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https://github.com/encounter/dawn-cmake.git
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250f26229b
Bug: dawn:442 Change-Id: I889a943cbaf2d349c31a15fdf126d66964bdd0a7 Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/23247 Commit-Queue: Austin Eng <enga@chromium.org> Reviewed-by: Stephen White <senorblanco@chromium.org>
102 lines
3.5 KiB
C++
102 lines
3.5 KiB
C++
// Copyright 2018 The Dawn Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef COMMON_HASHUTILS_H_
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#define COMMON_HASHUTILS_H_
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#include "common/Platform.h"
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#include "common/TypedInteger.h"
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#include "common/ityp_bitset.h"
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#include <bitset>
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#include <functional>
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// Wrapper around std::hash to make it a templated function instead of a functor. It is marginally
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// nicer, and avoids adding to the std namespace to add hashing of other types.
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template <typename T>
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size_t Hash(const T& value) {
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return std::hash<T>()(value);
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}
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// Add hashing of TypedIntegers
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template <typename Tag, typename T>
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size_t Hash(const TypedInteger<Tag, T>& value) {
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return Hash(static_cast<T>(value));
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}
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// When hashing sparse structures we want to iteratively build a hash value with only parts of the
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// data. HashCombine "hashes" together an existing hash and hashable values.
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//
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// Example usage to compute the hash of a mask and values corresponding to the mask:
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//
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// size_t hash = Hash(mask):
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// for (uint32_t i : IterateBitSet(mask)) { HashCombine(&hash, hashables[i]); }
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// return hash;
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template <typename T>
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void HashCombine(size_t* hash, const T& value) {
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#if defined(DAWN_PLATFORM_64_BIT)
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const size_t offset = 0x9e3779b97f4a7c16;
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#elif defined(DAWN_PLATFORM_32_BIT)
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const size_t offset = 0x9e3779b9;
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#else
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# error "Unsupported platform"
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#endif
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*hash ^= Hash(value) + offset + (*hash << 6) + (*hash >> 2);
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}
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template <typename T, typename... Args>
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void HashCombine(size_t* hash, const T& value, const Args&... args) {
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HashCombine(hash, value);
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HashCombine(hash, args...);
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}
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// Workaround a bug between clang++ and libstdlibc++ by defining our own hashing for bitsets.
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// When _GLIBCXX_DEBUG is enabled libstdc++ wraps containers into debug containers. For bitset this
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// means what is normally std::bitset is defined as std::__cxx1988::bitset and is replaced by the
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// debug version of bitset.
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// When hashing, std::hash<std::bitset> proxies the call to std::hash<std::__cxx1998::bitset> and
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// fails on clang because the latter tries to access the private _M_getdata member of the bitset.
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// It looks like it should work because the non-debug bitset declares
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//
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// friend struct std::hash<bitset> // bitset is the name of the class itself
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//
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// which should friend std::hash<std::__cxx1998::bitset> but somehow doesn't work on clang.
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#if defined(_GLIBCXX_DEBUG)
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template <size_t N>
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size_t Hash(const std::bitset<N>& value) {
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constexpr size_t kWindowSize = sizeof(unsigned long long);
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std::bitset<N> bits = value;
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size_t hash = 0;
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for (size_t processedBits = 0; processedBits < N; processedBits += kWindowSize) {
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HashCombine(&hash, bits.to_ullong());
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bits >>= kWindowSize;
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}
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return hash;
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}
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#endif
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namespace std {
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template <typename Index, size_t N>
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class hash<ityp::bitset<Index, N>> {
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public:
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size_t operator()(const ityp::bitset<Index, N>& value) const {
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return Hash(static_cast<const std::bitset<N>&>(value));
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}
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};
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} // namespace std
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#endif // COMMON_HASHUTILS_H_
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