[v3] Improve ratio_less

Index: testsuite/20_util/ratio/comparisons/comp1.cc
===================================================================
--- testsuite/20_util/ratio/comparisons/comp1.cc	(revision 162897)
+++ testsuite/20_util/ratio/comparisons/comp1.cc	(working copy)
@@ -1,7 +1,7 @@ 
 // { dg-options "-std=gnu++0x" }
 // { dg-require-cstdint "" }
 
-// Copyright (C) 2008, 2009 Free Software Foundation
+// Copyright (C) 2008, 2009, 2010 Free Software Foundation
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -45,7 +45,12 @@ 
   
   VERIFY( (std::ratio_less<std::ratio<1,3>, std::ratio<1,4>>::value == 0) );
   VERIFY( (std::ratio_less<std::ratio<1,3>, std::ratio<-1,3>>::value == 0) );
-      
+
+  VERIFY( (std::ratio_less<std::ratio<-1,3>, std::ratio<-1,4>>::value == 1) );
+  VERIFY( (std::ratio_less<std::ratio<0,4>, std::ratio<0,3>>::value == 0) );
+  VERIFY( (std::ratio_less<std::ratio<1,3>, std::ratio<0,3>>::value == 0) );
+  VERIFY( (std::ratio_less<std::ratio<0,3>, std::ratio<-1,4>>::value == 0) );
+
   VERIFY( (std::ratio_less_equal<std::ratio<-1,3>, 
            std::ratio<-1,3>>::value == 1) );
   VERIFY( ( std::ratio_less_equal<std::ratio<1,4>, 
Index: testsuite/20_util/ratio/comparisons/comp2.cc
===================================================================
--- testsuite/20_util/ratio/comparisons/comp2.cc	(revision 162897)
+++ testsuite/20_util/ratio/comparisons/comp2.cc	(working copy)
@@ -1,7 +1,7 @@ 
 // { dg-options "-std=gnu++0x" }
 // { dg-require-cstdint "" }
 
-// Copyright (C) 2008, 2009 Free Software Foundation
+// Copyright (C) 2008, 2009, 2010 Free Software Foundation
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -41,6 +41,13 @@ 
   
   VERIFY( (std::ratio_less<std::ratio<M - 1, M - 2>,
            std::ratio<-M, M - 1>>::value == 0) );
+
+  // No overflow
+  VERIFY( (std::ratio_less<std::ratio<M, M - 1>,
+           std::ratio<M, M - 2>>::value == 1) );
+
+  VERIFY( (std::ratio_less<std::ratio<-M, M - 1>,
+           std::ratio<-M, M - 2>>::value == 0) );
 }
 
 int main()
Index: include/std/ratio
===================================================================
--- include/std/ratio	(revision 162897)
+++ include/std/ratio	(working copy)
@@ -233,23 +233,30 @@ 
     struct ratio_not_equal
     : integral_constant<bool, !ratio_equal<_R1, _R2>::value>
     { };
-  
+
+  template<typename _R1>
+    struct __ratio_less_impl_1
+    : integral_constant<bool, _R1::num < _R1::den>
+    { }; 
+
+  template<typename _R1, typename _R2,
+	   bool = (_R1::num == 0 || _R2::num == 0
+		   || (__static_sign<_R1::num>::value
+		       != __static_sign<_R2::num>::value)),
+	   bool = (__static_sign<_R1::num>::value == -1
+		   && __static_sign<_R2::num>::value == -1)>
+    struct __ratio_less_impl
+    : __ratio_less_impl_1<typename ratio_divide<_R1, _R2>::type>::type
+    { };
+
   template<typename _R1, typename _R2>
-    struct __ratio_less_simple_impl
-    : integral_constant<bool,
-			(__safe_multiply<_R1::num, _R2::den>::value
-			 < __safe_multiply<_R2::num, _R1::den>::value)>
+    struct __ratio_less_impl<_R1, _R2, true, false>
+    : integral_constant<bool, _R1::num < _R2::num>
     { };
 
-  // If the denominators are equal or the signs differ, we can just compare
-  // numerators, otherwise fallback to the simple cross-multiply method.
   template<typename _R1, typename _R2>
-    struct __ratio_less_impl
-    : conditional<(_R1::den == _R2::den
-		   || (__static_sign<_R1::num>::value
-		       != __static_sign<_R2::num>::value)),
-      integral_constant<bool, (_R1::num < _R2::num)>,
-      __ratio_less_simple_impl<_R1, _R2>>::type
+    struct __ratio_less_impl<_R1, _R2, false, true>
+    : __ratio_less_impl_1<typename ratio_divide<_R2, _R1>::type>::type
     { };
 
   /// ratio_less