X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=m4%2Flog2.m4;h=4e093ce0dc368013d0b1ffeda2b08d10fc0a6686;hb=43593319b31e6b0175b8eec4433bac744959822d;hp=f8ef24bdd639593c4fc357d5424497843f452aff;hpb=6d131d20837bfac5a0c48692485debf3b28bfae2;p=gnulib.git

diff --git a/m4/log2.m4 b/m4/log2.m4
index f8ef24bdd..4e093ce0d 100644
--- a/m4/log2.m4
+++ b/m4/log2.m4
@@ -1,11 +1,12 @@
-# log2.m4 serial 1
-dnl Copyright (C) 2010-2012 Free Software Foundation, Inc.
+# log2.m4 serial 3
+dnl Copyright (C) 2010-2013 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_LOG2],
 [
+  m4_divert_text([DEFAULTS], [gl_log2_required=plain])
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
 
   dnl Persuade glibc <math.h> to declare log2().
@@ -33,6 +34,65 @@ AC_DEFUN([gl_FUNC_LOG2],
       *yes) ;;
       *) REPLACE_LOG2=1 ;;
     esac
+
+    m4_ifdef([gl_FUNC_LOG2_IEEE], [
+      if test $gl_log2_required = ieee && test $REPLACE_LOG2 = 0; then
+        AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+        AC_CACHE_CHECK([whether log2 works according to ISO C 99 with IEC 60559],
+          [gl_cv_func_log2_ieee],
+          [
+            save_LIBS="$LIBS"
+            LIBS="$LIBS $LOG2_LIBM"
+            AC_RUN_IFELSE(
+              [AC_LANG_SOURCE([[
+#ifndef __NO_MATH_INLINES
+# define __NO_MATH_INLINES 1 /* for glibc */
+#endif
+#include <math.h>
+#ifndef log2 /* for Cygwin 1.7.x */
+extern
+#ifdef __cplusplus
+"C"
+#endif
+double log2 (double);
+#endif
+/* Compare two numbers with ==.
+   This is a separate function because IRIX 6.5 "cc -O" miscompiles an
+   'x == x' test.  */
+static int
+numeric_equal (double x, double y)
+{
+  return x == y;
+}
+static double dummy (double x) { return 0; }
+int main (int argc, char *argv[])
+{
+  double (*my_log2) (double) = argc ? log2 : dummy;
+  /* Test log2(negative).
+     This test fails on NetBSD 5.1 and Solaris 11 2011-11.  */
+  double y = my_log2 (-1.0);
+  if (numeric_equal (y, y))
+    return 1;
+  return 0;
+}
+              ]])],
+              [gl_cv_func_log2_ieee=yes],
+              [gl_cv_func_log2_ieee=no],
+              [case "$host_os" in
+                         # Guess yes on glibc systems.
+                 *-gnu*) gl_cv_func_log2_ieee="guessing yes" ;;
+                         # If we don't know, assume the worst.
+                 *)      gl_cv_func_log2_ieee="guessing no" ;;
+               esac
+              ])
+            LIBS="$save_LIBS"
+          ])
+        case "$gl_cv_func_log2_ieee" in
+          *yes) ;;
+          *) REPLACE_LOG2=1 ;;
+        esac
+      fi
+    ])
   else
     HAVE_LOG2=0
     HAVE_DECL_LOG2=0