--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2011-02-16  Paul Eggert  <eggert@cs.ucla.edu>
+
+	longlong: tune, particularly for common case of c99
+
+	* m4/longlong.m4 (AC_TYPE_LONG_LONG_INT): Don't bother compiling
+	or running anything if c99, or if unsigned long long int does not
+	work.  In either case, we know the answer without further tests.
+	Do not compile _AC_TYPE_LONG_LONG_SNIPPET twice.  Instead, compile
+	it at most once, and use its results for both long long int and
+	unsigned long long int.  This is more likely to be efficient in
+	the common case where the program wants to check for both long
+	long int and unsigned long long int.
+	(AC_TYPE_UNSIGNED_LONG_LONG_INT): Don't bother compiling if c99,
+	since the answer is already known.
+
 2011-02-15  Paul Eggert  <eggert@cs.ucla.edu>
 
 	getloadavg: set errno

--- a/m4/longlong.m4
+++ b/m4/longlong.m4
@@ -1,4 +1,4 @@
-# longlong.m4 serial 14
+# longlong.m4 serial 15
 dnl Copyright (C) 1999-2007, 2009-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,8 +7,8 @@
 dnl From Paul Eggert.
 
 # Define HAVE_LONG_LONG_INT if 'long long int' works.
-# This fixes a bug in Autoconf 2.61, but can be removed once we
-# assume 2.62 everywhere.
+# This fixes a bug in Autoconf 2.61, and can be faster
+# than what's in Autoconf 2.62 through 2.68.
 
 # Note: If the type 'long long int' exists but is only 32 bits large
 # (as on some very old compilers), HAVE_LONG_LONG_INT will not be
@@ -16,35 +16,38 @@
 
 AC_DEFUN([AC_TYPE_LONG_LONG_INT],
 [
+  AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
   AC_CACHE_CHECK([for long long int], [ac_cv_type_long_long_int],
-    [AC_LINK_IFELSE(
-       [_AC_TYPE_LONG_LONG_SNIPPET],
-       [dnl This catches a bug in Tandem NonStop Kernel (OSS) cc -O circa 2004.
-        dnl If cross compiling, assume the bug isn't important, since
-        dnl nobody cross compiles for this platform as far as we know.
-        AC_RUN_IFELSE(
-          [AC_LANG_PROGRAM(
-             [[@%:@include <limits.h>
-               @%:@ifndef LLONG_MAX
-               @%:@ define HALF \
-                        (1LL << (sizeof (long long int) * CHAR_BIT - 2))
-               @%:@ define LLONG_MAX (HALF - 1 + HALF)
-               @%:@endif]],
-             [[long long int n = 1;
-               int i;
-               for (i = 0; ; i++)
-                 {
-                   long long int m = n << i;
-                   if (m >> i != n)
-                     return 1;
-                   if (LLONG_MAX / 2 < m)
-                     break;
-                 }
-               return 0;]])],
-          [ac_cv_type_long_long_int=yes],
-          [ac_cv_type_long_long_int=no],
-          [ac_cv_type_long_long_int=yes])],
-       [ac_cv_type_long_long_int=no])])
+     [ac_cv_type_long_long_int=yes
+      if test "x${ac_cv_prog_cc_c99-no}" = xno; then
+        ac_cv_type_long_long_int=$ac_cv_type_unsigned_long_long_int
+        if test $ac_cv_type_long_long_int = yes; then
+          dnl Catch a bug in Tandem NonStop Kernel (OSS) cc -O circa 2004.
+          dnl If cross compiling, assume the bug is not important, since
+          dnl nobody cross compiles for this platform as far as we know.
+          AC_RUN_IFELSE(
+            [AC_LANG_PROGRAM(
+               [[@%:@include <limits.h>
+                 @%:@ifndef LLONG_MAX
+                 @%:@ define HALF \
+                          (1LL << (sizeof (long long int) * CHAR_BIT - 2))
+                 @%:@ define LLONG_MAX (HALF - 1 + HALF)
+                 @%:@endif]],
+               [[long long int n = 1;
+                 int i;
+                 for (i = 0; ; i++)
+                   {
+                     long long int m = n << i;
+                     if (m >> i != n)
+                       return 1;
+                     if (LLONG_MAX / 2 < m)
+                       break;
+                   }
+                 return 0;]])],
+            [],
+            [ac_cv_type_long_long_int=no])
+        fi
+      fi])
   if test $ac_cv_type_long_long_int = yes; then
     AC_DEFINE([HAVE_LONG_LONG_INT], [1],
       [Define to 1 if the system has the type `long long int'.])
@@ -52,8 +55,8 @@
 ])
 
 # Define HAVE_UNSIGNED_LONG_LONG_INT if 'unsigned long long int' works.
-# This fixes a bug in Autoconf 2.61, but can be removed once we
-# assume 2.62 everywhere.
+# This fixes a bug in Autoconf 2.61, and can be faster
+# than what's in Autoconf 2.62 through 2.68.
 
 # Note: If the type 'unsigned long long int' exists but is only 32 bits
 # large (as on some very old compilers), AC_TYPE_UNSIGNED_LONG_LONG_INT
@@ -64,10 +67,13 @@
 [
   AC_CACHE_CHECK([for unsigned long long int],
     [ac_cv_type_unsigned_long_long_int],
-    [AC_LINK_IFELSE(
-       [_AC_TYPE_LONG_LONG_SNIPPET],
-       [ac_cv_type_unsigned_long_long_int=yes],
-       [ac_cv_type_unsigned_long_long_int=no])])
+    [ac_cv_type_unsigned_long_long_int=yes
+     if test "x${ac_cv_prog_cc_c99-no}" = xno; then
+       AC_LINK_IFELSE(
+         [_AC_TYPE_LONG_LONG_SNIPPET],
+         [],
+         [ac_cv_type_unsigned_long_long_int=no])
+     fi])
   if test $ac_cv_type_unsigned_long_long_int = yes; then
     AC_DEFINE([HAVE_UNSIGNED_LONG_LONG_INT], [1],
       [Define to 1 if the system has the type `unsigned long long int'.])