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Bug 865036 - Add a Casting.h header to hold various casting methods, right now including a SafeCast method that asserts in-rangeness. r=froydnj

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--HG--
extra : rebase_source : ef175e4c89d07cddbe866a40fc2ca521fa32c441
This commit is contained in:
Jeff Walden 2013-04-23 14:36:51 -07:00
parent 7c75754cf9
commit f685a81f44
4 changed files with 210 additions and 0 deletions
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128
mfbt/Casting.h Normal file
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@ -0,0 +1,128 @@
/* -*- Mode: C++; tab-width: 2; 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 {
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.
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsUnsigned>
{
public:
static bool check(const From from) {
typedef typename Conditional<sizeof(From) >= sizeof(To), From, To>::Type
LargerType;
return LargerType(from) <= LargerType(To(-1));
}
};
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsSigned, ToIsUnsigned>
{
public:
static bool check(const From from) {
if (from < 0)
return false;
if (sizeof(To) >= sizeof(From))
return To(from) <= To(-1);
return from <= From(To(-1));
}
};
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsSigned>
{
public:
static bool check(const From from) {
if (sizeof(From) < sizeof(To))
return true;
const To MaxValue = To((1ULL << (CHAR_BIT * sizeof(To) - 1)) - 1);
return from <= From(MaxValue);
}
};
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsSigned, ToIsSigned>
{
public:
static bool check(const From from) {
typedef typename Conditional<sizeof(To) >= sizeof(From), To, From>::Type
LargerType;
const To MaxValue = To((1ULL << (CHAR_BIT * sizeof(To) - 1)) - 1);
const To MinValue = -MaxValue - To(1);
return LargerType(MinValue) <= LargerType(from) &&
LargerType(from) <= LargerType(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 check(const From from) { return true; }
};
template<typename From, typename To>
class BoundsChecker<From, To, true>
{
public:
static bool check(const From from) {
return BoundsCheckImpl<From, To>::check(from);
}
};
template<typename From, typename To>
inline bool
IsInBounds(const From from)
{
return BoundsChecker<From, To>::check(from);
}
} // 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
SafeCast(const From from)
{
MOZ_ASSERT((detail::IsInBounds<From, To>(from)));
return static_cast<To>(from);
}
} // namespace mozilla
#endif /* mozilla_Casting_h_ */

1
mfbt/exported_headers.mk
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@ -12,6 +12,7 @@ EXPORTS_mozilla += \
Assertions.h \
Attributes.h \
BloomFilter.h \
Casting.h \
Char16.h \
CheckedInt.h \
Compiler.h \

1
mfbt/tests/Makefile.in
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@ -13,6 +13,7 @@ STL_FLAGS =
CPP_UNIT_TESTS = \
TestBloomFilter.cpp \
TestCasting.cpp \
TestCheckedInt.cpp \
TestEndian.cpp \
TestEnumSet.cpp \

