= ~SYM_EXTRABITS_MASK;
        debug(("send: extrabits %d/%d\n", basesym, i));
        outbits(out, basesym, i);
        break;
    }
}

static void outblock(deflate_compress_ctx *out,
                     int blklen, int dynamic)
{
    int freqs1[286], freqs2[30], freqs3[19];
    unsigned char len1[286], len2[30], len3[19];
    int code1[286], code2[30], code3[19];
    int hlit, hdist, hclen, bfinal, btype;
    int treesrc[286 + 30];
    int treesyms[286 + 30];
    int codelen[19];
    int i, ntreesrc, ntreesyms;
    struct huftrees ht;
#ifdef STATISTICS
    unsigned long bitcount_before;
#endif

    ht.len_litlen = len1;
    ht.len_dist = len2;
    ht.len_codelen = len3;
    ht.code_litlen = code1;
    ht.code_dist = code2;
    ht.code_codelen = code3;

    /*
     * Build the two main Huffman trees.
     */
    if (dynamic) {
        /*
         * Count up the frequency tables.
         */
        memset(freqs1, 0, sizeof(freqs1));
        memset(freqs2, 0, sizeof(freqs2));
        freqs1[256] = 1;               /* we're bound to need one EOB */
        for (i = 0; i < blklen; i++) {
            unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];

            /*
             * Increment the occurrence counter for this symbol, if
             * it's in one of the Huffman alphabets and isn't extra
             * bits.
             */
            if ((sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
                sym &= ~SYMPFX_MASK;
                assert(sym < lenof(freqs1));
                freqs1[sym]++;
            } else if ((sym & SYMPFX_MASK) == SYMPFX_DIST) {
                sym &= ~SYMPFX_MASK;
                assert(sym < lenof(freqs2));
                freqs2[sym]++;
            }
        }
        deflate_buildhuf(freqs1, len1, lenof(freqs1), 15);
        deflate_buildhuf(freqs2, len2, lenof(freqs2), 15);
    } else {
        /*
         * Fixed static trees.
         */
        for (i = 0; i < lenof(len1); i++)
            len1[i] = (i < 144 ? 8 :
                       i < 256 ? 9 :
                       i < 280 ? 7 : 8);
        for (i = 0; i < lenof(len2); i++)
            len2[i] = 5;
    }
    hufcodes(len1, code1, lenof(freqs1));
    hufcodes(len2, code2, lenof(freqs2));

    if (dynamic) {
        /*
         * Determine HLIT and HDIST.
         */
        for (hlit = 286; hlit > 257 && len1[hlit-1] == 0; hlit--);
        for (hdist = 30; hdist > 1 && len2[hdist-1] == 0; hdist--);

        /*
         * Write out the list of symbols used to transmit the
         * trees.
         */
        ntreesrc = 0;
        for (i = 0; i < hlit; i++)
            treesrc[ntreesrc++] = len1[i];
        for (i = 0; i < hdist; i++)
            treesrc[ntreesrc++] = len2[i];
        ntreesyms = 0;
        for (i = 0; i < ntreesrc ;) {
            int j = 1;
            int k;

            /* Find length of run of the same length code. */
            while (i+j < ntreesrc && treesrc[i+j] == treesrc[i])
                j++;

            /* Encode that run as economically as we can. */
            k = j;
            if (treesrc[i] == 0) {
                /*
                 * Zero code length: we can output run codes for
                 * 3-138 zeroes. So if we have fewer than 3 zeroes,
                 * we just output literals. Otherwise, we output
                 * nothing but run codes, and tweak their lengths
                 * to make sure we aren't left with under 3 at the
                 * end.
                 */
                if (k < 3) {
                    while (k--)
                        treesyms[ntreesyms++] = 0 | SYMPFX_CODELEN;
                } else {
                    while (k > 0) {
                        int rpt = (k < 138 ? k : 138);
                        if (rpt > k-3 && rpt < k)
                            rpt = k-3;
                        assert(rpt >= 3 && rpt <= 138);
                        if (rpt < 11) {
                            treesyms[ntreesyms++] = 17 | SYMPFX_CODELEN;
                            treesyms[ntreesyms++] =
                                (SYMPFX_EXTRABITS | (rpt - 3) |
                                 (3 << SYM_EXTRABITS_SHIFT));
                        } else {
                            treesyms[ntreesyms++] = 18 | SYMPFX_CODELEN;
                            treesyms[ntreesyms++] =
                                (SYMPFX_EXTRABITS | (rpt - 11) |
                                 (7 << SYM_EXTRABITS_SHIFT));
                        }
                        k -= rpt;
                    }
                }
            } else {
                /*
                 * Non-zero code length: we must output the first
                 * one explicitly, then we can output a copy code
                 * for 3-6 repeats. So if we have fewer than 4
                 * repeats, we _just_ output literals. Otherwise,
                 * we output one literal plus at least one copy
                 * code, and tweak the copy codes to make sure we
                 * aren't left with under 3 at the end.
                 */
                assert(treesrc[i] < 16);
                treesyms[ntreesyms++] = treesrc[i] | SYMPFX_CODELEN;
                k--;
                if (k < 3) {
                    while (k--)
                        treesyms[ntreesyms++] = treesrc[i] | SYMPFX_CODELEN;
                } else {
                    while (k > 0) {
                        int rpt = (k < 6 ? k : 6);
                        if (rpt > k-3 && rpt < k)
                            rpt = k-3;
                        assert(rpt >= 3 && rpt <= 6);
                        treesyms[ntreesyms++] = 16 | SYMPFX_CODELEN;
                        treesyms[ntreesyms++] = (SYMPFX_EXTRABITS | (rpt - 3) |
                                                 (2 << SYM_EXTRABITS_SHIFT));
                        k -= rpt;
                    }
                }
            }

            i += j;
        }
        assert((unsigned)ntreesyms < lenof(treesyms));

