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# exponentd.m4 serial 3
dnl Copyright (C) 2007-2008, 2010-2021 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([gl_DOUBLE_EXPONENT_LOCATION],
[
AC_CACHE_CHECK([where to find the exponent in a 'double'],
[gl_cv_cc_double_expbit0],
[
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[
#include <float.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#define NWORDS \
((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
typedef union { double value; unsigned int word[NWORDS]; } memory_double;
static unsigned int ored_words[NWORDS];
static unsigned int anded_words[NWORDS];
static void add_to_ored_words (double x)
{
memory_double m;
size_t i;
/* Clear it first, in case sizeof (double) < sizeof (memory_double). */
memset (&m, 0, sizeof (memory_double));
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 (0.25);
add_to_ored_words (0.5);
add_to_ored_words (1.0);
add_to_ored_words (2.0);
add_to_ored_words (4.0);
/* 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_double_expbit0=`cat conftest.out`],
[gl_cv_cc_double_expbit0="unknown"],
[
dnl On ARM, there are two 'double' floating-point formats, used by
dnl different sets of instructions: The older FPA instructions assume
dnl that they are stored in big-endian word order, while the words
dnl (like integer types) are stored in little-endian byte order.
dnl The newer VFP instructions assume little-endian order
dnl consistently.
AC_EGREP_CPP([mixed_endianness], [
#if defined arm || defined __arm || defined __arm__
mixed_endianness
#endif
],
[gl_cv_cc_double_expbit0="unknown"],
[
pushdef([AC_MSG_CHECKING],[:])dnl
pushdef([AC_MSG_RESULT],[:])dnl
pushdef([AC_MSG_RESULT_UNQUOTED],[:])dnl
AC_C_BIGENDIAN(
[gl_cv_cc_double_expbit0="word 0 bit 20"],
[gl_cv_cc_double_expbit0="word 1 bit 20"],
[gl_cv_cc_double_expbit0="unknown"])
popdef([AC_MSG_RESULT_UNQUOTED])dnl
popdef([AC_MSG_RESULT])dnl
popdef([AC_MSG_CHECKING])dnl
])
])
rm -f conftest.out
])
case "$gl_cv_cc_double_expbit0" in
word*bit*)
word=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
bit=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word.*bit //'`
AC_DEFINE_UNQUOTED([DBL_EXPBIT0_WORD], [$word],
[Define as the word index where to find the exponent of 'double'.])
AC_DEFINE_UNQUOTED([DBL_EXPBIT0_BIT], [$bit],
[Define as the bit index in the word where to find bit 0 of the exponent of 'double'.])
;;
esac
])
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