93 lines
2.8 KiB
Plaintext
93 lines
2.8 KiB
Plaintext
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# exponentf.m4 serial 2
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dnl Copyright (C) 2007-2008, 2010-2023 Free Software Foundation, Inc.
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dnl This file is free software; the Free Software Foundation
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dnl gives unlimited permission to copy and/or distribute it,
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dnl with or without modifications, as long as this notice is preserved.
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AC_DEFUN([gl_FLOAT_EXPONENT_LOCATION],
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[
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AC_CACHE_CHECK([where to find the exponent in a 'float'],
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[gl_cv_cc_float_expbit0],
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[
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AC_RUN_IFELSE(
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[AC_LANG_SOURCE([[
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#include <float.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <string.h>
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#define NWORDS \
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((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
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typedef union { float value; unsigned int word[NWORDS]; } memory_float;
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static unsigned int ored_words[NWORDS];
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static unsigned int anded_words[NWORDS];
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static void add_to_ored_words (float x)
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{
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memory_float m;
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size_t i;
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/* Clear it first, in case
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sizeof (float) < sizeof (memory_float). */
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memset (&m, 0, sizeof (memory_float));
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m.value = x;
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for (i = 0; i < NWORDS; i++)
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{
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ored_words[i] |= m.word[i];
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anded_words[i] &= m.word[i];
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}
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}
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int main ()
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{
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size_t j;
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FILE *fp = fopen ("conftest.out", "w");
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if (fp == NULL)
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return 1;
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for (j = 0; j < NWORDS; j++)
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anded_words[j] = ~ (unsigned int) 0;
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add_to_ored_words (0.25f);
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add_to_ored_words (0.5f);
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add_to_ored_words (1.0f);
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add_to_ored_words (2.0f);
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add_to_ored_words (4.0f);
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/* Remove bits that are common (e.g. if representation of the first mantissa
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bit is explicit). */
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for (j = 0; j < NWORDS; j++)
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ored_words[j] &= ~anded_words[j];
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/* Now find the nonzero word. */
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for (j = 0; j < NWORDS; j++)
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if (ored_words[j] != 0)
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break;
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if (j < NWORDS)
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{
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size_t i;
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for (i = j + 1; i < NWORDS; i++)
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if (ored_words[i] != 0)
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{
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fprintf (fp, "unknown");
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return (fclose (fp) != 0);
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}
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for (i = 0; ; i++)
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if ((ored_words[j] >> i) & 1)
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{
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fprintf (fp, "word %d bit %d", (int) j, (int) i);
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return (fclose (fp) != 0);
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}
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}
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fprintf (fp, "unknown");
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return (fclose (fp) != 0);
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}
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]])],
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[gl_cv_cc_float_expbit0=`cat conftest.out`],
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[gl_cv_cc_float_expbit0="unknown"],
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[gl_cv_cc_float_expbit0="word 0 bit 23"])
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rm -f conftest.out
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])
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case "$gl_cv_cc_float_expbit0" in
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word*bit*)
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word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
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bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'`
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AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word],
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[Define as the word index where to find the exponent of 'float'.])
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AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit],
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[Define as the bit index in the word where to find bit 0 of the exponent of 'float'.])
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;;
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esac
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])
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