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Move HashCombine to HashUtils and make it work better on 64bits

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HashCombine will be used in more than just BindGroupLayout caching so we
extract it to a separate header. Add a better mixing constant for 64bit
systems.
This commit is contained in:
Corentin Wallez
2018-05-07 17:33:48 -04:00
committed by Corentin Wallez
parent 60ffbfc071
commit ae27c7a4bc
3 changed files with 58 additions and 22 deletions
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24
src/backend/BindGroupLayout.cpp
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@@ -15,39 +15,19 @@
#include "backend/BindGroupLayout.h"
#include "backend/Device.h"
#include "common/HashUtils.h"
#include <functional>
namespace backend {
namespace {
// Workaround for Chrome's stdlib having a broken std::hash for enums and bitsets
template <typename T>
typename std::enable_if<std::is_enum<T>::value, size_t>::type Hash(T value) {
using Integral = typename nxt::UnderlyingType<T>::type;
return std::hash<Integral>()(static_cast<Integral>(value));
}
template <size_t N>
size_t Hash(const std::bitset<N>& value) {
static_assert(N <= sizeof(unsigned long long) * 8, "");
return std::hash<unsigned long long>()(value.to_ullong());
}
// TODO(cwallez@chromium.org): see if we can use boost's hash combined or some equivalent
// this currently assumes that size_t is 64 bits
void CombineHashes(size_t* h1, size_t h2) {
*h1 ^= (h2 << 7) + (h2 >> (sizeof(size_t) * 8 - 7)) + 0x304975;
}
size_t HashBindingInfo(const BindGroupLayoutBase::LayoutBindingInfo& info) {
size_t hash = Hash(info.mask);
for (size_t binding = 0; binding < kMaxBindingsPerGroup; ++binding) {
if (info.mask[binding]) {
CombineHashes(&hash, Hash(info.visibilities[binding]));
CombineHashes(&hash, Hash(info.types[binding]));
HashCombine(&hash, info.visibilities[binding], info.types[binding]);
}
}