Author: l...@chromium.org
Date: Wed May 6 01:42:36 2009
New Revision: 1876
Modified:
branches/bleeding_edge/src/stub-cache.h
Log:
X64: Changed hash computations to only use lower 32 bits of pointers.
Review URL: http://codereview.chromium.org/115017
Modified: branches/bleeding_edge/src/stub-cache.h
==============================================================================
--- branches/bleeding_edge/src/stub-cache.h (original)
+++ branches/bleeding_edge/src/stub-cache.h Wed May 6 01:42:36 2009
@@ -203,14 +203,21 @@
// Compute the hash of the name (use entire length field).
ASSERT(name->HasHashCode());
uint32_t field = name->length_field();
+ // Using only the low bits in 64-bit mode is unlikely to increase the
+ // risk of collision even if the heap is spread over an area larger
than
+ // 4Gb (and not at all if it isn't).
+ uint32_t map_low32bits =
+ static_cast<uint32_t>(reinterpret_cast<uintptr_t>(map));
// Base the offset on a simple combination of name, flags, and map.
- uint32_t key = (reinterpret_cast<uint32_t>(map) + field) ^ flags;
+ uint32_t key = (map_low32bits + field) ^ flags;
return key & ((kPrimaryTableSize - 1) << kHeapObjectTagSize);
}
static int SecondaryOffset(String* name, Code::Flags flags, int seed) {
// Use the seed from the primary cache in the secondary cache.
- uint32_t key = seed - reinterpret_cast<uint32_t>(name) + flags;
+ uint32_t string_low32bits =
+ static_cast<uint32_t>(reinterpret_cast<uintptr_t>(name));
+ uint32_t key = seed - string_low32bits + flags;
return key & ((kSecondaryTableSize - 1) << kHeapObjectTagSize);
}
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