3 dnl Copyright (C) 2007-2008, 2010-2024 Free Software Foundation, Inc.
4 dnl This file is free software; the Free Software Foundation
5 dnl gives unlimited permission to copy and/or distribute it,
6 dnl with or without modifications, as long as this notice is preserved.
7 AC_DEFUN_ONCE([gl_FLOAT_EXPONENT_LOCATION],
9 AC_CACHE_CHECK([where to find the exponent in a 'float'],
10 [gl_cv_cc_float_expbit0],
19 ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
20 typedef union { float value; unsigned int word[NWORDS]; } memory_float;
21 static unsigned int ored_words[NWORDS];
22 static unsigned int anded_words[NWORDS];
23 static void add_to_ored_words (float x)
27 /* Clear it first, in case
28 sizeof (float) < sizeof (memory_float). */
29 memset (&m, 0, sizeof (memory_float));
31 for (i = 0; i < NWORDS; i++)
33 ored_words[i] |= m.word[i];
34 anded_words[i] &= m.word[i];
40 FILE *fp = fopen ("conftest.out", "w");
43 for (j = 0; j < NWORDS; j++)
44 anded_words[j] = ~ (unsigned int) 0;
45 add_to_ored_words (0.25f);
46 add_to_ored_words (0.5f);
47 add_to_ored_words (1.0f);
48 add_to_ored_words (2.0f);
49 add_to_ored_words (4.0f);
50 /* Remove bits that are common (e.g. if representation of the first mantissa
52 for (j = 0; j < NWORDS; j++)
53 ored_words[j] &= ~anded_words[j];
54 /* Now find the nonzero word. */
55 for (j = 0; j < NWORDS; j++)
56 if (ored_words[j] != 0)
61 for (i = j + 1; i < NWORDS; i++)
62 if (ored_words[i] != 0)
64 fprintf (fp, "unknown");
65 return (fclose (fp) != 0);
68 if ((ored_words[j] >> i) & 1)
70 fprintf (fp, "word %d bit %d", (int) j, (int) i);
71 return (fclose (fp) != 0);
74 fprintf (fp, "unknown");
75 return (fclose (fp) != 0);
78 [gl_cv_cc_float_expbit0=`cat conftest.out`],
79 [gl_cv_cc_float_expbit0="unknown"],
80 [gl_cv_cc_float_expbit0="word 0 bit 23"])
83 case "$gl_cv_cc_float_expbit0" in
85 word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
86 bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'`
87 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word],
88 [Define as the word index where to find the exponent of 'float'.])
89 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit],
90 [Define as the bit index in the word where to find bit 0 of the exponent of 'float'.])