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