Fix warnings about signed/unsigned comparisons inside wxMax() and friends.

wxMax, wxMin and wxClip work correctly when called with a mix of signed and
unsigned arguments but give warnings about comparing them when compiled with
g++.

Cast both arguments to the result type, which is defined consistently with
standard C rules for implicit promotion, before comparing them to avoid this.

Also add more tests to check that using these functions in this case doesn't
provoke warnings.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65933 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/utils.h

@@ -63,21 +63,35 @@ template<typename T1, typename T2>
 inline typename wxImplicitConversionType<T1,T2>::value
 wxMax(T1 a, T2 b)
 {
-    return (a > b) ? a : b;
+    typedef typename wxImplicitConversionType<T1,T2>::value ResultType;
+
+    // Cast both operands to the same type before comparing them to avoid
+    // warnings about signed/unsigned comparisons from some compilers:
+    return static_cast<ResultType>(a) > static_cast<ResultType>(b) ? a : b;
 }
 
 template<typename T1, typename T2>
 inline typename wxImplicitConversionType<T1,T2>::value
 wxMin(T1 a, T2 b)
 {
-    return (a < b) ? a : b;
+    typedef typename wxImplicitConversionType<T1,T2>::value ResultType;
+
+    return static_cast<ResultType>(a) < static_cast<ResultType>(b) ? a : b;
 }
 
 template<typename T1, typename T2, typename T3>
 inline typename wxImplicitConversionType3<T1,T2,T3>::value
 wxClip(T1 a, T2 b, T3 c)
 {
-    return (a < b) ? b : ((a > c) ? c : a);
+    typedef typename wxImplicitConversionType3<T1,T2,T3>::value ResultType;
+
+    if ( static_cast<ResultType>(a) < static_cast<ResultType>(b) )
+        return b;
+
+    if ( static_cast<ResultType>(a) > static_cast<ResultType>(c) )
+        return c;
+
+    return a;
 }
 
 // ----------------------------------------------------------------------------

tests/misc/metatest.cpp

@@ -36,11 +36,13 @@ private:
         CPPUNIT_TEST( IsPod );
         CPPUNIT_TEST( IsMovable );
         CPPUNIT_TEST( ImplicitConversion );
+        CPPUNIT_TEST( MinMax );
     CPPUNIT_TEST_SUITE_END();
 
     void IsPod();
     void IsMovable();
     void ImplicitConversion();
+    void MinMax();
 
     DECLARE_NO_COPY_CLASS(MetaProgrammingTestCase)
 };
@@ -77,13 +79,6 @@ void MetaProgrammingTestCase::IsMovable()
 
 void MetaProgrammingTestCase::ImplicitConversion()
 {
-    // wxImplicitConversionType<> is used to implement wxMax(). We test it
-    // indirectly through that here.
-
-    // test that wxMax(1.1,1) returns float, not long int
-    float f = wxMax(1.1f, 1l);
-    CPPUNIT_ASSERT_EQUAL( 1.1f, f);
-
 #ifndef wxNO_RTTI
     CPPUNIT_ASSERT(typeid(wxImplicitConversionType<char,int>::value) == typeid(int));
     CPPUNIT_ASSERT(typeid(wxImplicitConversionType<int,unsigned>::value) == typeid(unsigned));
@@ -92,3 +87,19 @@ void MetaProgrammingTestCase::ImplicitConversion()
 #endif
 #endif // !wxNO_RTTI
 }
+
+void MetaProgrammingTestCase::MinMax()
+{
+    // test that wxMax(1.1,1) returns float, not long int
+    float f = wxMax(1.1f, 1l);
+    CPPUNIT_ASSERT_EQUAL( 1.1f, f);
+
+    // test that comparing signed and unsigned correctly returns unsigned: this
+    // may seem counterintuitive in this case but this is consistent with the
+    // standard C conversions
+    CPPUNIT_ASSERT_EQUAL( 1, wxMin(-1, 1u) );
+
+    CPPUNIT_ASSERT_EQUAL( -1., wxClip(-1.5, -1, 1) );
+    CPPUNIT_ASSERT_EQUAL( 0, wxClip(0, -1, 1) );
+    CPPUNIT_ASSERT_EQUAL( 1, wxClip(2l, -1, 1) );
+}