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/*
* Copyright (c) 2012 Google Inc. All rights reserved.
* Copyright (C) 2014-2021 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <limits>
#include <stdint.h>
#include <stdlib.h>
#include <wtf/Compiler.h>
namespace WTF {
// FIXME: Enhance this so it fails to compile calls where either of the arguments can be outside the range of the integral type instead of quietly converting.
template<std::signed_integral SignedIntegralType>
SignedIntegralType saturatedSum(SignedIntegralType, SignedIntegralType);
template<std::unsigned_integral UnsignedIntegralType>
constexpr UnsignedIntegralType saturatedSum(UnsignedIntegralType, UnsignedIntegralType);
template<typename IntegralType>
IntegralType saturatedDifference(IntegralType, IntegralType);
inline bool signedAddInt32Overflows(int32_t a, int32_t b, int32_t& result)
{
#if COMPILER_HAS_CLANG_BUILTIN(__builtin_sadd_overflow) && !(defined __clang_major__ && __clang_major__ < 7)
return __builtin_sadd_overflow(a, b, &result);
#else
uint32_t ua = a;
uint32_t ub = b;
uint32_t uresult = ua + ub;
result = static_cast<int32_t>(uresult);
// Can only overflow if the signed bit of the two values match. If the signed
// bit of the result and one of the values differ it did overflow.
return !((ua ^ ub) >> 31) && (uresult ^ ua) >> 31;
#endif
}
template<> inline int32_t saturatedSum<int32_t>(int32_t a, int32_t b)
{
int32_t result;
#if CPU(ARM_THUMB2)
__asm__("qadd %[sum], %[addend], %[augend]"
: [sum]"=r"(result)
: [augend]"r"(a), [addend]"r"(b)
: /* Nothing is clobbered. */
);
#else
if (signedAddInt32Overflows(a, b, result))
result = std::numeric_limits<int32_t>::max() + (static_cast<uint32_t>(a) >> 31);
#endif
return result;
}
inline bool signedSubtractInt32Overflows(int32_t a, int32_t b, int32_t& result)
{
#if COMPILER_HAS_CLANG_BUILTIN(__builtin_ssub_overflow) && !(defined __clang_major__ && __clang_major__ < 7)
return __builtin_ssub_overflow(a, b, &result);
#else
uint32_t ua = a;
uint32_t ub = b;
uint32_t uresult = ua - ub;
result = static_cast<int32_t>(uresult);
// Can only overflow if the signed bit of the two values do not match. If the
// signed bit of the result and the first value differ it did overflow.
return (ua ^ ub) >> 31 && (uresult ^ ua) >> 31;
#endif
}
// FIXME: Enhance this so it fails to compile calls where either of the arguments can be outside the range of int32_t instead of quietly converting.
template<> inline int32_t saturatedDifference<int32_t>(int32_t a, int32_t b)
{
int32_t result;
#if CPU(ARM_THUMB2)
__asm__("qsub %[difference], %[minuend], %[subtrahend]"
: [difference]"=r"(result)
: [minuend]"r"(a), [subtrahend]"r"(b)
: /* Nothing is clobbered. */
);
#else
if (signedSubtractInt32Overflows(a, b, result))
result = std::numeric_limits<int32_t>::max() + (static_cast<uint32_t>(a) >> 31);
#endif
return result;
}
template<std::unsigned_integral UnsignedIntegralType>
constexpr UnsignedIntegralType saturatedSum(UnsignedIntegralType a, UnsignedIntegralType b)
{
auto sum = a + b;
return sum < a ? std::numeric_limits<UnsignedIntegralType>::max() : sum;
}
template<typename IntegralType, typename... ArgumentTypes>
constexpr uint32_t saturatedSum(IntegralType value, ArgumentTypes... arguments)
{
return saturatedSum<IntegralType>(value, saturatedSum<IntegralType>(arguments...));
}
}
using WTF::saturatedSum;
using WTF::saturatedDifference;
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