        /*
         * Count up the frequency table for the tree-transmission
         * symbols, and build the auxiliary Huffman tree for that.
         */
        memset(freqs3, 0, sizeof(freqs3));
        for (i = 0; i < ntreesyms; i++) {
            unsigned sym = treesyms[i];

            /*
             * Increment the occurrence counter for this symbol, if
             * it's the Huffman alphabet and isn't extra bits.
             */
            if ((sym & SYMPFX_MASK) == SYMPFX_CODELEN) {
                sym &= ~SYMPFX_MASK;
                assert(sym < lenof(freqs3));
                freqs3[sym]++;
            }
        }
        deflate_buildhuf(freqs3, len3, lenof(freqs3), 7);
        hufcodes(len3, code3, lenof(freqs3));

        /*
         * Reorder the code length codes into transmission order, and
         * determine HCLEN.
         */
        for (i = 0; i < 19; i++)
            codelen[i] = len3[lenlenmap[i]];
        for (hclen = 19; hclen > 4 && codelen[hclen-1] == 0; hclen--);
    }

    /*
     * Actually transmit the block.
     */

    /* 3-bit block header */
    bfinal = (out->lastblock ? 1 : 0);
    btype = dynamic ? 2 : 1;
    debug(("send: bfinal=%d btype=%d\n", bfinal, btype));
    outbits(out, bfinal, 1);
    outbits(out, btype, 2);

#ifdef STATISTICS
    bitcount_before = out->bitcount;
#endif

    if (dynamic) {
        /* HLIT, HDIST and HCLEN */
        debug(("send: hlit=%d hdist=%d hclen=%d\n", hlit, hdist, hclen));
        outbits(out, hlit - 257, 5);
        outbits(out, hdist - 1, 5);
        outbits(out, hclen - 4, 4);

        /* Code lengths for the auxiliary tree */
        for (i = 0; i < hclen; i++) {
            debug(("send: lenlen %d\n", codelen[i]));
            outbits(out, codelen[i], 3);
        }

        /* Code lengths for the literal/length and distance trees */
        for (i = 0; i < ntreesyms; i++)
            writesym(out, treesyms[i], &ht);
#ifdef STATISTICS
        fprintf(stderr, "total tree size %lu bits\n",
                out->bitcount - bitcount_before);
#endif
    }

    /* Output the actual symbols from the buffer */
    for (i = 0; i < blklen; i++) {
        unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
        writesym(out, sym, &ht);
    }

    /* Output the end-of-data symbol */
    writesym(out, SYMPFX_LITLEN | 256, &ht);

    /*
     * Remove all the just-output symbols from the symbol buffer by
     * adjusting symstart and nsyms.
     */
    out->symstart = (out->symstart + blklen) % SYMLIMIT;
    out->nsyms -= blklen;
}

static void outblock_wrapper(deflate_compress_ctx *out,
                             int best_dynamic_len)
{
    /*
     * Final block choice function: we have the option of either
     * outputting a dynamic block of length best_dynamic_len, or a
     * static block of length out->nsyms. Whichever gives us the
     * best value for money, we do.
     *
     * FIXME: currently we always choose dynamic except for empty
     * blocks. We should make a sensible judgment.
     */
    if (out->nsyms == 0)
        outblock(out, 0, FALSE);
    else
        outblock(out, best_dynamic_len, TRUE);
}

static void chooseblock(deflate_compress_ctx *out)
{
    int freqs1[286], freqs2[30];
    int i, bestlen;
    double bestvfm;
    int nextrabits;

    memset(freqs1, 0, sizeof(freqs1));
    memset(freqs2, 0, sizeof(freqs2));
    freqs1[256] = 1;                   /* we're bound to need one EOB */
    nextrabits = 0;

    /*
     * Iterate over all possible block lengths, computing the
     * entropic coding approximation to the final length at every
     * stage. We divide the result by the number of symbols
     * encoded, to determine the `value for money' (overall
     * bits-per-symbol count) of a block of that length.
     */
    bestlen = -1;
    bestvfm = 0.0;
    for (i = 0; i < out->nsyms; i++) {
        unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];

        if (i > 0 && (sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
            /*
             * This is a viable point at which to end the block.
             * Compute the length approximation and hence the value
             * for money.
             */
            double len = 0.0, vfm;
            int k;
            int total;

            /*
             * FIXME: we should be doing this incrementally, rather
             * than recomputing the whole thing at every byte
             * position. Also, can we fiddle the logs somehow to
             * avoid having to do floating point?
             */
            total = 0;
            for (k = 0; k < (int)lenof(freqs1); k++) {
                if (freqs1[k])
                    len -= freqs1[k] * log(freqs1[k]);
                total += freqs1[k];
            }
            if (total)
                len += total * log(total);
            total = 0;
            for (k = 0; k < (int)lenof(freqs2); k++) {
                if (freqs2[k])
                    len -= freqs2[k] * log(freqs2[k]);
                total += freqs2[k];
            }
            if (total)
                len += total * log(total);
            len /= log(2);
            len += nextrabits;
            len += 300;   /* very approximate size of the Huffman trees */

            vfm = i / len;             /* symbols encoded per bit */
/* fprintf(stderr, "chooseblock: i=%d gives len %g, vfm %g\n", i, len, vfm); */
            if (bestlen < 0 || vfm > bestvfm) {
                bestlen = i;
                bestvfm = vfm;
            }
        }

