1 files changed, 143 insertions, 0 deletions
diff --git a/mfbt/IntegerTypeTraits.h b/mfbt/IntegerTypeTraits.h
new file mode 100644
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+++ b/mfbt/IntegerTypeTraits.h
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+/* -*- 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<size_t Size>
+struct SignedStdintTypeForSize
+  : detail::StdintTypeForSizeAndSignedness<Size, true>
+{};
+
+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