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Don't use identity as hash function for integers.

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Also slightly improve hashing of floats/doubles.

TEST=unittests
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/632713002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24420 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
bmeurer@chromium.org 2014-10-06 15:23:59 +00:00
parent 711218bc07
commit 03255440de
3 changed files with 19 additions and 6 deletions
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17
src/base/functional.cc
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@ -64,6 +64,19 @@ size_t hash_combine(size_t seed, size_t value) {
}
// Thomas Wang, Integer Hash Functions.
// http://www.concentric.net/~Ttwang/tech/inthash.htm
size_t hash_value(unsigned int v) {
v = ~v + (v << 15); // v = (v << 15) - v - 1;
v = v ^ (v >> 12);
v = v + (v << 2);
v = v ^ (v >> 4);
v = v * 2057; // v = (v + (v << 3)) + (v << 11);
v = v ^ (v >> 16);
return v;
}
size_t hash_value(unsigned long v) { // NOLINT(runtime/int)
return hash_value_unsigned(v);
}
@ -76,13 +89,13 @@ size_t hash_value(unsigned long long v) { // NOLINT(runtime/int)
size_t hash_value(float v) {
// 0 and -0 both hash to zero.
return v != 0.0f ? hash_value(bit_cast<uint32_t>(v)) : 0;
return v != 0.0f ? hash_value_unsigned(bit_cast<uint32_t>(v)) : 0;
}
size_t hash_value(double v) {
// 0 and -0 both hash to zero.
return v != 0.0 ? hash_value(bit_cast<uint64_t>(v)) : 0;
return v != 0.0 ? hash_value_unsigned(bit_cast<uint64_t>(v)) : 0;
}
} // namespace base

6
src/base/functional.h
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@ -76,11 +76,11 @@ inline size_t hash_combine(T const& v, Ts const&... vs) {
V8_BASE_HASH_VALUE_TRIVIAL(bool)
V8_BASE_HASH_VALUE_TRIVIAL(unsigned char)
V8_BASE_HASH_VALUE_TRIVIAL(unsigned short) // NOLINT(runtime/int)
V8_BASE_HASH_VALUE_TRIVIAL(unsigned int)
#undef V8_BASE_HASH_VALUE_TRIVIAL
size_t hash_value(unsigned long v); // NOLINT(runtime/int)
size_t hash_value(unsigned long long v); // NOLINT(runtime/int)
size_t hash_value(unsigned int);
size_t hash_value(unsigned long); // NOLINT(runtime/int)
size_t hash_value(unsigned long long); // NOLINT(runtime/int)
#define V8_BASE_HASH_VALUE_SIGNED(type) \
inline size_t hash_value(signed type v) { \

2
test/unittests/base/functional-unittest.cc
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@ -83,7 +83,7 @@ TYPED_TEST(FunctionalTest, HashIsStateless) {
TYPED_TEST(FunctionalTest, HashIsOkish) {
const size_t kValues = 128;
const size_t kMinHashes = kValues / (sizeof(uint64_t) / sizeof(size_t));
const size_t kMinHashes = kValues / 4;
std::set<TypeParam> vs;
while (vs.size() != kValues) {
TypeParam v;