        /*
         * Increment the occurrence counter for this symbol, if
         * it's in one of the Huffman alphabets and isn't extra
         * bits.
         */
        if ((sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
            sym &= ~SYMPFX_MASK;
            assert(sym < lenof(freqs1));
            freqs1[sym]++;
        } else if ((sym & SYMPFX_MASK) == SYMPFX_DIST) {
            sym &= ~SYMPFX_MASK;
            assert(sym < lenof(freqs2));
            freqs2[sym]++;
        } else if ((sym & SYMPFX_MASK) == SYMPFX_EXTRABITS) {
            nextrabits += (sym &~ SYMPFX_MASK) >> SYM_EXTRABITS_SHIFT;
        }
    }

    assert(bestlen > 0);

/* fprintf(stderr, "chooseblock: bestlen %d, bestvfm %g\n", bestlen, bestvfm); */
    outblock_wrapper(out, bestlen);
}

/*
 * Force the current symbol buffer to be flushed out as a single
 * block.
 */
static void flushblock(deflate_compress_ctx *out)
{
    /*
     * Because outblock_wrapper guarantees to output either a
     * dynamic block of the given length or a static block of
     * length out->nsyms, we know that passing out->nsyms as the
     * given length will definitely result in us using up the
     * entire buffer.
     */
    outblock_wrapper(out, out->nsyms);
    assert(out->nsyms == 0);
}

/*
 * Place a symbol into the symbols buffer.
 */
static void outsym(deflate_compress_ctx *out, unsigned long sym)
{
    assert(out->nsyms < SYMLIMIT);
    out->syms[(out->symstart + out->nsyms++) % SYMLIMIT] = sym;

    if (out->nsyms == SYMLIMIT)
        chooseblock(out);
}

typedef struct {
    short code, extrabits;
    int min, max;
} coderecord;

static const coderecord lencodes[] = {
    {257, 0, 3, 3},
    {258, 0, 4, 4},
    {259, 0, 5, 5},
    {260, 0, 6, 6},
    {261, 0, 7, 7},
    {262, 0, 8, 8},
    {263, 0, 9, 9},
    {264, 0, 10, 10},
    {265, 1, 11, 12},
    {266, 1, 13, 14},
    {267, 1, 15, 16},
    {268, 1, 17, 18},
    {269, 2, 19, 22},
    {270, 2, 23, 26},
    {271, 2, 27, 30},
    {272, 2, 31, 34},
    {273, 3, 35, 42},
    {274, 3, 43, 50},
    {275, 3, 51, 58},
    {276, 3, 59, 66},
    {277, 4, 67, 82},
    {278, 4, 83, 98},
    {279, 4, 99, 114},
    {280, 4, 115, 130},
    {281, 5, 131, 162},
    {282, 5, 163, 194},
    {283, 5, 195, 226},
    {284, 5, 227, 257},
    {285, 0, 258, 258},
};

static const coderecord distcodes[] = {
    {0, 0, 1, 1},
    {1, 0, 2, 2},
    {2, 0, 3, 3},
    {3, 0, 4, 4},
    {4, 1, 5, 6},
    {5, 1, 7, 8},
    {6, 2, 9, 12},
    {7, 2, 13, 16},
    {8, 3, 17, 24},
    {9, 3, 25, 32},
    {10, 4, 33, 48},
    {11, 4, 49, 64},
    {12, 5, 65, 96},
    {13, 5, 97, 128},
    {14, 6, 129, 192},
    {15, 6, 193, 256},
    {16, 7, 257, 384},
    {17, 7, 385, 512},
    {18, 8, 513, 768},
    {19, 8, 769, 1024},
    {20, 9, 1025, 1536},
    {21, 9, 1537, 2048},
    {22, 10, 2049, 3072},
    {23, 10, 3073, 4096},
    {24, 11, 4097, 6144},
    {25, 11, 6145, 8192},
    {26, 12, 8193, 12288},
    {27, 12, 12289, 16384},
    {28, 13, 16385, 24576},
    {29, 13, 24577, 32768},
};

static void literal(struct LZ77Context *ectx, unsigned char c)
{
    deflate_compress_ctx *out = (deflate_compress_ctx *) ectx->userdata;

    outsym(out, SYMPFX_LITLEN | c);
}

static void match(struct LZ77Context *ectx, int distance, int len)
{
    const coderecord *d, *l;
    int i, j, k;
    deflate_compress_ctx *out = (deflate_compress_ctx *) ectx->userdata;

    while (len > 0) {
        int thislen;

        /*
         * We can transmit matches of lengths 3 through 258
         * inclusive. So if len exceeds 258, we must transmit in
         * several steps, with 258 or less in each step.
         *
         * Specifically: if len >= 261, we can transmit 258 and be
         * sure of having at least 3 left for the next step. And if
         * len <= 258, we can just transmit len. But if len == 259
         * or 260, we must transmit len-3.
         */
        thislen = (len > 260 ? 258 : len <= 258 ? len : len - 3);
        len -= thislen;

        /*
         * Binary-search to find which length code we're
         * transmitting.
         */
        i = -1;
        j = sizeof(lencodes) / sizeof(*lencodes);
        while (1) {
            assert(j - i >= 2);
            k = (j + i) / 2;
            if (thislen < lencodes[k].min)
                j = k;
            else if (thislen > lencodes[k].max)
                i = k;
            else {
                l = &lencodes[k];
                break;                 /* found it! */
            }
        }

        /*
         * Transmit the length code.
         */
        outsym(out, SYMPFX_LITLEN | l->code);

