Unordered/hash: Avoid a gcc warning. Refs #6771

[SVN r77832]

hash/test/Jamfile.v2

@@ -10,8 +10,8 @@ project hash-tests
         <warnings>all
         <toolset>intel:<warnings>on
         <toolset>intel:<cxxflags>-strict-ansi
-        <toolset>gcc:<cxxflags>"-pedantic -Wstrict-aliasing -fstrict-aliasing -Wextra -Wsign-promo -Wunused-parameter -Wconversion"
+        <toolset>gcc:<cxxflags>"-pedantic -Wstrict-aliasing -fstrict-aliasing -Wextra -Wsign-promo -Wunused-parameter -Wconversion -Wfloat-equal"
-        <toolset>darwin:<cxxflags>"-pedantic -Wstrict-aliasing -fstrict-aliasing -Wextra -Wsign-promo -Wunused-parameter -Wconversion"
+        <toolset>darwin:<cxxflags>"-pedantic -Wstrict-aliasing -fstrict-aliasing -Wextra -Wsign-promo -Wunused-parameter -Wconversion -Wfloat-equal"
         <toolset>msvc:<warnings-as-errors>on
         #<toolset>gcc:<warnings-as-errors>on
         #<toolset>darwin:<warnings-as-errors>on

hash/test/hash_complex_test.cpp

@@ -35,6 +35,10 @@ int main() {}
 #endif
 #endif
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+#endif
+
 #include <complex>
 #include <sstream>
 #include <boost/limits.hpp>

hash/test/hash_float_test.hpp

@@ -30,6 +30,10 @@
 #endif
 #endif
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+#endif
+
 char const* float_type(float*) { return "float"; }
 char const* float_type(double*) { return "double"; }
 char const* float_type(long double*) { return "long double"; }

hash/test/hash_number_test.cpp

@@ -28,6 +28,10 @@
 #pragma warning(disable:4310) // cast truncates constant value
 #endif
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wfloat-equal"
+#endif
+
 template <class T>
 void numeric_test(T*)
 {

include/boost/functional/hash/detail/hash_float.hpp

@@ -86,10 +86,24 @@ namespace boost
 {
     namespace hash_detail
     {
+        template <class T>
+        inline bool is_zero(T v)
+        {
+#if !defined(__GNUC__)
+            return v == 0;
+#else
+            // GCC's '-Wfloat-equal' will complain about comparing
+            // v to 0, but because it disables warnings for system
+            // headers it won't complain if you use std::equal_to to
+            // compare with 0. Resulting in this silliness:
+            return std::equal_to<T>()(v, 0);
+#endif
+        }
+
         template <class T>
         inline std::size_t float_hash_value(T v)
         {
-            return v == 0 ? 0 : float_hash_impl(v);
+            return boost::hash_detail::is_zero(v) ? 0 : float_hash_impl(v);
         }
     }
 }