git.distorted.org.uk Git - u/mdw/catacomb/blob - mptypes.c

   1 /* -*-c-*-
   2  *
   3  * Program to find appropriate types for multiprecision integer stuff.
   4  */
   5
   6 #define _GNU_SOURCE
   7 #include <stdio.h>
   8 #include <limits.h>
   9 #if __STDC_VERSION__ >= 199900l
  10 #  include <stdint.h>
  11 #endif
  12
  13 /* --- Hack for GCC --- *
  14  *
  15  * WG14 in their infinite wisdom decided not to use the GCC constant name.
  16  */
  17
  18 #if defined(ULONG_LONG_MAX) && !defined(ULLONG_MAX)
  19 #  define ULLONG_MAX ULONG_LONG_MAX
  20 #endif
  21
  22 /* --- Choose the largest integer type --- */
  23
  24 #if defined(UINTMAX_MAX)
  25   typedef uintmax_t umax;
  26 # define P_UMAX PRIuMAX
  27 #elif defined(ULLONG_MAX)
  28   typedef unsigned long long umax;
  29 # define P_UMAX "%llu"
  30 #else
  31   typedef unsigned long umax;
  32 # define P_UMAX "%lu"
  33 #endif
  34
  35 /* --- Table of interesting types --- *
  36  *
  37  * These are in preference order.
  38  */
  39
  40 enum {
  41   f_stdint
  42 };
  43
  44 struct itype {
  45   const char *name;
  46   umax max;
  47   unsigned flags;
  48   unsigned bits;
  49 } tytab[] = {
  50   { "unsigned int",             UINT_MAX,       0 },
  51   { "unsigned short",           USHRT_MAX,      0 },
  52   { "unsigned long",            ULONG_MAX,      0 },
  53 #ifdef ULLONG_MAX
  54   { "unsigned long long",       ULLONG_MAX,     0 },
  55 #endif
  56 #ifdef UINTMAX_MAX
  57   { "uintmax_t",                UINTMAX_MAX,    f_stdint },
  58 #endif
  59   { 0,                          0 },
  60 };
  61
  62 typedef struct itype itype;
  63
  64 /* --- Main program --- */
  65
  66 int main(int argc, char *argv[])
  67 {
  68   itype *i;
  69   itype *largest, *mpw, *mpd;
  70
  71   /* --- Find the bitcounts --- */
  72
  73   for (i = tytab; i->name; i++) {
  74     unsigned bits;
  75     umax u = i->max;
  76     for (bits = 0; u; bits++)
  77       u >>= 1;
  78     i->bits = bits;
  79   }
  80
  81   /* --- Now try to find the interesting types --- *
  82    *
  83    * The first thing to do is to find the largest type.  Then I find the
  84    * `best' type which is less than half that size, and then the `best' type
  85    * which is twice as big as that one.
  86    */
  87
  88   largest = tytab;
  89   for (i = tytab; i->name; i++) {
  90     if (i->bits > largest->bits)
  91       largest = i;
  92   }
  93   for (mpw = 0, i = tytab; i->name; i++) {
  94     if (i->bits * 2 <= largest->bits && (!mpw || i->bits > mpw->bits))
  95       mpw = i;
  96   }
  97   if (!mpw)
  98     mpw = tytab;
  99   for (mpd = 0, i = tytab; i->name; i++) {
 100     if (i->bits >= mpw->bits * 2 && (!mpd || i->bits < mpd->bits))
 101       mpd = i;
 102   }
 103   if (!mpd) {
 104     static itype w, d;
 105     d = w = *mpw;
 106     w.bits /= 2; w.max = ~(~((umax)0) << w.bits);
 107     d.bits = w.bits * 2; d.max = ~(~((umax)0) << d.bits);
 108     mpw = &w; mpd = &d;
 109   }
 110
 111   /* --- Output time --- */
 112
 113   puts("\
 114 /* -*-c-*-\n\
 115  *\n\
 116  * mptypes.h [generated]\n\
 117  */\n\
 118 \n\
 119 #ifndef MPTYPES_H\n\
 120 #define MPTYPES_H\n\
 121 ");
 122   if ((mpd->flags | mpw->flags) & f_stdint) {
 123     puts("\
 124 #if __STDC_VERSION__ >= 199900l\n\
 125 #  include <stdint.h>\n\
 126 #endif\n\
 127 ");
 128   }
 129   printf("\
 130 typedef %s mpw;\n\
 131 #define MPW_BITS %u\n\
 132 #define MPW_MAX " P_UMAX "\n\
 133 \n\
 134 typedef %s mpd;\n\
 135 #define MPD_BITS %u\n\
 136 #define MPD_MAX " P_UMAX "\n\
 137 \n\
 138 #endif\n\
 139 ",
 140   mpw->name, mpw->bits, mpw->max,
 141   mpd->name, mpd->bits, mpd->max);
 142
 143   return (0);
 144 }