        /*
         * Transmit the extra bits.
         */
        if (l->extrabits) {
            outsym(out, (SYMPFX_EXTRABITS | (thislen - l->min) |
                         (l->extrabits << SYM_EXTRABITS_SHIFT)));
        }

        /*
         * Binary-search to find which distance code we're
         * transmitting.
         */
        i = -1;
        j = sizeof(distcodes) / sizeof(*distcodes);
        while (1) {
            assert(j - i >= 2);
            k = (j + i) / 2;
            if (distance < distcodes[k].min)
                j = k;
            else if (distance > distcodes[k].max)
                i = k;
            else {
                d = &distcodes[k];
                break;                 /* found it! */
            }
        }

        /*
         * Write the distance code.
         */
        outsym(out, SYMPFX_DIST | d->code);

        /*
         * Transmit the extra bits.
         */
        if (d->extrabits) {
            outsym(out, (SYMPFX_EXTRABITS | (distance - d->min) |
                         (d->extrabits << SYM_EXTRABITS_SHIFT)));
        }
    }
}

deflate_compress_ctx *deflate_compress_new(int type)
{
    deflate_compress_ctx *out;
    struct LZ77Context *ectx = snew(struct LZ77Context);

    lz77_init(ectx);
    ectx->literal = literal;
    ectx->match = match;

    out = snew(deflate_compress_ctx);
    out->type = type;
    out->outbits = out->noutbits = 0;
    out->firstblock = TRUE;
#ifdef STATISTICS
    out->bitcount = 0;
#endif

    out->syms = snewn(SYMLIMIT, unsigned long);
    out->symstart = out->nsyms = 0;

    out->adler32 = 1;
    out->lastblock = FALSE;
    out->finished = FALSE;

    ectx->userdata = out;
    out->lzc = ectx;

    return out;
}

void deflate_compress_free(deflate_compress_ctx *out)
{
    struct LZ77Context *ectx = out->lzc;

    sfree(out->syms);
    sfree(out);
    sfree(ectx->ictx);
    sfree(ectx);
}

static unsigned long adler32_update(unsigned long s,
                                    const unsigned char *data, int len)
{
    unsigned s1 = s & 0xFFFF, s2 = (s >> 16) & 0xFFFF;
    int i;

    for (i = 0; i < len; i++) {
        s1 += data[i];
        s2 += s1;
        if (!(i & 0xFFF)) {
            s1 %= 65521;
            s2 %= 65521;
        }
    }

    return ((s2 % 65521) << 16) | (s1 % 65521);
}

int deflate_compress_data(deflate_compress_ctx *out,
                          const void *vblock, int len, int flushtype,
                          void **outblock, int *outlen)
{
    struct LZ77Context *ectx = out->lzc;
    const unsigned char *block = (const unsigned char *)vblock;

    assert(!out->finished);

    out->outbuf = NULL;
    out->outlen = out->outsize = 0;

    /*
     * If this is the first block, output the header.
     */
    if (out->firstblock) {
        switch (out->type) {
          case DEFLATE_TYPE_BARE:
            break;                     /* no header */
          case DEFLATE_TYPE_ZLIB:
            /*
             * Zlib (RFC1950) header bytes: 78 9C. (Deflate
             * compression, 32K window size, default algorithm.)
             */
            outbits(out, 0x9C78, 16);
            break;
        }
        out->firstblock = FALSE;
    }

    /*
     * Feed our data to the LZ77 compression phase.
     */
    lz77_compress(ectx, block, len, TRUE);

    /*
     * Update checksums.
     */
    if (out->type == DEFLATE_TYPE_ZLIB)
        out->adler32 = adler32_update(out->adler32, block, len);

    switch (flushtype) {
        /*
         * FIXME: what other flush types are available and useful?
         * In PuTTY, it was clear that we generally wanted to be in
         * a static block so it was safe to open one. Here, we
         * probably prefer to be _outside_ a block if we can. Think
         * about this.
         */
      case DEFLATE_NO_FLUSH:
        break;                         /* don't flush any data at all (duh) */
      case DEFLATE_SYNC_FLUSH:
        /*
         * Close the current block.
         */
        flushblock(out);

        /*
         * Then output an empty _uncompressed_ block: send 000,
         * then sync to byte boundary, then send bytes 00 00 FF
         * FF.
         */
        outbits(out, 0, 3);
        if (out->noutbits)
            outbits(out, 0, 8 - out->noutbits);
        outbits(out, 0, 16);
        outbits(out, 0xFFFF, 16);
        break;
      case DEFLATE_END_OF_DATA:
        /*
         * Output a block with BFINAL set.
         */
        out->lastblock = TRUE;
        flushblock(out);

        /*
         * Sync to byte boundary, flushing out the final byte.
         */
        if (out->noutbits)
            outbits(out, 0, 8 - out->noutbits);

        /*
         * Output the adler32 checksum, in zlib mode.
         */
        if (out->type == DEFLATE_TYPE_ZLIB) {
            outbits(out, (out->adler32 >> 24) & 0xFF, 8);
            outbits(out, (out->adler32 >> 16) & 0xFF, 8);
            outbits(out, (out->adler32 >>  8) & 0xFF, 8);
            outbits(out, (out->adler32 >>  0) & 0xFF, 8);
        }

        out->finished = TRUE;
        break;
    }

    /*
     * Return any data that we've generated.
     */
    *outblock = (void *)out->outbuf;
    *outlen = out->outlen;

    return 1;
}

/* ----------------------------------------------------------------------
 * deflate decompression.
 */

