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annotate m4/exponentl.m4 @ 29977:2bffa79ac8ee

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Move macros for finding floating-point exponents into separate M4 files.
author Ben Pfaff <blp@cs.stanford.edu>
date Wed, 23 Jul 2008 21:34:48 -0700
parents
children 90ea94356c75
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29977
2bffa79ac8ee Move macros for finding floating-point exponents into separate M4 files.
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1 # exponentl.m4 serial 1
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2 dnl Copyright (C) 2007-2008 Free Software Foundation, Inc.
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3 dnl This file is free software; the Free Software Foundation
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4 dnl gives unlimited permission to copy and/or distribute it,
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5 dnl with or without modifications, as long as this notice is preserved.
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6 AC_DEFUN([gl_LONG_DOUBLE_EXPONENT_LOCATION],
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7 [
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8 AC_REQUIRE([AC_C_BIGENDIAN])
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9 AC_CACHE_CHECK([where to find the exponent in a 'long double'],
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10 [gl_cv_cc_long_double_expbit0],
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11 [
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12 AC_TRY_RUN([
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13 #include <float.h>
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14 #include <stddef.h>
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15 #include <stdio.h>
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16 #include <string.h>
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17 #define NWORDS \
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18 ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
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19 typedef union { long double value; unsigned int word[NWORDS]; }
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20 memory_long_double;
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21 static unsigned int ored_words[NWORDS];
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22 static unsigned int anded_words[NWORDS];
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23 static void add_to_ored_words (long double x)
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24 {
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25 memory_long_double m;
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26 size_t i;
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27 /* Clear it first, in case
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28 sizeof (long double) < sizeof (memory_long_double). */
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29 memset (&m, 0, sizeof (memory_long_double));
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30 m.value = x;
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31 for (i = 0; i < NWORDS; i++)
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32 {
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33 ored_words[i] |= m.word[i];
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34 anded_words[i] &= m.word[i];
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35 }
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36 }
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37 int main ()
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38 {
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39 size_t j;
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40 FILE *fp = fopen ("conftest.out", "w");
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41 if (fp == NULL)
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42 return 1;
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43 for (j = 0; j < NWORDS; j++)
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44 anded_words[j] = ~ (unsigned int) 0;
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45 add_to_ored_words (0.25L);
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46 add_to_ored_words (0.5L);
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47 add_to_ored_words (1.0L);
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48 add_to_ored_words (2.0L);
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49 add_to_ored_words (4.0L);
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50 /* Remove bits that are common (e.g. if representation of the first mantissa
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51 bit is explicit). */
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52 for (j = 0; j < NWORDS; j++)
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53 ored_words[j] &= ~anded_words[j];
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54 /* Now find the nonzero word. */
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55 for (j = 0; j < NWORDS; j++)
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56 if (ored_words[j] != 0)
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57 break;
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58 if (j < NWORDS)
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59 {
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60 size_t i;
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61 for (i = j + 1; i < NWORDS; i++)
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62 if (ored_words[i] != 0)
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63 {
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64 fprintf (fp, "unknown");
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65 return (fclose (fp) != 0);
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66 }
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67 for (i = 0; ; i++)
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68 if ((ored_words[j] >> i) & 1)
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69 {
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70 fprintf (fp, "word %d bit %d", (int) j, (int) i);
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71 return (fclose (fp) != 0);
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72 }
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73 }
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74 fprintf (fp, "unknown");
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75 return (fclose (fp) != 0);
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76 }
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77 ],
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78 [gl_cv_cc_long_double_expbit0=`cat conftest.out`],
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79 [gl_cv_cc_long_double_expbit0="unknown"],
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80 [
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81 dnl When cross-compiling, we don't know. It depends on the
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82 dnl ABI and compiler version. There are too many cases.
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83 gl_cv_cc_long_double_expbit0="unknown"
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84 ])
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85 rm -f conftest.out
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86 ])
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87 case "$gl_cv_cc_long_double_expbit0" in
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88 word*bit*)
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89 word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
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90 bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'`
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91 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word],
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92 [Define as the word index where to find the exponent of 'long double'.])
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93 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit],
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94 [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.])
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95 ;;
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96 esac
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97 ])