[base] Define CHECK comparison for signed vs. unsigned

src/base/logging.h

Index: src/base/logging.h
diff --git a/src/base/logging.h b/src/base/logging.h
index eae8a7fdb6aa68a5343a38936a3059128c451e2e..ac1cf5627e71b859cb52b91904ea446e19f3c7d7 100644
--- a/src/base/logging.h
+++ b/src/base/logging.h
@@ -115,21 +115,75 @@ DEFINE_MAKE_CHECK_OP_STRING(char const*)
 DEFINE_MAKE_CHECK_OP_STRING(void const*)
 #undef DEFINE_MAKE_CHECK_OP_STRING
 
+// is_signed_vs_unsigned::value is true if both types are integral, Lhs is
+// signed, and Rhs is unsigned. False in all other cases.
+template <typename Lhs, typename Rhs>
+struct is_signed_vs_unsigned {
+  enum : bool {
+    value = std::is_integral<Lhs>::value && std::is_integral<Rhs>::value &&
+            std::is_signed<Lhs>::value && std::is_unsigned<Rhs>::value
+  };
+};
+// Same thing, other way around: Lhs is unsigned, Rhs signed.
+template <typename Lhs, typename Rhs>
+struct is_unsigned_vs_signed : public is_signed_vs_unsigned<Rhs, Lhs> {};
+
+// Specialize the compare functions for signed vs. unsigned comparisons.
+// std::enable_if ensures that this template is only instantiable if both Lhs
+// and Rhs are integral types, and their signedness does not match.
+#define MAKE_UNSIGNED(Type, value) \
+  static_cast<typename std::make_unsigned<Type>::type>(value)
+#define DEFINE_SIGNED_MISMATCH_COMP(CHECK, NAME, IMPL)                  \
+  template <typename Lhs, typename Rhs>                                 \
+  V8_INLINE typename std::enable_if<CHECK<Lhs, Rhs>::value, bool>::type \
+      Cmp##NAME##Impl(Lhs const& lhs, Rhs const& rhs) {                 \
+    return IMPL;                                                        \
+  }
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, EQ,
+                            lhs >= 0 && MAKE_UNSIGNED(Lhs, lhs) == rhs)
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, LT,
+                            lhs < 0 || MAKE_UNSIGNED(Lhs, lhs) < rhs)
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, LE,
+                            lhs <= 0 || MAKE_UNSIGNED(Lhs, lhs) <= rhs)
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, NE, !CmpEQImpl(lhs, rhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, GT, !CmpLEImpl(lhs, rhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_signed_vs_unsigned, GE, !CmpLTImpl(lhs, rhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, EQ, CmpEQImpl(rhs, lhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, NE, CmpNEImpl(rhs, lhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, LT, CmpGTImpl(rhs, lhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, LE, CmpGEImpl(rhs, lhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, GT, CmpLTImpl(rhs, lhs))
+DEFINE_SIGNED_MISMATCH_COMP(is_unsigned_vs_signed, GE, CmpLEImpl(rhs, lhs))

[Igor Sheludko, 2016/11/24 15:37:12]

#undef DEFINE_SIGNED_MISMATCH_COMP

[Clemens Hammacher, 2016/11/24 17:06:30]

Oh, sure. And #undef MAKE_UNSIGNED. Done.

+
 // Helper functions for CHECK_OP macro.
 // The (float, float) and (double, double) instantiations are explicitly
-// externialized to ensure proper 32/64-bit comparisons on x86.
+// externalized to ensure proper 32/64-bit comparisons on x86.
+// The Cmp##NAME##Impl function is only instantiable if one of the two types is
+// not integral or their signedness matches (i.e. whenever no specialization is
+// required, see above). Otherwise it is disabled by the enable_if construct,
+// and the compiler will pick a specialization from above.
 #define DEFINE_CHECK_OP_IMPL(NAME, op)                                         \
   template <typename Lhs, typename Rhs>                                        \
+  V8_INLINE                                                                    \
+      typename std::enable_if<!is_signed_vs_unsigned<Lhs, Rhs>::value &&       \
+                                  !is_unsigned_vs_signed<Lhs, Rhs>::value,     \
+                              bool>::type                                      \
+          Cmp##NAME##Impl(typename PassType<Lhs>::type lhs,                    \
+                          typename PassType<Rhs>::type rhs) {                  \
+    return lhs op rhs;                                                         \
+  }                                                                            \
+  template <typename Lhs, typename Rhs>                                        \
   V8_INLINE std::string* Check##NAME##Impl(typename PassType<Lhs>::type lhs,   \
                                            typename PassType<Rhs>::type rhs,   \
                                            char const* msg) {                  \
-    return V8_LIKELY(lhs op rhs) ? nullptr                                     \
-                                 : MakeCheckOpString<Lhs, Rhs>(lhs, rhs, msg); \
+    bool cmp = Cmp##NAME##Impl<Lhs, Rhs>(lhs, rhs);                            \
+    return V8_LIKELY(cmp) ? nullptr                                            \
+                          : MakeCheckOpString<Lhs, Rhs>(lhs, rhs, msg);        \
   }                                                                            \
   extern template V8_BASE_EXPORT std::string* Check##NAME##Impl<float, float>( \
-      const float lhs, const float rhs, char const* msg);                      \
+      float lhs, float rhs, char const* msg);                                  \
   extern template V8_BASE_EXPORT std::string*                                  \
-      Check##NAME##Impl<double, double>(const double lhs, const double rhs,    \
+      Check##NAME##Impl<double, double>(double lhs, double rhs,                \
                                         char const* msg);
 DEFINE_CHECK_OP_IMPL(EQ, ==)
 DEFINE_CHECK_OP_IMPL(NE, !=)