Revision: 24420
Author: [email protected]
Date: Mon Oct 6 15:23:59 2014 UTC
Log: Don't use identity as hash function for integers.
Also slightly improve hashing of floats/doubles.
TEST=unittests
[email protected]
Review URL: https://codereview.chromium.org/632713002
https://code.google.com/p/v8/source/detail?r=24420
Modified:
/branches/bleeding_edge/src/base/functional.cc
/branches/bleeding_edge/src/base/functional.h
/branches/bleeding_edge/test/unittests/base/functional-unittest.cc
=======================================
--- /branches/bleeding_edge/src/base/functional.cc Mon Oct 6 12:27:24 2014
UTC
+++ /branches/bleeding_edge/src/base/functional.cc Mon Oct 6 15:23:59 2014
UTC
@@ -62,6 +62,19 @@
#endif // V8_HOST_ARCH_32_BIT
return seed;
}
+
+
+// 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)
@@ -76,13 +89,13 @@
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
=======================================
--- /branches/bleeding_edge/src/base/functional.h Mon Oct 6 12:27:24 2014
UTC
+++ /branches/bleeding_edge/src/base/functional.h Mon Oct 6 15:23:59 2014
UTC
@@ -76,11 +76,11 @@
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) { \
=======================================
--- /branches/bleeding_edge/test/unittests/base/functional-unittest.cc Mon
Oct 6 12:27:24 2014 UTC
+++ /branches/bleeding_edge/test/unittests/base/functional-unittest.cc Mon
Oct 6 15:23:59 2014 UTC
@@ -83,7 +83,7 @@
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;
--
--
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