X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=m4%2Flogb.m4;h=11743a7d061543edb5870270cb789ff7b9562eb9;hb=79ca0976a6fd1773801ac0287a64cdf06aec7988;hp=c5b68032319d10e8c73f4433fe5c3fbdfba345ad;hpb=10d66aedfdd610f731c8c54152b9dfca3efbee12;p=gnulib.git

diff --git a/m4/logb.m4 b/m4/logb.m4
index c5b680323..11743a7d0 100644
--- a/m4/logb.m4
+++ b/m4/logb.m4
@@ -1,5 +1,5 @@
-# logb.m4 serial 1
-dnl Copyright (C) 2010 Free Software Foundation, Inc.
+# logb.m4 serial 6
+dnl Copyright (C) 2010-2014 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.
@@ -7,38 +7,119 @@ dnl with or without modifications, as long as this notice is preserved.
 AC_DEFUN([gl_FUNC_LOGB],
 [
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
+
+  dnl Persuade glibc <math.h> to declare logb().
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
   dnl Test whether logb() is declared.
-  AC_CHECK_DECLS([logb], , , [#include <math.h>])
+  AC_CHECK_DECLS([logb], , , [[#include <math.h>]])
   if test "$ac_cv_have_decl_logb" != yes; then
     HAVE_DECL_LOGB=0
   fi
   dnl Test whether logb() can be used without libm.
   LOGB_LIBM=?
-  AC_TRY_LINK([
-     #ifndef __NO_MATH_INLINES
-     # define __NO_MATH_INLINES 1 /* for glibc */
-     #endif
-     #include <math.h>
-     extern double logb (double x);
-     double x;],
-    [x = logb(x);],
+  AC_LINK_IFELSE(
+    [AC_LANG_PROGRAM(
+       [[#ifndef __NO_MATH_INLINES
+         # define __NO_MATH_INLINES 1 /* for glibc */
+         #endif
+         #include <math.h>
+         extern
+         #ifdef __cplusplus
+         "C"
+         #endif
+         double logb (double x);
+         double x;]],
+       [[x = logb(x);]])],
     [LOGB_LIBM=])
   if test "$LOGB_LIBM" = "?"; then
     save_LIBS="$LIBS"
     LIBS="$LIBS -lm"
-    AC_TRY_LINK([
-       #ifndef __NO_MATH_INLINES
-       # define __NO_MATH_INLINES 1 /* for glibc */
-       #endif
-       #include <math.h>
-       extern double logb (double x);
-       double x;],
-      [x = logb(x);],
+    AC_LINK_IFELSE(
+      [AC_LANG_PROGRAM(
+         [[#ifndef __NO_MATH_INLINES
+           # define __NO_MATH_INLINES 1 /* for glibc */
+           #endif
+           #include <math.h>
+           extern
+           #ifdef __cplusplus
+           "C"
+           #endif
+           double logb (double x);
+           double x;]],
+         [[x = logb(x);]])],
       [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
+        ])
+    ])
+])