123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108 |
- /*
- * 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
|