From c074b18f8d4510713f6d66149213510428eae6f1 Mon Sep 17 00:00:00 2001
From: Christian Kamm <christian.d.kamm@nokia.com>
Date: Wed, 7 Sep 2011 08:45:01 +0200
Subject: [PATCH] C++: Improve Literal::hashCode.
This can have a dramatic impact on performance when a file contains lots
of unique literals.
Change-Id: I5309b28f704d7f53e164dc8084ae08354c09354b
Reviewed-on: http://codereview.qt.nokia.com/4312
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>
---
src/libs/3rdparty/cplusplus/Literals.cpp | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/src/libs/3rdparty/cplusplus/Literals.cpp b/src/libs/3rdparty/cplusplus/Literals.cpp
index 16eab541d7b..d0aa05d3512 100644
--- a/src/libs/3rdparty/cplusplus/Literals.cpp
+++ b/src/libs/3rdparty/cplusplus/Literals.cpp
@@ -75,9 +75,21 @@ unsigned Literal::hashCode() const
unsigned Literal::hashCode(const char *chars, unsigned size)
{
- unsigned h = 0;
- for (unsigned i = 0; i < size; ++i)
- h = (h >> 5) - h + chars[i];
+ /* Hash taken from QtCore's qHash for strings, which in turn has the note:
+
+ These functions are based on Peter J. Weinberger's hash function
+ (from the Dragon Book). The constant 24 in the original function
+ was replaced with 23 to produce fewer collisions on input such as
+ "a", "aa", "aaa", "aaaa", ...
+ */
+
+ uint h = 0;
+
+ while (size--) {
+ h = (h << 4) + *chars++;
+ h ^= (h & 0xf0000000) >> 23;
+ h &= 0x0fffffff;
+ }
return h;
}
--
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