round.m4 2.15 KB
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# round.m4 serial 5
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dnl Copyright (C) 2007 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_ROUND],
[
  AC_REQUIRE([gl_MATH_H_DEFAULTS])
  dnl Persuade glibc <math.h> to declare round().
  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
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  AC_CHECK_DECLS([round], , , [#include <math.h>])
  if test "$ac_cv_have_decl_round" = yes; then
    gl_CHECK_MATH_LIB([ROUND_LIBM], [x = round (x);])
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  fi
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  if test "$ac_cv_have_decl_round" = yes && test "$ROUND_LIBM" != missing; then
    dnl Test whether round() produces correct results. On NetBSD 3.0, for
    dnl x = 1/2 - 2^-54, the system's round() returns a wrong result.
    AC_REQUIRE([AC_PROG_CC])
    AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
    AC_CACHE_CHECK([whether round works], [gl_cv_func_round_works],
      [
        save_LIBS="$LIBS"
        LIBS="$LIBS $ROUND_LIBM"
        AC_TRY_RUN([
#include <float.h>
#include <math.h>
int main()
{
  /* 2^DBL_MANT_DIG.  */
  static const double TWO_MANT_DIG =
    /* Assume DBL_MANT_DIG <= 5 * 31.
       Use the identity
       n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
    (double) (1U << (DBL_MANT_DIG / 5))
    * (double) (1U << ((DBL_MANT_DIG + 1) / 5))
    * (double) (1U << ((DBL_MANT_DIG + 2) / 5))
    * (double) (1U << ((DBL_MANT_DIG + 3) / 5))
    * (double) (1U << ((DBL_MANT_DIG + 4) / 5));
  volatile double x = 0.5 - 0.5 / TWO_MANT_DIG;
  exit (x < 0.5 && round (x) != 0.0);
}], [gl_cv_func_round_works=yes], [gl_cv_func_round_works=no],
        [case "$host_os" in
           netbsd*) gl_cv_func_round_works="guessing no";;
           *)       gl_cv_func_round_works="guessing yes";;
         esac
        ])
        LIBS="$save_LIBS"
      ])
    case "$gl_cv_func_round_works" in
      *no) ROUND_LIBM=missing ;;
    esac
  fi
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  if test "$ac_cv_have_decl_round" != yes || test "$ROUND_LIBM" = missing; then
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    REPLACE_ROUND=1
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    AC_LIBOBJ([round])
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    gl_FUNC_FLOOR_LIBS
    gl_FUNC_CEIL_LIBS
    ROUND_LIBM="$FLOOR_LIBM $CEIL_LIBM"
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  fi
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  AC_SUBST([ROUND_LIBM])
])