Build `mptypes.h' header file appropriately for the current

[u/mdw/catacomb] / mptypes.c

/* -*-c-*-
 *
 * Program to find appropriate types for multiprecision integer stuff.
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <limits.h>
#if __STDC_VERSION__ >= 199900l
#  include <stdint.h>
#endif

/* --- Hack for GCC --- *
 *
 * WG14 in their infinite wisdom decided not to use the GCC constant name.
 */

#if defined(ULONG_LONG_MAX) && !defined(ULLONG_MAX)
#  define ULLONG_MAX ULONG_LONG_MAX
#endif

/* --- Choose the largest integer type --- */

#if defined(UINTMAX_MAX)
  typedef uintmax_t umax;
# define P_UMAX PRIuMAX
#elif defined(ULLONG_MAX)
  typedef unsigned long long umax;
# define P_UMAX "%llu"
#else
  typedef unsigned long umax;
# define P_UMAX "%lu"
#endif

/* --- Table of interesting types --- *
 *
 * These are in preference order.
 */

enum {
  f_stdint
};

struct itype {
  const char *name;
  umax max;
  unsigned flags;
  unsigned bits;
} tytab[] = {
  { "unsigned int",		UINT_MAX,	0 },
  { "unsigned short",		USHRT_MAX,	0 },
  { "unsigned long",		ULONG_MAX,	0 },
#ifdef ULLONG_MAX
  { "unsigned long long",	ULLONG_MAX,	0 },
#endif
#ifdef UINTMAX_MAX
  { "uintmax_t",		UINTMAX_MAX,	f_stdint },
#endif
  { 0,				0 },
};

typedef struct itype itype;

/* --- Main program --- */

int main(int argc, char *argv[])
{
  itype *i;
  itype *largest, *mpw, *mpd;

  /* --- Find the bitcounts --- */

  for (i = tytab; i->name; i++) {
    unsigned bits;
    umax u = i->max;
    for (bits = 0; u; bits++)
      u >>= 1;
    i->bits = bits;
  }

  /* --- Now try to find the interesting types --- *
   *
   * The first thing to do is to find the largest type.  Then I find the
   * `best' type which is less than half that size, and then the `best' type
   * which is twice as big as that one.
   */

  largest = tytab;
  for (i = tytab; i->name; i++) {
    if (i->bits > largest->bits)
      largest = i;
  }
  for (mpw = 0, i = tytab; i->name; i++) {
    if (i->bits * 2 <= largest->bits && (!mpw || i->bits > mpw->bits))
      mpw = i;
  }
  if (!mpw)
    mpw = tytab;
  for (mpd = 0, i = tytab; i->name; i++) {
    if (i->bits >= mpw->bits * 2 && (!mpd || i->bits < mpd->bits))
      mpd = i;
  }
  if (!mpd) {
    static itype w, d;
    d = w = *mpw;
    w.bits /= 2; w.max = ~(~((umax)0) << w.bits);
    d.bits = w.bits * 2; d.max = ~(~((umax)0) << d.bits);
    mpw = &w; mpd = &d;
  }    

  /* --- Output time --- */

  puts("\
/* -*-c-*-\n\
 *\n\
 * mptypes.h [generated]\n\
 */\n\
\n\
#ifndef MPTYPES_H\n\
#define MPTYPES_H\n\
");
  if ((mpd->flags | mpw->flags) & f_stdint) {
    puts("\
#if __STDC_VERSION__ >= 199900l\n\
#  include <stdint.h>\n\
#endif\n\
");
  }
  printf("\
typedef %s mpw;\n\
#define MPW_BITS %u\n\
#define MPW_MAX " P_UMAX "\n\
\n\
typedef %s mpd;\n\
#define MPD_BITS %u\n\
#define MPD_MAX " P_UMAX "\n\
\n\
#endif\n\
",
  mpw->name, mpw->bits, mpw->max,
  mpd->name, mpd->bits, mpd->max);

  return (0);
}