3 dnl Copyright (C) 2007-2024 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_LONG_DOUBLE_EXPONENT_LOCATION],
9 AC_REQUIRE([gl_BIGENDIAN])
10 AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
11 AC_CACHE_CHECK([where to find the exponent in a 'long double'],
12 [gl_cv_cc_long_double_expbit0],
21 ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
22 typedef union { long double value; unsigned int word[NWORDS]; }
24 static unsigned int ored_words[NWORDS];
25 static unsigned int anded_words[NWORDS];
26 static void add_to_ored_words (long double *x)
30 /* Clear it first, in case
31 sizeof (long double) < sizeof (memory_long_double). */
32 memset (&m, 0, sizeof (memory_long_double));
34 for (i = 0; i < NWORDS; i++)
36 ored_words[i] |= m.word[i];
37 anded_words[i] &= m.word[i];
42 static long double samples[5] = { 0.25L, 0.5L, 1.0L, 2.0L, 4.0L };
44 FILE *fp = fopen ("conftest.out", "w");
47 for (j = 0; j < NWORDS; j++)
48 anded_words[j] = ~ (unsigned int) 0;
49 for (j = 0; j < 5; j++)
50 add_to_ored_words (&samples[j]);
51 /* Remove bits that are common (e.g. if representation of the first mantissa
53 for (j = 0; j < NWORDS; j++)
54 ored_words[j] &= ~anded_words[j];
55 /* Now find the nonzero word. */
56 for (j = 0; j < NWORDS; j++)
57 if (ored_words[j] != 0)
62 for (i = j + 1; i < NWORDS; i++)
63 if (ored_words[i] != 0)
65 fprintf (fp, "unknown");
66 return (fclose (fp) != 0);
69 if ((ored_words[j] >> i) & 1)
71 fprintf (fp, "word %d bit %d", (int) j, (int) i);
72 return (fclose (fp) != 0);
75 fprintf (fp, "unknown");
76 return (fclose (fp) != 0);
79 [gl_cv_cc_long_double_expbit0=`cat conftest.out`],
80 [gl_cv_cc_long_double_expbit0="unknown"],
82 dnl When cross-compiling, in general we don't know. It depends on the
83 dnl ABI and compiler version. There are too many cases.
84 gl_cv_cc_long_double_expbit0="unknown"
87 # On native Windows (little-endian), we know the result
88 # in two cases: mingw, MSVC.
89 AC_EGREP_CPP([Known], [
93 ], [gl_cv_cc_long_double_expbit0="word 2 bit 0"])
94 AC_EGREP_CPP([Known], [
98 ], [gl_cv_cc_long_double_expbit0="word 1 bit 20"])
104 case "$gl_cv_cc_long_double_expbit0" in
106 word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
107 bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'`
108 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word],
109 [Define as the word index where to find the exponent of 'long double'.])
110 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit],
111 [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.])