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/* -*- 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 {
/**
* Return a value of type |To|, containing the underlying bit pattern of |from|.
*
* |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.
*/
template<typename To, typename From>
inline To
BitwiseCast(const From from)
{
MOZ_STATIC_ASSERT(sizeof(From) == sizeof(To),
"To and From must have the same size");
union {
From from;
To to;
} u;
u.from = from;
return u.to;
}
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 from) {
return from <= From(To(-1));
}
};
template<typename From, typename To>
struct UnsignedUnsignedCheck<From, To, FromIsNotBigger>
{
public:
static bool checkBounds(const From from) {
return true;
}
};
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsUnsigned>
{
public:
static bool checkBounds(const From from) {
return UnsignedUnsignedCheck<From, To>::checkBounds(from);
}
};
// Signed-to-unsigned range check
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsSigned, ToIsUnsigned>
{
public:
static bool checkBounds(const From from) {
if (from < 0)
return false;
if (sizeof(To) >= sizeof(From))
return true;
return from <= 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 from) {
return true;
}
};
template<typename From, typename To>
struct UnsignedSignedCheck<From, To, FromIsNotSmaller>
{
public:
static bool checkBounds(const From from) {
const To MaxValue = To((1ULL << (CHAR_BIT * sizeof(To) - 1)) - 1);
return from <= From(MaxValue);
}
};
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsUnsigned, ToIsSigned>
{
public:
static bool checkBounds(const From from) {
return UnsignedSignedCheck<From, To>::checkBounds(from);
}
};
// Signed-to-signed range check
template<typename From, typename To>
struct BoundsCheckImpl<From, To, FromIsSigned, ToIsSigned>
{
public:
static bool checkBounds(const From from) {
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) <= from &&
From(from) <= 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 from) { return true; }
};
template<typename From, typename To>
class BoundsChecker<From, To, true>
{
public:
static bool checkBounds(const From from) {
return BoundsCheckImpl<From, To>::checkBounds(from);
}
};
template<typename From, typename To>
inline bool
IsInBounds(const From from)
{
return BoundsChecker<From, To>::checkBounds(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_ */
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