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- /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
- /* 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/. */
- /* Cast operations to supplement the built-in casting operations. */
- #ifndef mozilla_Casting_h
- #define mozilla_Casting_h
- #include "mozilla/Assertions.h"
- #include "mozilla/TypeTraits.h"
- #include <limits.h>
- namespace mozilla {
- /**
- * Sets the outparam value of type |To| with the same underlying bit pattern of
- * |aFrom|.
- *
- * |To| and |From| must be types of the same size; be careful of cross-platform
- * size differences, or this might fail to compile on some but not all
- * platforms.
- *
- * There is also a variant that returns the value directly. In most cases, the
- * two variants should be identical. However, in the specific case of x86
- * chips, the behavior differs: returning floating-point values directly is done
- * through the x87 stack, and x87 loads and stores turn signaling NaNs into
- * quiet NaNs... silently. Returning floating-point values via outparam,
- * however, is done entirely within the SSE registers when SSE2 floating-point
- * is enabled in the compiler, which has semantics-preserving behavior you would
- * expect.
- *
- * If preserving the distinction between signaling NaNs and quiet NaNs is
- * important to you, you should use the outparam version. In all other cases,
- * you should use the direct return version.
- */
- template<typename To, typename From>
- inline void
- BitwiseCast(const From aFrom, To* aResult)
- {
- static_assert(sizeof(From) == sizeof(To),
- "To and From must have the same size");
- union
- {
- From mFrom;
- To mTo;
- } u;
- u.mFrom = aFrom;
- *aResult = u.mTo;
- }
- template<typename To, typename From>
- inline To
- BitwiseCast(const From aFrom)
- {
- To temp;
- BitwiseCast<To, From>(aFrom, &temp);
- return temp;
- }
- namespace detail {
- enum ToSignedness { ToIsSigned, ToIsUnsigned };
- enum FromSignedness { FromIsSigned, FromIsUnsigned };
- template<typename From,
- typename To,
- FromSignedness = IsSigned<From>::value ? FromIsSigned : FromIsUnsigned,
- ToSignedness = IsSigned<To>::value ? ToIsSigned : ToIsUnsigned>
- struct BoundsCheckImpl;
- // Implicit conversions on operands to binary operations make this all a bit
- // hard to verify. Attempt to ease the pain below by *only* comparing values
- // that are obviously the same type (and will undergo no further conversions),
- // even when it's not strictly necessary, for explicitness.
- enum UUComparison { FromIsBigger, FromIsNotBigger };
- // Unsigned-to-unsigned range check
- template<typename From, typename To,
- UUComparison = (sizeof(From) > sizeof(To))
- ? FromIsBigger
- : FromIsNotBigger>
- struct UnsignedUnsignedCheck;
- template<typename From, typename To>
- struct UnsignedUnsignedCheck<From, To, FromIsBigger>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return aFrom <= From(To(-1));
- }
- };
- template<typename From, typename To>
- struct UnsignedUnsignedCheck<From, To, FromIsNotBigger>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return true;
- }
- };
- template<typename From, typename To>
- struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsUnsigned>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return UnsignedUnsignedCheck<From, To>::checkBounds(aFrom);
- }
- };
- // Signed-to-unsigned range check
- template<typename From, typename To>
- struct BoundsCheckImpl<From, To, FromIsSigned, ToIsUnsigned>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- if (aFrom < 0) {
- return false;
- }
- if (sizeof(To) >= sizeof(From)) {
- return true;
- }
- return aFrom <= From(To(-1));
- }
- };
- // Unsigned-to-signed range check
- enum USComparison { FromIsSmaller, FromIsNotSmaller };
- template<typename From, typename To,
- USComparison = (sizeof(From) < sizeof(To))
- ? FromIsSmaller
- : FromIsNotSmaller>
- struct UnsignedSignedCheck;
- template<typename From, typename To>
- struct UnsignedSignedCheck<From, To, FromIsSmaller>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return true;
- }
- };
- template<typename From, typename To>
- struct UnsignedSignedCheck<From, To, FromIsNotSmaller>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- const To MaxValue = To((1ULL << (CHAR_BIT * sizeof(To) - 1)) - 1);
- return aFrom <= From(MaxValue);
- }
- };
- template<typename From, typename To>
- struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsSigned>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return UnsignedSignedCheck<From, To>::checkBounds(aFrom);
- }
- };
- // Signed-to-signed range check
- template<typename From, typename To>
- struct BoundsCheckImpl<From, To, FromIsSigned, ToIsSigned>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- if (sizeof(From) <= sizeof(To)) {
- return true;
- }
- const To MaxValue = To((1ULL << (CHAR_BIT * sizeof(To) - 1)) - 1);
- const To MinValue = -MaxValue - To(1);
- return From(MinValue) <= aFrom &&
- From(aFrom) <= From(MaxValue);
- }
- };
- template<typename From, typename To,
- bool TypesAreIntegral = IsIntegral<From>::value &&
- IsIntegral<To>::value>
- class BoundsChecker;
- template<typename From>
- class BoundsChecker<From, From, true>
- {
- public:
- static bool checkBounds(const From aFrom) { return true; }
- };
- template<typename From, typename To>
- class BoundsChecker<From, To, true>
- {
- public:
- static bool checkBounds(const From aFrom)
- {
- return BoundsCheckImpl<From, To>::checkBounds(aFrom);
- }
- };
- template<typename From, typename To>
- inline bool
- IsInBounds(const From aFrom)
- {
- return BoundsChecker<From, To>::checkBounds(aFrom);
- }
- } // namespace detail
- /**
- * Cast a value of integral type |From| to a value of integral type |To|,
- * asserting that the cast will be a safe cast per C++ (that is, that |to| is in
- * the range of values permitted for the type |From|).
- */
- template<typename To, typename From>
- inline To
- AssertedCast(const From aFrom)
- {
- MOZ_ASSERT((detail::IsInBounds<From, To>(aFrom)));
- return static_cast<To>(aFrom);
- }
- /**
- * Cast a value of integral type |From| to a value of integral type |To|,
- * release asserting that the cast will be a safe cast per C++ (that is, that
- * |to| is in the range of values permitted for the type |From|).
- */
- template<typename To, typename From>
- inline To
- ReleaseAssertedCast(const From aFrom)
- {
- MOZ_RELEASE_ASSERT((detail::IsInBounds<From, To>(aFrom)));
- return static_cast<To>(aFrom);
- }
- } // namespace mozilla
- #endif /* mozilla_Casting_h */
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