-
-AC_DEFUN([gl_FLOAT_EXPONENT_LOCATION],
-[
- AC_CACHE_CHECK([where to find the exponent in a 'float'],
- [gl_cv_cc_float_expbit0],
- [
- AC_TRY_RUN([
-#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_double_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
-])