80
mfbt/tests/TestCasting.cpp Normal file
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@ -0,0 +1,80 @@
/* -*- Mode: C++; tab-width: 2; 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/. */
#include "mozilla/Casting.h"
#include "mozilla/StandardInteger.h"
using mozilla::detail::IsInBounds;
static void
TestSameSize()
{
MOZ_ASSERT((IsInBounds<int16_t, int16_t>(int16_t(0))));
MOZ_ASSERT((IsInBounds<int16_t, int16_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((IsInBounds<int16_t, int16_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((IsInBounds<uint16_t, uint16_t>(uint16_t(UINT16_MAX))));
MOZ_ASSERT((IsInBounds<uint16_t, int16_t>(uint16_t(0))));
MOZ_ASSERT((!IsInBounds<uint16_t, int16_t>(uint16_t(-1))));
MOZ_ASSERT((!IsInBounds<int16_t, uint16_t>(int16_t(-1))));
MOZ_ASSERT((IsInBounds<int16_t, uint16_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((!IsInBounds<int16_t, uint16_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((IsInBounds<int32_t, uint32_t>(int32_t(INT32_MAX))));
MOZ_ASSERT((!IsInBounds<int32_t, uint32_t>(int32_t(INT32_MIN))));
}
static void
TestToBiggerSize()
{
MOZ_ASSERT((IsInBounds<int16_t, int32_t>(int16_t(0))));
MOZ_ASSERT((IsInBounds<int16_t, int32_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((IsInBounds<int16_t, int32_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((IsInBounds<uint16_t, uint32_t>(uint16_t(UINT16_MAX))));
MOZ_ASSERT((IsInBounds<uint16_t, int32_t>(uint16_t(0))));
MOZ_ASSERT((IsInBounds<uint16_t, int32_t>(uint16_t(-1))));
MOZ_ASSERT((!IsInBounds<int16_t, uint32_t>(int16_t(-1))));
MOZ_ASSERT((IsInBounds<int16_t, uint32_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((!IsInBounds<int16_t, uint32_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((IsInBounds<int32_t, uint64_t>(int32_t(INT32_MAX))));
MOZ_ASSERT((!IsInBounds<int32_t, uint64_t>(int32_t(INT32_MIN))));
}
static void
TestToSmallerSize()
{
MOZ_ASSERT((IsInBounds<int16_t, int8_t>(int16_t(0))));
MOZ_ASSERT((!IsInBounds<int16_t, int8_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((!IsInBounds<int16_t, int8_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((!IsInBounds<uint16_t, uint8_t>(uint16_t(UINT16_MAX))));
MOZ_ASSERT((IsInBounds<uint16_t, int8_t>(uint16_t(0))));
MOZ_ASSERT((!IsInBounds<uint16_t, int8_t>(uint16_t(-1))));
MOZ_ASSERT((!IsInBounds<int16_t, uint8_t>(int16_t(-1))));
MOZ_ASSERT((!IsInBounds<int16_t, uint8_t>(int16_t(INT16_MAX))));
MOZ_ASSERT((!IsInBounds<int16_t, uint8_t>(int16_t(INT16_MIN))));
MOZ_ASSERT((!IsInBounds<int32_t, uint16_t>(int32_t(INT32_MAX))));
MOZ_ASSERT((!IsInBounds<int32_t, uint16_t>(int32_t(INT32_MIN))));
// Boundary cases
MOZ_ASSERT((!IsInBounds<int64_t, int32_t>(int64_t(INT32_MIN) - 1)));
MOZ_ASSERT((IsInBounds<int64_t, int32_t>(int64_t(INT32_MIN))));
MOZ_ASSERT((IsInBounds<int64_t, int32_t>(int64_t(INT32_MIN) + 1)));
MOZ_ASSERT((IsInBounds<int64_t, int32_t>(int64_t(INT32_MAX) - 1)));
MOZ_ASSERT((IsInBounds<int64_t, int32_t>(int64_t(INT32_MAX))));
MOZ_ASSERT((!IsInBounds<int64_t, int32_t>(int64_t(INT32_MAX) + 1)));
MOZ_ASSERT((!IsInBounds<int64_t, uint32_t>(int64_t(-1))));
MOZ_ASSERT((IsInBounds<int64_t, uint32_t>(int64_t(0))));
MOZ_ASSERT((IsInBounds<int64_t, uint32_t>(int64_t(1))));
MOZ_ASSERT((IsInBounds<int64_t, uint32_t>(int64_t(UINT32_MAX) - 1)));
MOZ_ASSERT((IsInBounds<int64_t, uint32_t>(int64_t(UINT32_MAX))));
MOZ_ASSERT((!IsInBounds<int64_t, uint32_t>(int64_t(UINT32_MAX) + 1)));
}
int
main()
{
TestSameSize();
TestToBiggerSize();
TestToSmallerSize();
}