/*
 * The way we work the Huffman decode is to have a table lookup on
 * the first N bits of the input stream (in the order they arrive,
 * of course, i.e. the first bit of the Huffman code is in bit 0).
 * Each table entry lists the number of bits to consume, plus
 * either an output code or a pointer to a secondary table.
 */
struct table;
struct tableentry;

struct tableentry {
    unsigned char nbits;
    short code;
    struct table *nexttable;
};

struct table {
    int mask;                          /* mask applied to input bit stream */
    struct tableentry *table;
};

#define MAXSYMS 288

/*
 * Build a single-level decode table for elements
 * [minlength,maxlength) of the provided code/length tables, and
 * recurse to build subtables.
 */
static struct table *mkonetab(int *codes, unsigned char *lengths, int nsyms,
                              int pfx, int pfxbits, int bits)
{
    struct table *tab = snew(struct table);
    int pfxmask = (1 << pfxbits) - 1;
    int nbits, i, j, code;

    tab->table = snewn(1 << bits, struct tableentry);
    tab->mask = (1 << bits) - 1;

    for (code = 0; code <= tab->mask; code++) {
        tab->table[code].code = -1;
        tab->table[code].nbits = 0;
        tab->table[code].nexttable = NULL;
    }

    for (i = 0; i < nsyms; i++) {
        if (lengths[i] <= pfxbits || (codes[i] & pfxmask) != pfx)
            continue;
        code = (codes[i] >> pfxbits) & tab->mask;
        for (j = code; j <= tab->mask; j += 1 << (lengths[i] - pfxbits)) {
            tab->table[j].code = i;
            nbits = lengths[i] - pfxbits;
            if (tab->table[j].nbits < nbits)
                tab->table[j].nbits = nbits;
        }
    }
    for (code = 0; code <= tab->mask; code++) {
        if (tab->table[code].nbits <= bits)
            continue;
        /* Generate a subtable. */
        tab->table[code].code = -1;
        nbits = tab->table[code].nbits - bits;
        if (nbits > 7)
            nbits = 7;
        tab->table[code].nbits = bits;
        tab->table[code].nexttable = mkonetab(codes, lengths, nsyms,
                                              pfx | (code << pfxbits),
                                              pfxbits + bits, nbits);
    }

    return tab;
}

/*
 * Build a decode table, given a set of Huffman tree lengths.
 */
static struct table *mktable(unsigned char *lengths, int nlengths)
{
    int codes[MAXSYMS];
    int maxlen;

    maxlen = hufcodes(lengths, codes, nlengths);

    /*
     * Now we have the complete list of Huffman codes. Build a
     * table.
     */
    return mkonetab(codes, lengths, nlengths, 0, 0, maxlen < 9 ? maxlen : 9);
}

static int freetable(struct table **ztab)
{
    struct table *tab;
    int code;

    if (ztab == NULL)
        return -1;

    if (*ztab == NULL)
        return 0;

    tab = *ztab;

    for (code = 0; code <= tab->mask; code++)
        if (tab->table[code].nexttable != NULL)
            freetable(&tab->table[code].nexttable);

    sfree(tab->table);
    tab->table = NULL;

    sfree(tab);
    *ztab = NULL;

    return (0);
}

struct deflate_decompress_ctx {
    struct table *staticlentable, *staticdisttable;
    struct table *currlentable, *currdisttable, *lenlentable;
    enum {
        START, OUTSIDEBLK,
        TREES_HDR, TREES_LENLEN, TREES_LEN, TREES_LENREP,
        INBLK, GOTLENSYM, GOTLEN, GOTDISTSYM,
        UNCOMP_LEN, UNCOMP_NLEN, UNCOMP_DATA,
        END, ADLER1, ADLER2, FINALSPIN
    } state;
    int sym, hlit, hdist, hclen, lenptr, lenextrabits, lenaddon, len,
        lenrep, lastblock;
    int uncomplen;
    unsigned char lenlen[19];
    unsigned char lengths[286 + 32];
    unsigned long bits;
    int nbits;
    unsigned char window[WINSIZE];
    int winpos;
    unsigned char *outblk;
    int outlen, outsize;
    int type;
    unsigned long adler32;
};

deflate_decompress_ctx *deflate_decompress_new(int type)
{
    deflate_decompress_ctx *dctx = snew(deflate_decompress_ctx);
    unsigned char lengths[288];

    memset(lengths, 8, 144);
    memset(lengths + 144, 9, 256 - 144);
    memset(lengths + 256, 7, 280 - 256);
    memset(lengths + 280, 8, 288 - 280);
    dctx->staticlentable = mktable(lengths, 288);
    memset(lengths, 5, 32);
    dctx->staticdisttable = mktable(lengths, 32);
    if (type == DEFLATE_TYPE_BARE)
        dctx->state = OUTSIDEBLK;
    else
        dctx->state = START;
    dctx->currlentable = dctx->currdisttable = dctx->lenlentable = NULL;
    dctx->bits = 0;
    dctx->nbits = 0;
    dctx->winpos = 0;
    dctx->type = type;
    dctx->lastblock = FALSE;
    dctx->adler32 = 1;

    return dctx;
}

void deflate_decompress_free(deflate_decompress_ctx *dctx)
{
    if (dctx->currlentable && dctx->currlentable != dctx->staticlentable)
        freetable(&dctx->currlentable);
    if (dctx->currdisttable && dctx->currdisttable != dctx->staticdisttable)
        freetable(&dctx->currdisttable);
    if (dctx->lenlentable)
        freetable(&dctx->lenlentable);
    freetable(&dctx->staticlentable);
    freetable(&dctx->staticdisttable);
    sfree(dctx);
}

