diff -r 000000000000 -r 6474c204b198 mfbt/IntegerTypeTraits.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/IntegerTypeTraits.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,119 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Helpers to manipulate integer types that don't fit in TypeTraits.h */
+
+#ifndef mozilla_IntegerTypeTraits_h
+#define mozilla_IntegerTypeTraits_h
+
+#include "mozilla/TypeTraits.h"
+#include <stdint.h>
+
+namespace mozilla {
+
+namespace detail {
+
+/**
+ * StdintTypeForSizeAndSignedness returns the stdint integer type
+ * of given size (can be 1, 2, 4 or 8) and given signedness
+ * (false means unsigned, true means signed).
+ */
+template<size_t Size, bool Signedness>
+struct StdintTypeForSizeAndSignedness;
+
+template<>
+struct StdintTypeForSizeAndSignedness<1, true>
+{ typedef int8_t   Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<1, false>
+{ typedef uint8_t  Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<2, true>
+{ typedef int16_t  Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<2, false>
+{ typedef uint16_t Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<4, true>
+{ typedef int32_t  Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<4, false>
+{ typedef uint32_t Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<8, true>
+{ typedef int64_t  Type; };
+
+template<>
+struct StdintTypeForSizeAndSignedness<8, false>
+{ typedef uint64_t Type; };
+
+} // namespace detail
+
+template<size_t Size>
+struct UnsignedStdintTypeForSize
+  : detail::StdintTypeForSizeAndSignedness<Size, false>
+{};
+
+template<typename IntegerType>
+struct PositionOfSignBit
+{
+  static_assert(IsIntegral<IntegerType>::value, "PositionOfSignBit is only for integral types");
+  // 8 here should be CHAR_BIT from limits.h, but the world has moved on.
+  static const size_t value = 8 * sizeof(IntegerType) - 1;
+};
+
+/**
+ * MinValue returns the minimum value of the given integer type as a
+ * compile-time constant, which std::numeric_limits<IntegerType>::min()
+ * cannot do in c++98.
+ */
+template<typename IntegerType>
+struct MinValue
+{
+  private:
+    static_assert(IsIntegral<IntegerType>::value, "MinValue is only for integral types");
+
+    typedef typename MakeUnsigned<IntegerType>::Type UnsignedIntegerType;
+    static const size_t PosOfSignBit = PositionOfSignBit<IntegerType>::value;
+
+  public:
+    // Bitwise ops may return a larger type, that's why we cast explicitly.
+    // In C++, left bit shifts on signed values is undefined by the standard
+    // unless the shifted value is representable.
+    // Notice that signed-to-unsigned conversions are always well-defined in
+    // the standard as the value congruent to 2**n, as expected. By contrast,
+    // unsigned-to-signed is only well-defined if the value is representable.
+    static const IntegerType value =
+        IsSigned<IntegerType>::value
+        ? IntegerType(UnsignedIntegerType(1) << PosOfSignBit)
+        : IntegerType(0);
+};
+
+/**
+ * MaxValue returns the maximum value of the given integer type as a
+ * compile-time constant, which std::numeric_limits<IntegerType>::max()
+ * cannot do in c++98.
+ */
+template<typename IntegerType>
+struct MaxValue
+{
+    static_assert(IsIntegral<IntegerType>::value, "MaxValue is only for integral types");
+
+    // Tricksy, but covered by the CheckedInt unit test.
+    // Relies on the type of MinValue<IntegerType>::value
+    // being IntegerType.
+    static const IntegerType value = ~MinValue<IntegerType>::value;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_IntegerTypeTraits_h