Reviewers: Dan Ehrenberg,
Description:
[es6] Use SubString in String{Starts,Ends}With
Much faster and constant than always searching the whole string
````
var allCodePoints = [];
for (var i = 0; i < 65536; i++) allCodePoints[i] = i;
var allCharsString = String.fromCharCode.apply(String, allCodePoints);
function bench(search) {
var counter = 0;
print(search + " found at " + allCharsString.startsWith(search));
var start = Date.now();
while (counter++ < 5000000) {
allCharsString.startsWith(search);
}
var end = Date.now();
print(end - start);
return counter;
}
print("single character");
bench("\u0000");
bench("\u0050");
bench("\u1000");
````
OLD
single character
found at true
374
P found at false
559
က found at false
13492
NEW
single character
found at true
261
P found at false
146
က found at false
146
BUG=
Please review this at https://codereview.chromium.org/1321853006/
Base URL: https://chromium.googlesource.com/v8/v8.git@master
Affected files (+2, -2 lines):
M src/string.js
Index: src/string.js
diff --git a/src/string.js b/src/string.js
index
1bbc8a69ce1259515bb950d2b259c5269056435a..1db65bb0bad25b677c7fa38144976c6a39f4ca18
100644
--- a/src/string.js
+++ b/src/string.js
@@ -997,7 +997,7 @@ function StringStartsWith(searchString /* position */)
{ // length == 1
return false;
}
- return %StringIndexOf(s, ss, start) === start;
+ return %_SubString(s, start, start + ss_len) === ss;
}
@@ -1028,7 +1028,7 @@ function StringEndsWith(searchString /* position */)
{ // length == 1
return false;
}
- return %StringLastIndexOf(s, ss, start) === start;
+ return %_SubString(s, start, start + ss_len) === ss;
}
--
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