static int huflookup(unsigned long *bitsp, int *nbitsp, struct table *tab)
{
    unsigned long bits = *bitsp;
    int nbits = *nbitsp;
    while (1) {
        struct tableentry *ent;
        ent = &tab->table[bits & tab->mask];
        if (ent->nbits > nbits)
            return -1;                 /* not enough data */
        bits >>= ent->nbits;
        nbits -= ent->nbits;
        if (ent->code == -1)
            tab = ent->nexttable;
        else {
            *bitsp = bits;
            *nbitsp = nbits;
            return ent->code;
        }

        if (!tab) {
            /*
             * There was a missing entry in the table, presumably
             * due to an invalid Huffman table description, and the
             * subsequent data has attempted to use the missing
             * entry. Return a decoding failure.
             */
            return -2;
        }
    }
}

static void emit_char(deflate_decompress_ctx *dctx, int c)
{
    dctx->window[dctx->winpos] = c;
    dctx->winpos = (dctx->winpos + 1) & (WINSIZE - 1);
    if (dctx->outlen >= dctx->outsize) {
        dctx->outsize = dctx->outlen + 512;
        dctx->outblk = sresize(dctx->outblk, dctx->outsize, unsigned char);
    }
    if (dctx->type == DEFLATE_TYPE_ZLIB) {
        unsigned char uc = c;
        dctx->adler32 = adler32_update(dctx->adler32, &uc, 1);
    }
    dctx->outblk[dctx->outlen++] = c;
}

#define EATBITS(n) ( dctx->nbits -= (n), dctx->bits >>= (n) )

int deflate_decompress_data(deflate_decompress_ctx *dctx,
                            const void *vblock, int len,
                            void **outblock, int *outlen)
{
    const coderecord *rec;
    const unsigned char *block = (const unsigned char *)vblock;
    int code, bfinal, btype, rep, dist, nlen, header, adler;

    dctx->outblk = snewn(256, unsigned char);
    dctx->outsize = 256;
    dctx->outlen = 0;

    while (len > 0 || dctx->nbits > 0) {
        while (dctx->nbits < 24 && len > 0) {
            dctx->bits |= (*block++) << dctx->nbits;
            dctx->nbits += 8;
            len--;
        }
        switch (dctx->state) {
          case START:
            /* Expect 16-bit zlib header. */
            if (dctx->nbits < 16)
                goto finished;         /* done all we can */

            /*
             * The header is stored as a big-endian 16-bit integer,
             * in contrast to the general little-endian policy in
             * the rest of the format :-(
             */
            header = (((dctx->bits & 0xFF00) >> 8) |
                      ((dctx->bits & 0x00FF) << 8));
            EATBITS(16);

            /*
             * Check the header:
             *
             *  - bits 8-11 should be 1000 (Deflate/RFC1951)
             *  - bits 12-15 should be at most 0111 (window size)
             *  - bit 5 should be zero (no dictionary present)
             *  - we don't care about bits 6-7 (compression rate)
             *  - bits 0-4 should be set up to make the whole thing
             *    a multiple of 31 (checksum).
             */
            if ((header & 0x0F00) != 0x0800 ||
                (header & 0xF000) >  0x7000 ||
                (header & 0x0020) != 0x0000 ||
                (header % 31) != 0)
                goto decode_error;

