-# logb.m4 serial 5
+# logb.m4 serial 6
dnl Copyright (C) 2010-2012 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
[LOGB_LIBM="-lm"])
LIBS="$save_LIBS"
fi
- if test "$LOGB_LIBM" = "?"; then
+ if test "$LOGB_LIBM" != "?"; then
+ HAVE_LOGB=1
+ save_LIBS="$LIBS"
+ LIBS="$LIBS $LOGB_LIBM"
+ gl_FUNC_LOGB_WORKS
+ LIBS="$save_LIBS"
+ case "$gl_cv_func_logb_works" in
+ *yes) ;;
+ *) REPLACE_LOGB=1 ;;
+ esac
+ else
+ HAVE_LOGB=0
+ fi
+ if test $HAVE_LOGB = 0 || test $REPLACE_LOGB = 1; then
+ dnl Find libraries needed to link lib/logb.c.
+ AC_REQUIRE([gl_FUNC_FREXP])
+ AC_REQUIRE([gl_FUNC_ISNAND])
LOGB_LIBM=
+ dnl Append $FREXP_LIBM to LOGB_LIBM, avoiding gratuitous duplicates.
+ case " $LOGB_LIBM " in
+ *" $FREXP_LIBM "*) ;;
+ *) LOGB_LIBM="$LOGB_LIBM $FREXP_LIBM" ;;
+ esac
+ dnl Append $ISNAND_LIBM to LOGB_LIBM, avoiding gratuitous duplicates.
+ case " $LOGB_LIBM " in
+ *" $ISNAND_LIBM "*) ;;
+ *) LOGB_LIBM="$LOGB_LIBM $ISNAND_LIBM" ;;
+ esac
fi
AC_SUBST([LOGB_LIBM])
])
+
+dnl Test whether logb() works.
+dnl On glibc 2.11/ppc, glibc 2.7/sparc, glibc 2.7/hppa, Solaris 10/SPARC,
+dnl Cygwin 1.5.x, the return value for subnormal (denormalized) arguments is
+dnl too large.
+AC_DEFUN([gl_FUNC_LOGB_WORKS],
+[
+ AC_REQUIRE([AC_PROG_CC])
+ AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+ AC_CACHE_CHECK([whether logb works], [gl_cv_func_logb_works],
+ [
+ AC_RUN_IFELSE(
+ [AC_LANG_SOURCE([[
+#include <float.h>
+#include <math.h>
+extern
+#ifdef __cplusplus
+"C"
+#endif
+double logb (double);
+volatile double x;
+int main ()
+{
+ int i;
+ for (i = 1, x = 1.0; i >= DBL_MIN_EXP; i--, x *= 0.5)
+ ;
+ /* Here i = DBL_MIN_EXP - 1. Either x = 2^(i-1) is subnormal or x = 0.0. */
+ if (x > 0.0 && !(logb (x) == (double)(i - 1)))
+ return 1;
+ return 0;
+}
+]])],
+ [gl_cv_func_logb_works=yes],
+ [gl_cv_func_logb_works=no],
+ [case "$host_os" in
+ *gnu* | solaris* | cygwin*) gl_cv_func_logb_works="guessing no";;
+ *) gl_cv_func_logb_works="guessing yes";;
+ esac
+ ])
+ ])
+])