1 # exponentf.m4 serial 1
2 dnl Copyright (C) 2007-2010 Free Software Foundation, Inc.
3 dnl This file is free software; the Free Software Foundation
4 dnl gives unlimited permission to copy and/or distribute it,
5 dnl with or without modifications, as long as this notice is preserved.
6 AC_DEFUN([gl_FLOAT_EXPONENT_LOCATION],
8 AC_CACHE_CHECK([where to find the exponent in a 'float'],
9 [gl_cv_cc_float_expbit0],
17 ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
18 typedef union { float value; unsigned int word[NWORDS]; } memory_float;
19 static unsigned int ored_words[NWORDS];
20 static unsigned int anded_words[NWORDS];
21 static void add_to_ored_words (float x)
25 /* Clear it first, in case
26 sizeof (float) < sizeof (memory_float). */
27 memset (&m, 0, sizeof (memory_float));
29 for (i = 0; i < NWORDS; i++)
31 ored_words[i] |= m.word[i];
32 anded_words[i] &= m.word[i];
38 FILE *fp = fopen ("conftest.out", "w");
41 for (j = 0; j < NWORDS; j++)
42 anded_words[j] = ~ (unsigned int) 0;
43 add_to_ored_words (0.25f);
44 add_to_ored_words (0.5f);
45 add_to_ored_words (1.0f);
46 add_to_ored_words (2.0f);
47 add_to_ored_words (4.0f);
48 /* Remove bits that are common (e.g. if representation of the first mantissa
50 for (j = 0; j < NWORDS; j++)
51 ored_words[j] &= ~anded_words[j];
52 /* Now find the nonzero word. */
53 for (j = 0; j < NWORDS; j++)
54 if (ored_words[j] != 0)
59 for (i = j + 1; i < NWORDS; i++)
60 if (ored_words[i] != 0)
62 fprintf (fp, "unknown");
63 return (fclose (fp) != 0);
66 if ((ored_words[j] >> i) & 1)
68 fprintf (fp, "word %d bit %d", (int) j, (int) i);
69 return (fclose (fp) != 0);
72 fprintf (fp, "unknown");
73 return (fclose (fp) != 0);
76 [gl_cv_cc_float_expbit0=`cat conftest.out`],
77 [gl_cv_cc_float_expbit0="unknown"],
78 [gl_cv_cc_float_expbit0="word 0 bit 23"])
81 case "$gl_cv_cc_float_expbit0" in
83 word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
84 bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'`
85 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word],
86 [Define as the word index where to find the exponent of 'float'.])
87 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit],
88 [Define as the bit index in the word where to find bit 0 of the exponent of 'float'.])