Changeset 36117 in webkit for trunk/JavaScriptCore/ChangeLog

Timestamp:

Sep 5, 2008, 2:51:22 PM (17 years ago)

Author:

Darin Adler

Message:

2008-09-05 Darin Adler <Darin Adler>

Reviewed by Sam Weinig.

• fix ​https://bugs.webkit.org/show_bug.cgi?id=20671 JavaScriptCore string manipulation spends too much time in memcpy

1.011x as fast on SunSpider overall
1.028x as fast on SunSpider string tests

For small strings, use a loop rather than calling memcpy. The loop can
be faster because there's no function call overhead, and because it can
assume the pointers are aligned instead of checking that. Currently the
threshold is set at 20 characters, based on some testing on one particular
computer. Later we can tune this for various platforms by setting
USTRING_COPY_CHARS_INLINE_CUTOFF appropriately, but it does no great harm
if not perfectly tuned.

• kjs/ustring.cpp: (KJS::overflowIndicator): Removed bogus const. (KJS::maxUChars): Ditto. (KJS::copyChars): Added. (KJS::UString::Rep::createCopying): Call copyChars instead of memcpy. Also eliminated need for const_cast. (KJS::UString::expandPreCapacity): Ditto. (KJS::concatenate): Ditto. (KJS::UString::spliceSubstringsWithSeparators): Ditto. (KJS::UString::append): Ditto.

File:

• trunk/JavaScriptCore/ChangeLog (modified) (1 diff)

trunk/JavaScriptCore/ChangeLog

@@ +1 @@
+2008-09-05  Darin Adler  <[email protected]>
+
+        Reviewed by Sam Weinig.
+
+        - fix https://bugs.webkit.org/show_bug.cgi?id=20671
+          JavaScriptCore string manipulation spends too much time in memcpy
+
+        1.011x as fast on SunSpider overall
+        1.028x as fast on SunSpider string tests
+
+        For small strings, use a loop rather than calling memcpy. The loop can
+        be faster because there's no function call overhead, and because it can
+        assume the pointers are aligned instead of checking that. Currently the
+        threshold is set at 20 characters, based on some testing on one particular
+        computer. Later we can tune this for various platforms by setting
+        USTRING_COPY_CHARS_INLINE_CUTOFF appropriately, but it does no great harm
+        if not perfectly tuned.
+
+        * kjs/ustring.cpp:
+        (KJS::overflowIndicator): Removed bogus const.
+        (KJS::maxUChars): Ditto.
+        (KJS::copyChars): Added.
+        (KJS::UString::Rep::createCopying): Call copyChars instead of memcpy.
+        Also eliminated need for const_cast.
+        (KJS::UString::expandPreCapacity): Ditto.
+        (KJS::concatenate): Ditto.
+        (KJS::UString::spliceSubstringsWithSeparators): Ditto.
+        (KJS::UString::append): Ditto.
+
 2008-09-05  Kevin McCullough  <[email protected]>