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String search performance improvements:

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* Using memchr for first/only char lookup is faster than hand-coded
   loop. It processes one machine word per iteration so it helps even
   more on x64.

 * Tweaked badness computation in simple search. We pay only for the
   first char memchr scans, not for all of them.

Review URL: http://codereview.chromium.org/1100002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4173 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
vitalyr@chromium.org 2010-03-18 09:01:08 +00:00
parent e090f46a55
commit b148282b56
1 changed files with 29 additions and 2 deletions
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27
src/runtime.cc
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@ -2353,6 +2353,14 @@ template <typename schar>
static inline int SingleCharIndexOf(Vector<const schar> string,
schar pattern_char,
int start_index) {
if (sizeof(schar) == 1) {
schar* pos = reinterpret_cast<schar*>(
memchr(string.start() + start_index,
pattern_char,
string.length() - start_index));
if (pos == NULL) return -1;
return pos - string.start();
}
for (int i = start_index, n = string.length(); i < n; i++) {
if (pattern_char == string[i]) {
return i;
@ -2400,7 +2408,18 @@ static int SimpleIndexOf(Vector<const schar> subject,
*complete = false;
return i;
}
if (sizeof(schar) == 1 && sizeof(pchar) == 1) {
schar* pos = reinterpret_cast<schar*>(memchr(subject.start() + i,
pattern_first_char,
n - i + 1));
if (pos == NULL) {
*complete = true;
return -1;
}
i = pos - subject.start();
} else {
if (subject[i] != pattern_first_char) continue;
}
int j = 1;
do {
if (pattern[j] != subject[i+j]) {
@ -2425,7 +2444,15 @@ static int SimpleIndexOf(Vector<const schar> subject,
int idx) {
pchar pattern_first_char = pattern[0];
for (int i = idx, n = subject.length() - pattern.length(); i <= n; i++) {
if (sizeof(schar) == 1 && sizeof(pchar) == 1) {
schar* pos = reinterpret_cast<schar*>(memchr(subject.start() + i,
pattern_first_char,
n - i + 1));
if (pos == NULL) return -1;
i = pos - subject.start();
} else {
if (subject[i] != pattern_first_char) continue;
}
int j = 1;
do {
if (pattern[j] != subject[i+j]) {