            dctx->state = OUTSIDEBLK;
            break;
          case OUTSIDEBLK:
            /* Expect 3-bit block header. */
            if (dctx->nbits < 3)
                goto finished;         /* done all we can */
            bfinal = dctx->bits & 1;
            if (bfinal)
                dctx->lastblock = TRUE;
            EATBITS(1);
            btype = dctx->bits & 3;
            EATBITS(2);
            if (btype == 0) {
                int to_eat = dctx->nbits & 7;
                dctx->state = UNCOMP_LEN;
                EATBITS(to_eat);       /* align to byte boundary */
            } else if (btype == 1) {
                dctx->currlentable = dctx->staticlentable;
                dctx->currdisttable = dctx->staticdisttable;
                dctx->state = INBLK;
            } else if (btype == 2) {
                dctx->state = TREES_HDR;
            }
            debug(("recv: bfinal=%d btype=%d\n", bfinal, btype));
            break;
          case TREES_HDR:
            /*
             * Dynamic block header. Five bits of HLIT, five of
             * HDIST, four of HCLEN.
             */
            if (dctx->nbits < 5 + 5 + 4)
                goto finished;         /* done all we can */
            dctx->hlit = 257 + (dctx->bits & 31);
            EATBITS(5);
            dctx->hdist = 1 + (dctx->bits & 31);
            EATBITS(5);
            dctx->hclen = 4 + (dctx->bits & 15);
            EATBITS(4);
            debug(("recv: hlit=%d hdist=%d hclen=%d\n", dctx->hlit,
                   dctx->hdist, dctx->hclen));
            dctx->lenptr = 0;
            dctx->state = TREES_LENLEN;
            memset(dctx->lenlen, 0, sizeof(dctx->lenlen));
            break;
          case TREES_LENLEN:
            if (dctx->nbits < 3)
                goto finished;
            while (dctx->lenptr < dctx->hclen && dctx->nbits >= 3) {
                dctx->lenlen[lenlenmap[dctx->lenptr++]] =
                    (unsigned char) (dctx->bits & 7);
                debug(("recv: lenlen %d\n", (unsigned char) (dctx->bits & 7)));
                EATBITS(3);
            }
            if (dctx->lenptr == dctx->hclen) {
                dctx->lenlentable = mktable(dctx->lenlen, 19);
                dctx->state = TREES_LEN;
                dctx->lenptr = 0;
            }
            break;
          case TREES_LEN:
            if (dctx->lenptr >= dctx->hlit + dctx->hdist) {
                dctx->currlentable = mktable(dctx->lengths, dctx->hlit);
                dctx->currdisttable = mktable(dctx->lengths + dctx->hlit,
                                              dctx->hdist);
                freetable(&dctx->lenlentable);
                dctx->lenlentable = NULL;
                dctx->state = INBLK;
                break;
            }
            code = huflookup(&dctx->bits, &dctx->nbits, dctx->lenlentable);
            debug(("recv: codelen %d\n", code));
            if (code == -1)
                goto finished;
            if (code == -2)
                goto decode_error;
            if (code < 16)
                dctx->lengths[dctx->lenptr++] = code;
            else {
                dctx->lenextrabits = (code == 16 ? 2 : code == 17 ? 3 : 7);
                dctx->lenaddon = (code == 18 ? 11 : 3);
                dctx->lenrep = (code == 16 && dctx->lenptr > 0 ?
                                dctx->lengths[dctx->lenptr - 1] : 0);
                dctx->state = TREES_LENREP;
            }
            break;
          case TREES_LENREP:
            if (dctx->nbits < dctx->lenextrabits)
                goto finished;
            rep =
                dctx->lenaddon +
                (dctx->bits & ((1 << dctx->lenextrabits) - 1));
            EATBITS(dctx->lenextrabits);
            if (dctx->lenextrabits)
                debug(("recv: codelen-extrabits %d/%d\n", rep - dctx->lenaddon,
                       dctx->lenextrabits));
            while (rep > 0 && dctx->lenptr < dctx->hlit + dctx->hdist) {
                dctx->lengths[dctx->lenptr] = dctx->lenrep;
                dctx->lenptr++;
                rep--;
            }
            dctx->state = TREES_LEN;
            break;
          case INBLK:
            code = huflookup(&dctx->bits, &dctx->nbits, dctx->currlentable);
            debug(("recv: litlen %d\n", code));
            if (code == -1)
                goto finished;
            if (code == -2)
                goto decode_error;
            if (code < 256)
                emit_char(dctx, code);
            else if (code == 256) {
                if (dctx->lastblock)
                    dctx->state = END;
                else
                    dctx->state = OUTSIDEBLK;
                if (dctx->currlentable != dctx->staticlentable) {
                    freetable(&dctx->currlentable);
                    dctx->currlentable = NULL;
                }
                if (dctx->currdisttable != dctx->staticdisttable) {
                    freetable(&dctx->currdisttable);
                    dctx->currdisttable = NULL;
                }
            } else if (code < 286) {   /* static tree can give >285; ignore */
                dctx->state = GOTLENSYM;
                dctx->sym = code;
            }
            break;
          case GOTLENSYM:
            rec = &lencodes[dctx->sym - 257];
            if (dctx->nbits < rec->extrabits)
                goto finished;
            dctx->len =
                rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
            if (rec->extrabits)
                debug(("recv: litlen-extrabits %d/%d\n",
                       dctx->len - rec->min, rec->extrabits));
            EATBITS(rec->extrabits);
            dctx->state = GOTLEN;
            break;
          case GOTLEN:
            code = huflookup(&dctx->bits, &dctx->nbits, dctx->currdisttable);
            debug(("recv: dist %d\n", code));
            if (code == -1)
                goto finished;
            if (code == -2)
                goto decode_error;
            dctx->state = GOTDISTSYM;
            dctx->sym = code;
            break;
          case GOTDISTSYM:
            rec = &distcodes[dctx->sym];
            if (dctx->nbits < rec->extrabits)
                goto finished;
            dist = rec->min + (dctx->bits & ((1 << rec->extrabits) - 1));
            if (rec->extrabits)
                debug(("recv: dist-extrabits %d/%d\n",
                       dist - rec->min, rec->extrabits));
            EATBITS(rec->extrabits);
            dctx->state = INBLK;
            while (dctx->len--)
                emit_char(dctx, dctx->window[(dctx->winpos - dist) &
                                             (WINSIZE - 1)]);
            break;
          case UNCOMP_LEN:
            /*
             * Uncompressed block. We expect to see a 16-bit LEN.
             */
            if (dctx->nbits < 16)
                goto finished;
            dctx->uncomplen = dctx->bits & 0xFFFF;
            EATBITS(16);
            dctx->state = UNCOMP_NLEN;
            break;
          case UNCOMP_NLEN:
            /*
             * Uncompressed block. We expect to see a 16-bit NLEN,
             * which should be the one's complement of the previous
             * LEN.
             */
            if (dctx->nbits < 16)
                goto finished;
            nlen = dctx->bits & 0xFFFF;
            EATBITS(16);
            if (dctx->uncomplen == 0)
                dctx->state = OUTSIDEBLK;       /* block is empty */
            else
                dctx->state = UNCOMP_DATA;
            break;
          case UNCOMP_DATA:
            if (dctx->nbits < 8)
                goto finished;
            emit_char(dctx, dctx->bits & 0xFF);
            EATBITS(8);
            if (--dctx->uncomplen == 0)
                dctx->state = OUTSIDEBLK;       /* end of uncompressed block */
            break;
          case END:
            /*
             * End of compressed data. We align to a byte boundary,
             * and then look for format-specific trailer data.
             */
            {
                int to_eat = dctx->nbits & 7;
                EATBITS(to_eat);
            }
            if (dctx->type == DEFLATE_TYPE_ZLIB)
                dctx->state = ADLER1;
            else
                dctx->state = FINALSPIN;
            break;
          case ADLER1:
            if (dctx->nbits < 16)
                goto finished;
            adler = (dctx->bits & 0xFF) << 8;
            EATBITS(8);
            adler |= (dctx->bits & 0xFF);
            EATBITS(8);
            if (adler != ((dctx->adler32 >> 16) & 0xFFFF))
                goto decode_error;
            dctx->state = ADLER2;
            break;
          case ADLER2:
            if (dctx->nbits < 16)
                goto finished;
            adler = (dctx->bits & 0xFF) << 8;
            EATBITS(8);
            adler |= (dctx->bits & 0xFF);
            EATBITS(8);
            if (adler != (dctx->adler32 & 0xFFFF))
                goto decode_error;
            dctx->state = FINALSPIN;
            break;
          case FINALSPIN:
            /* Just ignore any trailing garbage on the data stream. */
            EATBITS(dctx->nbits);
            break;
        }
    }

