/*
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* Copyright 2017 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkSafeMath_DEFINED
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#define SkSafeMath_DEFINED
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#include "SkTFitsIn.h"
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#include "SkTypes.h"
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#include <limits>
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// SkSafeMath always check that a series of operations do not overflow.
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// This must be correct for all platforms, because this is a check for safety at runtime.
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class SkSafeMath {
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public:
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SkSafeMath() = default;
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bool ok() const { return fOK; }
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explicit operator bool() const { return fOK; }
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size_t mul(size_t x, size_t y) {
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return sizeof(size_t) == sizeof(uint64_t) ? mul64(x, y) : mul32(x, y);
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}
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size_t add(size_t x, size_t y) {
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size_t result = x + y;
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fOK &= result >= x;
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return result;
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}
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/**
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* Return a + b, unless this result is an overflow/underflow. In those cases, fOK will
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* be set to false, and it is undefined what this returns.
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*/
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int addInt(int a, int b) {
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if (b < 0 && a < std::numeric_limits<int>::min() - b) {
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fOK = false;
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return a;
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} else if (b > 0 && a > std::numeric_limits<int>::max() - b) {
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fOK = false;
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return a;
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}
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return a + b;
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}
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size_t alignUp(size_t x, size_t alignment) {
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SkASSERT(alignment && !(alignment & (alignment - 1)));
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return add(x, alignment - 1) & ~(alignment - 1);
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}
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template <typename T> T castTo(size_t value) {
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if (!SkTFitsIn<T>(value)) {
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fOK = false;
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}
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return static_cast<T>(value);
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}
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// These saturate to their results
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static size_t Add(size_t x, size_t y);
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static size_t Mul(size_t x, size_t y);
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static size_t Align4(size_t x) {
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SkSafeMath safe;
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return safe.alignUp(x, 4);
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}
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private:
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uint32_t mul32(uint32_t x, uint32_t y) {
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uint64_t bx = x;
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uint64_t by = y;
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uint64_t result = bx * by;
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fOK &= result >> 32 == 0;
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return result;
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}
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uint64_t mul64(uint64_t x, uint64_t y) {
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if (x <= std::numeric_limits<uint64_t>::max() >> 32
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&& y <= std::numeric_limits<uint64_t>::max() >> 32) {
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return x * y;
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} else {
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auto hi = [](uint64_t x) { return x >> 32; };
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auto lo = [](uint64_t x) { return x & 0xFFFFFFFF; };
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uint64_t lx_ly = lo(x) * lo(y);
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uint64_t hx_ly = hi(x) * lo(y);
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uint64_t lx_hy = lo(x) * hi(y);
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uint64_t hx_hy = hi(x) * hi(y);
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uint64_t result = 0;
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result = this->add(lx_ly, (hx_ly << 32));
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result = this->add(result, (lx_hy << 32));
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fOK &= (hx_hy + (hx_ly >> 32) + (lx_hy >> 32)) == 0;
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#if defined(SK_DEBUG) && defined(__clang__) && defined(__x86_64__)
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auto double_check = (unsigned __int128)x * y;
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SkASSERT(result == (double_check & 0xFFFFFFFFFFFFFFFF));
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SkASSERT(!fOK || (double_check >> 64 == 0));
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#endif
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return result;
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}
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}
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bool fOK = true;
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};
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#endif//SkSafeMath_DEFINED
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