gnulib/import/m4/exponentl.m4

   1 # exponentl.m4 serial 3
   2 dnl Copyright (C) 2007-2016 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_CACHE_CHECK([where to find the exponent in a 'long double'],
  10     [gl_cv_cc_long_double_expbit0],
  11     [
  12       AC_RUN_IFELSE(
  13         [AC_LANG_SOURCE([[
  14 #include <float.h>
  15 #include <stddef.h>
  16 #include <stdio.h>
  17 #include <string.h>
  18 #define NWORDS \
  19   ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
  20 typedef union { long double value; unsigned int word[NWORDS]; }
  21         memory_long_double;
  22 static unsigned int ored_words[NWORDS];
  23 static unsigned int anded_words[NWORDS];
  24 static void add_to_ored_words (long double x)
  25 {
  26   memory_long_double m;
  27   size_t i;
  28   /* Clear it first, in case
  29      sizeof (long double) < sizeof (memory_long_double).  */
  30   memset (&m, 0, sizeof (memory_long_double));
  31   m.value = x;
  32   for (i = 0; i < NWORDS; i++)
  33     {
  34       ored_words[i] |= m.word[i];
  35       anded_words[i] &= m.word[i];
  36     }
  37 }
  38 int main ()
  39 {
  40   size_t j;
  41   FILE *fp = fopen ("conftest.out", "w");
  42   if (fp == NULL)
  43     return 1;
  44   for (j = 0; j < NWORDS; j++)
  45     anded_words[j] = ~ (unsigned int) 0;
  46   add_to_ored_words (0.25L);
  47   add_to_ored_words (0.5L);
  48   add_to_ored_words (1.0L);
  49   add_to_ored_words (2.0L);
  50   add_to_ored_words (4.0L);
  51   /* Remove bits that are common (e.g. if representation of the first mantissa
  52      bit is explicit).  */
  53   for (j = 0; j < NWORDS; j++)
  54     ored_words[j] &= ~anded_words[j];
  55   /* Now find the nonzero word.  */
  56   for (j = 0; j < NWORDS; j++)
  57     if (ored_words[j] != 0)
  58       break;
  59   if (j < NWORDS)
  60     {
  61       size_t i;
  62       for (i = j + 1; i < NWORDS; i++)
  63         if (ored_words[i] != 0)
  64           {
  65             fprintf (fp, "unknown");
  66             return (fclose (fp) != 0);
  67           }
  68       for (i = 0; ; i++)
  69         if ((ored_words[j] >> i) & 1)
  70           {
  71             fprintf (fp, "word %d bit %d", (int) j, (int) i);
  72             return (fclose (fp) != 0);
  73           }
  74     }
  75   fprintf (fp, "unknown");
  76   return (fclose (fp) != 0);
  77 }
  78         ]])],
  79         [gl_cv_cc_long_double_expbit0=`cat conftest.out`],
  80         [gl_cv_cc_long_double_expbit0="unknown"],
  81         [
  82           dnl When cross-compiling, we don't know. It depends on the
  83           dnl ABI and compiler version. There are too many cases.
  84           gl_cv_cc_long_double_expbit0="unknown"
  85         ])
  86       rm -f conftest.out
  87     ])
  88   case "$gl_cv_cc_long_double_expbit0" in
  89     word*bit*)
  90       word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
  91       bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'`
  92       AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word],
  93         [Define as the word index where to find the exponent of 'long double'.])
  94       AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit],
  95         [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.])
  96       ;;
  97   esac
  98 ])