    finished:
    *outblock = dctx->outblk;
    *outlen = dctx->outlen;
    return 1;

    decode_error:
    sfree(dctx->outblk);
    *outblock = dctx->outblk = NULL;
    *outlen = 0;
    return 0;
}

#ifdef STANDALONE

int main(int argc, char **argv)
{
    unsigned char buf[65536], *outbuf;
    int ret, outlen;
    deflate_decompress_ctx *dhandle;
    deflate_compress_ctx *chandle;
    int type = DEFLATE_TYPE_ZLIB, opts = TRUE, compress = FALSE;
    char *filename = NULL;
    FILE *fp;

    while (--argc) {
        char *p = *++argv;

        if (p[0] == '-' && opts) {
            if (!strcmp(p, "-d"))
                type = DEFLATE_TYPE_BARE;
            if (!strcmp(p, "-c"))
                compress = TRUE;
            else if (!strcmp(p, "--"))
                opts = FALSE;          /* next thing is filename */
            else {
                fprintf(stderr, "unknown command line option '%s'\n", p);
                return 1;
            }
        } else if (!filename) {
            filename = p;
        } else {
            fprintf(stderr, "can only handle one filename\n");
            return 1;
        }
    }

    if (compress) {
        chandle = deflate_compress_new(type);
        dhandle = NULL;
    } else {
        dhandle = deflate_decompress_new(type);
        chandle = NULL;
    }

    if (filename)
        fp = fopen(filename, "rb");
    else
        fp = stdin;

    if (!fp) {
        assert(filename);
        fprintf(stderr, "unable to open '%s'\n", filename);
        return 1;
    }

    do {
        ret = fread(buf, 1, sizeof(buf), fp);
        if (dhandle) {
            if (ret > 0)
                deflate_decompress_data(dhandle, buf, ret,
                                        (void **)&outbuf, &outlen);
        } else {
            if (ret > 0)
                deflate_compress_data(chandle, buf, ret, DEFLATE_NO_FLUSH,
                                      (void **)&outbuf, &outlen);
            else
                deflate_compress_data(chandle, buf, ret, DEFLATE_END_OF_DATA,
                                      (void **)&outbuf, &outlen);
        }
        if (outbuf) {
            if (outlen)
                fwrite(outbuf, 1, outlen, stdout);
            sfree(outbuf);
        } else if (dhandle) {
            fprintf(stderr, "decoding error\n");
            return 1;
        }
    } while (ret > 0);

    if (dhandle)
        deflate_decompress_free(dhandle);
    if (chandle)
        deflate_compress_free(chandle);

    if (filename)
        fclose(fp);

    return 0;
}

#endif

#ifdef TESTMODE

int main(int argc, char **argv)
{
    char *filename = NULL;
    FILE *fp;
    deflate_compress_ctx *chandle;
    deflate_decompress_ctx *dhandle;
    unsigned char buf[65536], *outbuf, *outbuf2;
    int ret, outlen, outlen2;
    int dlen = 0, clen = 0;
    int opts = TRUE;

    while (--argc) {
        char *p = *++argv;

        if (p[0] == '-' && opts) {
            if (!strcmp(p, "--"))
                opts = FALSE;          /* next thing is filename */
            else {
                fprintf(stderr, "unknown command line option '%s'\n", p);
                return 1;
            }
        } else if (!filename) {
            filename = p;
        } else {
            fprintf(stderr, "can only handle one filename\n");
            return 1;
        }
    }

    if (filename)
        fp = fopen(filename, "rb");
    else
        fp = stdin;

    if (!fp) {
        assert(filename);
        fprintf(stderr, "unable to open '%s'\n", filename);
        return 1;
    }

    chandle = deflate_compress_new(DEFLATE_TYPE_ZLIB);
    dhandle = deflate_decompress_new(DEFLATE_TYPE_ZLIB);

    do {
        ret = fread(buf, 1, sizeof(buf), fp);
        if (ret <= 0) {
            deflate_compress_data(chandle, NULL, 0, DEFLATE_END_OF_DATA,
                                  (void **)&outbuf, &outlen);
        } else {
            dlen += ret;
            deflate_compress_data(chandle, buf, ret, DEFLATE_NO_FLUSH,
                                  (void **)&outbuf, &outlen);
        }
        if (outbuf) {
            clen += outlen;
            deflate_decompress_data(dhandle, outbuf, outlen,
                                    (void **)&outbuf2, &outlen2);
            sfree(outbuf);
            if (outbuf2) {
                if (outlen2)
                    fwrite(outbuf2, 1, outlen2, stdout);
                sfree(outbuf2);
            } else {
                fprintf(stderr, "decoding error\n");
                return 1;
            }
        }
    } while (ret > 0);

    fprintf(stderr, "%d plaintext -> %d compressed\n", dlen, clen);

    return 0;
}

#endif