gnulib/import/m4/exponentl.m4

   1 # exponentl.m4 serial 4
   2 dnl Copyright (C) 2007-2019 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6 AC_DEFUN([gl_LONG_DOUBLE_EXPONENT_LOCATION],
   7 [
   8   AC_REQUIRE([gl_BIGENDIAN])
   9   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
  10   AC_CACHE_CHECK([where to find the exponent in a 'long double'],
  11     [gl_cv_cc_long_double_expbit0],
  12     [
  13       AC_RUN_IFELSE(
  14         [AC_LANG_SOURCE([[
  15 #include <float.h>
  16 #include <stddef.h>
  17 #include <stdio.h>
  18 #include <string.h>
  19 #define NWORDS \
  20   ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
  21 typedef union { long double value; unsigned int word[NWORDS]; }
  22         memory_long_double;
  23 static unsigned int ored_words[NWORDS];
  24 static unsigned int anded_words[NWORDS];
  25 static void add_to_ored_words (long double x)
  26 {
  27   memory_long_double m;
  28   size_t i;
  29   /* Clear it first, in case
  30      sizeof (long double) < sizeof (memory_long_double).  */
  31   memset (&m, 0, sizeof (memory_long_double));
  32   m.value = x;
  33   for (i = 0; i < NWORDS; i++)
  34     {
  35       ored_words[i] |= m.word[i];
  36       anded_words[i] &= m.word[i];
  37     }
  38 }
  39 int main ()
  40 {
  41   size_t j;
  42   FILE *fp = fopen ("conftest.out", "w");
  43   if (fp == NULL)
  44     return 1;
  45   for (j = 0; j < NWORDS; j++)
  46     anded_words[j] = ~ (unsigned int) 0;
  47   add_to_ored_words (0.25L);
  48   add_to_ored_words (0.5L);
  49   add_to_ored_words (1.0L);
  50   add_to_ored_words (2.0L);
  51   add_to_ored_words (4.0L);
  52   /* Remove bits that are common (e.g. if representation of the first mantissa
  53      bit is explicit).  */
  54   for (j = 0; j < NWORDS; j++)
  55     ored_words[j] &= ~anded_words[j];
  56   /* Now find the nonzero word.  */
  57   for (j = 0; j < NWORDS; j++)
  58     if (ored_words[j] != 0)
  59       break;
  60   if (j < NWORDS)
  61     {
  62       size_t i;
  63       for (i = j + 1; i < NWORDS; i++)
  64         if (ored_words[i] != 0)
  65           {
  66             fprintf (fp, "unknown");
  67             return (fclose (fp) != 0);
  68           }
  69       for (i = 0; ; i++)
  70         if ((ored_words[j] >> i) & 1)
  71           {
  72             fprintf (fp, "word %d bit %d", (int) j, (int) i);
  73             return (fclose (fp) != 0);
  74           }
  75     }
  76   fprintf (fp, "unknown");
  77   return (fclose (fp) != 0);
  78 }
  79         ]])],
  80         [gl_cv_cc_long_double_expbit0=`cat conftest.out`],
  81         [gl_cv_cc_long_double_expbit0="unknown"],
  82         [
  83           dnl When cross-compiling, in general we don't know. It depends on the
  84           dnl ABI and compiler version. There are too many cases.
  85           gl_cv_cc_long_double_expbit0="unknown"
  86           case "$host_os" in
  87             mingw*) # On native Windows (little-endian), we know the result
  88                     # in two cases: mingw, MSVC.
  89               AC_EGREP_CPP([Known], [
  90 #ifdef __MINGW32__
  91  Known
  92 #endif
  93                 ], [gl_cv_cc_long_double_expbit0="word 2 bit 0"])
  94               AC_EGREP_CPP([Known], [
  95 #ifdef _MSC_VER
  96  Known
  97 #endif
  98                 ], [gl_cv_cc_long_double_expbit0="word 1 bit 20"])
  99               ;;
 100           esac
 101         ])
 102       rm -f conftest.out
 103     ])
 104   case "$gl_cv_cc_long_double_expbit0" in
 105     word*bit*)
 106       word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
 107       bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'`
 108       AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word],
 109         [Define as the word index where to find the exponent of 'long double'.])
 110       AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit],
 111         [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.])
 112       ;;
 113   esac
 114 ])