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