1# round.m4 serial 23
2dnl Copyright (C) 2007, 2009-2021 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.
6
7AC_DEFUN([gl_FUNC_ROUND],
8[
9  m4_divert_text([DEFAULTS], [gl_round_required=plain])
10  AC_REQUIRE([gl_MATH_H_DEFAULTS])
11
12  dnl Persuade glibc <math.h> to declare round().
13  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
14
15  gl_CHECK_MATH_LIB([ROUND_LIBM], [x = round (x);],
16    [extern
17     #ifdef __cplusplus
18     "C"
19     #endif
20     double round (double);
21    ])
22  if test "$ROUND_LIBM" != missing; then
23    HAVE_ROUND=1
24    dnl Also check whether it's declared.
25    dnl IRIX 6.5 has round() in libm but doesn't declare it in <math.h>.
26    AC_CHECK_DECLS([round], , [HAVE_DECL_ROUND=0], [[#include <math.h>]])
27
28    dnl Test whether round() produces correct results. On NetBSD 3.0, for
29    dnl x = 1/2 - 2^-54, the system's round() returns a wrong result.
30    AC_REQUIRE([AC_PROG_CC])
31    AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
32    AC_CACHE_CHECK([whether round works], [gl_cv_func_round_works],
33      [
34        save_LIBS="$LIBS"
35        LIBS="$LIBS $ROUND_LIBM"
36        AC_RUN_IFELSE([AC_LANG_SOURCE([[
37#include <float.h>
38#include <math.h>
39extern
40#ifdef __cplusplus
41"C"
42#endif
43double round (double);
44#if defined _MSC_VER && !defined __clang__
45# pragma fenv_access (off)
46#endif
47int main()
48{
49  /* 2^DBL_MANT_DIG.  */
50  static const double TWO_MANT_DIG =
51    /* Assume DBL_MANT_DIG <= 5 * 31.
52       Use the identity
53       n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
54    (double) (1U << (DBL_MANT_DIG / 5))
55    * (double) (1U << ((DBL_MANT_DIG + 1) / 5))
56    * (double) (1U << ((DBL_MANT_DIG + 2) / 5))
57    * (double) (1U << ((DBL_MANT_DIG + 3) / 5))
58    * (double) (1U << ((DBL_MANT_DIG + 4) / 5));
59  volatile double x = 0.5 - 0.5 / TWO_MANT_DIG;
60  return (x < 0.5 && round (x) != 0.0);
61}]])], [gl_cv_func_round_works=yes], [gl_cv_func_round_works=no],
62        [case "$host_os" in
63           netbsd* | aix*) gl_cv_func_round_works="guessing no" ;;
64                           # Guess yes on MSVC, no on mingw.
65           mingw*)         AC_EGREP_CPP([Known], [
66#ifdef _MSC_VER
67 Known
68#endif
69                             ],
70                             [gl_cv_func_round_works="guessing yes"],
71                             [gl_cv_func_round_works="guessing no"])
72                           ;;
73           *)              gl_cv_func_round_works="guessing yes" ;;
74         esac
75        ])
76        LIBS="$save_LIBS"
77      ])
78    case "$gl_cv_func_round_works" in
79      *no) REPLACE_ROUND=1 ;;
80    esac
81
82    m4_ifdef([gl_FUNC_ROUND_IEEE], [
83      if test $gl_round_required = ieee && test $REPLACE_ROUND = 0; then
84        AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
85        AC_CACHE_CHECK([whether round works according to ISO C 99 with IEC 60559],
86          [gl_cv_func_round_ieee],
87          [
88            save_LIBS="$LIBS"
89            LIBS="$LIBS $ROUND_LIBM"
90            AC_RUN_IFELSE(
91              [AC_LANG_SOURCE([[
92#ifndef __NO_MATH_INLINES
93# define __NO_MATH_INLINES 1 /* for glibc */
94#endif
95#include <math.h>
96extern
97#ifdef __cplusplus
98"C"
99#endif
100double round (double);
101]gl_DOUBLE_MINUS_ZERO_CODE[
102]gl_DOUBLE_SIGNBIT_CODE[
103static double dummy (double f) { return 0; }
104int main (int argc, char *argv[])
105{
106  double (* volatile my_round) (double) = argc ? round : dummy;
107  /* Test whether round (-0.0) is -0.0.  */
108  if (signbitd (minus_zerod) && !signbitd (my_round (minus_zerod)))
109    return 1;
110  return 0;
111}
112              ]])],
113              [gl_cv_func_round_ieee=yes],
114              [gl_cv_func_round_ieee=no],
115              [case "$host_os" in
116                                # Guess yes on glibc systems.
117                 *-gnu* | gnu*) gl_cv_func_round_ieee="guessing yes" ;;
118                                # Guess yes on musl systems.
119                 *-musl*)       gl_cv_func_round_ieee="guessing yes" ;;
120                                # Guess yes on MSVC, no on mingw.
121                 mingw*)        AC_EGREP_CPP([Known], [
122#ifdef _MSC_VER
123 Known
124#endif
125                                  ],
126                                  [gl_cv_func_round_ieee="guessing yes"],
127                                  [gl_cv_func_round_ieee="guessing no"])
128                                ;;
129                                # If we don't know, obey --enable-cross-guesses.
130                 *)             gl_cv_func_round_ieee="$gl_cross_guess_normal" ;;
131               esac
132              ])
133            LIBS="$save_LIBS"
134          ])
135        case "$gl_cv_func_round_ieee" in
136          *yes) ;;
137          *) REPLACE_ROUND=1 ;;
138        esac
139      fi
140    ])
141  else
142    HAVE_ROUND=0
143    HAVE_DECL_ROUND=0
144  fi
145  if test $HAVE_ROUND = 0 || test $REPLACE_ROUND = 1; then
146    dnl Find libraries needed to link lib/round.c.
147    gl_FUNC_FLOOR_LIBS
148    gl_FUNC_CEIL_LIBS
149    ROUND_LIBM=
150    dnl Append $FLOOR_LIBM to ROUND_LIBM, avoiding gratuitous duplicates.
151    case " $ROUND_LIBM " in
152      *" $FLOOR_LIBM "*) ;;
153      *) ROUND_LIBM="$ROUND_LIBM $FLOOR_LIBM" ;;
154    esac
155    dnl Append $CEIL_LIBM to ROUND_LIBM, avoiding gratuitous duplicates.
156    case " $ROUND_LIBM " in
157      *" $CEIL_LIBM "*) ;;
158      *) ROUND_LIBM="$ROUND_LIBM $CEIL_LIBM" ;;
159    esac
160  fi
161  AC_SUBST([ROUND_LIBM])
162])
163