1# exponentd.m4 serial 3
2dnl Copyright (C) 2007-2008, 2010-2021 Free Software Foundation, Inc.
3dnl This file is free software; the Free Software Foundation
4dnl gives unlimited permission to copy and/or distribute it,
5dnl with or without modifications, as long as this notice is preserved.
6AC_DEFUN([gl_DOUBLE_EXPONENT_LOCATION],
7[
8  AC_CACHE_CHECK([where to find the exponent in a 'double'],
9    [gl_cv_cc_double_expbit0],
10    [
11      AC_RUN_IFELSE(
12        [AC_LANG_SOURCE([[
13#include <float.h>
14#include <stddef.h>
15#include <stdio.h>
16#include <string.h>
17#define NWORDS \
18  ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
19typedef union { double value; unsigned int word[NWORDS]; } memory_double;
20static unsigned int ored_words[NWORDS];
21static unsigned int anded_words[NWORDS];
22static void add_to_ored_words (double x)
23{
24  memory_double m;
25  size_t i;
26  /* Clear it first, in case sizeof (double) < sizeof (memory_double).  */
27  memset (&m, 0, sizeof (memory_double));
28  m.value = x;
29  for (i = 0; i < NWORDS; i++)
30    {
31      ored_words[i] |= m.word[i];
32      anded_words[i] &= m.word[i];
33    }
34}
35int main ()
36{
37  size_t j;
38  FILE *fp = fopen ("conftest.out", "w");
39  if (fp == NULL)
40    return 1;
41  for (j = 0; j < NWORDS; j++)
42    anded_words[j] = ~ (unsigned int) 0;
43  add_to_ored_words (0.25);
44  add_to_ored_words (0.5);
45  add_to_ored_words (1.0);
46  add_to_ored_words (2.0);
47  add_to_ored_words (4.0);
48  /* Remove bits that are common (e.g. if representation of the first mantissa
49     bit is explicit).  */
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)
55      break;
56  if (j < NWORDS)
57    {
58      size_t i;
59      for (i = j + 1; i < NWORDS; i++)
60        if (ored_words[i] != 0)
61          {
62            fprintf (fp, "unknown");
63            return (fclose (fp) != 0);
64          }
65      for (i = 0; ; i++)
66        if ((ored_words[j] >> i) & 1)
67          {
68            fprintf (fp, "word %d bit %d", (int) j, (int) i);
69            return (fclose (fp) != 0);
70          }
71    }
72  fprintf (fp, "unknown");
73  return (fclose (fp) != 0);
74}
75        ]])],
76        [gl_cv_cc_double_expbit0=`cat conftest.out`],
77        [gl_cv_cc_double_expbit0="unknown"],
78        [
79          dnl On ARM, there are two 'double' floating-point formats, used by
80          dnl different sets of instructions: The older FPA instructions assume
81          dnl that they are stored in big-endian word order, while the words
82          dnl (like integer types) are stored in little-endian byte order.
83          dnl The newer VFP instructions assume little-endian order
84          dnl consistently.
85          AC_EGREP_CPP([mixed_endianness], [
86#if defined arm || defined __arm || defined __arm__
87  mixed_endianness
88#endif
89            ],
90            [gl_cv_cc_double_expbit0="unknown"],
91            [
92              pushdef([AC_MSG_CHECKING],[:])dnl
93              pushdef([AC_MSG_RESULT],[:])dnl
94              pushdef([AC_MSG_RESULT_UNQUOTED],[:])dnl
95              AC_C_BIGENDIAN(
96                [gl_cv_cc_double_expbit0="word 0 bit 20"],
97                [gl_cv_cc_double_expbit0="word 1 bit 20"],
98                [gl_cv_cc_double_expbit0="unknown"])
99              popdef([AC_MSG_RESULT_UNQUOTED])dnl
100              popdef([AC_MSG_RESULT])dnl
101              popdef([AC_MSG_CHECKING])dnl
102            ])
103        ])
104      rm -f conftest.out
105    ])
106  case "$gl_cv_cc_double_expbit0" in
107    word*bit*)
108      word=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
109      bit=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word.*bit //'`
110      AC_DEFINE_UNQUOTED([DBL_EXPBIT0_WORD], [$word],
111        [Define as the word index where to find the exponent of 'double'.])
112      AC_DEFINE_UNQUOTED([DBL_EXPBIT0_BIT], [$bit],
113        [Define as the bit index in the word where to find bit 0 of the exponent of 'double'.])
114      ;;
115  esac
116])
117