108 lines
3.3 KiB
C++
Executable File
108 lines
3.3 KiB
C++
Executable File
/*
|
|
* Copyright (C) 2022 The Android Open Source Project
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
|
|
#ifndef SkSafeMath_DEFINED
|
|
#define SkSafeMath_DEFINED
|
|
|
|
#include <cstddef>
|
|
#include <cstdint>
|
|
#include <limits>
|
|
|
|
// Copy of Skia's SafeMath API used to validate Mesh parameters to support
|
|
// deferred creation of SkMesh instances on RenderThread.
|
|
// SafeMath 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 SafeMath {
|
|
public:
|
|
SafeMath() = 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;
|
|
}
|
|
|
|
// These saturate to their results
|
|
static size_t Add(size_t x, size_t y) {
|
|
SafeMath tmp;
|
|
size_t sum = tmp.add(x, y);
|
|
return tmp.ok() ? sum : SIZE_MAX;
|
|
}
|
|
|
|
static size_t Mul(size_t x, size_t y) {
|
|
SafeMath tmp;
|
|
size_t prod = tmp.mul(x, y);
|
|
return tmp.ok() ? prod : SIZE_MAX;
|
|
}
|
|
|
|
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;
|
|
// Overflow information is capture in fOK. Return the result modulo 2^32.
|
|
return (uint32_t)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;
|
|
|
|
return result;
|
|
}
|
|
}
|
|
bool fOK = true;
|
|
};
|
|
|
|
#endif // SkSafeMath_DEFINED
|