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# exponentf.m4 serial 3
dnl Copyright (C) 2007-2008, 2010-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
AC_DEFUN_ONCE([gl_FLOAT_EXPONENT_LOCATION],
[
AC_CACHE_CHECK([where to find the exponent in a 'float'],
[gl_cv_cc_float_expbit0],
[
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[
#include <float.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#define NWORDS \
((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
typedef union { float value; unsigned int word[NWORDS]; } memory_float;
static unsigned int ored_words[NWORDS];
static unsigned int anded_words[NWORDS];
static void add_to_ored_words (float x)
{
memory_float m;
size_t i;
/* Clear it first, in case
sizeof (float) < sizeof (memory_float). */
memset (&m, 0, sizeof (memory_float));
m.value = x;
for (i = 0; i < NWORDS; i++)
{
ored_words[i] |= m.word[i];
anded_words[i] &= m.word[i];
}
}
int main ()
{
size_t j;
FILE *fp = fopen ("conftest.out", "w");
if (fp == NULL)
return 1;
for (j = 0; j < NWORDS; j++)
anded_words[j] = ~ (unsigned int) 0;
add_to_ored_words (0.25f);
add_to_ored_words (0.5f);
add_to_ored_words (1.0f);
add_to_ored_words (2.0f);
add_to_ored_words (4.0f);
/* Remove bits that are common (e.g. if representation of the first mantissa
bit is explicit). */
for (j = 0; j < NWORDS; j++)
ored_words[j] &= ~anded_words[j];
/* Now find the nonzero word. */
for (j = 0; j < NWORDS; j++)
if (ored_words[j] != 0)
break;
if (j < NWORDS)
{
size_t i;
for (i = j + 1; i < NWORDS; i++)
if (ored_words[i] != 0)
{
fprintf (fp, "unknown");
return (fclose (fp) != 0);
}
for (i = 0; ; i++)
if ((ored_words[j] >> i) & 1)
{
fprintf (fp, "word %d bit %d", (int) j, (int) i);
return (fclose (fp) != 0);
}
}
fprintf (fp, "unknown");
return (fclose (fp) != 0);
}
]])],
[gl_cv_cc_float_expbit0=`cat conftest.out`],
[gl_cv_cc_float_expbit0="unknown"],
[gl_cv_cc_float_expbit0="word 0 bit 23"])
rm -f conftest.out
])
case "$gl_cv_cc_float_expbit0" in
word*bit*)
word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'`
AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word],
[Define as the word index where to find the exponent of 'float'.])
AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit],
[Define as the bit index in the word where to find bit 0 of the exponent of 'float'.])
;;
esac
])
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