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buffer: optimize Buffer#toString()
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Break up Buffer#toString() into a fast and slow path.  The fast path
optimizes for zero-length buffers and no-arg method invocation.

The speedup for zero-length buffers is a satisfying 700%.  The no-arg
toString() operation gets faster by about 13% for a one-byte buffer.

This change exploits the fact that most Buffer#toString() calls are
plain no-arg method calls.  Rewriting the method to take no arguments
means a call doesn't go through an ArgumentsAdaptorTrampoline stack
frame in the common case.

PR-URL: #2027
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Christian Tellnes <christian@tellnes.no>
Reviewed-By: Daniel Cousens <email@dcousens.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
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bnoordhuis committed Jun 25, 2015
1 parent 06721fe commit 8350f3a
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Showing 2 changed files with 37 additions and 2 deletions.
26 changes: 26 additions & 0 deletions benchmark/buffers/buffer-tostring.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
'use strict';

const common = require('../common.js');

const bench = common.createBenchmark(main, {
arg: [true, false],
len: [0, 1, 64, 1024],
n: [1e7]
});

function main(conf) {
const arg = conf.arg;
const len = conf.len | 0;
const n = conf.n | 0;
const buf = Buffer(len).fill(42);

bench.start();
if (arg) {
for (var i = 0; i < n; i += 1)
buf.toString('utf8');
} else {
for (var i = 0; i < n; i += 1)
buf.toString();
}
bench.end(n);
}
13 changes: 11 additions & 2 deletions lib/buffer.js
Original file line number Diff line number Diff line change
Expand Up @@ -333,8 +333,7 @@ function byteLength(string, encoding) {

Buffer.byteLength = byteLength;

// toString(encoding, start=0, end=buffer.length)
Buffer.prototype.toString = function(encoding, start, end) {
function slowToString(encoding, start, end) {
var loweredCase = false;

start = start >>> 0;
Expand Down Expand Up @@ -376,6 +375,16 @@ Buffer.prototype.toString = function(encoding, start, end) {
loweredCase = true;
}
}
}


Buffer.prototype.toString = function() {
const length = this.length | 0;
if (length === 0)
return '';
if (arguments.length === 0)
return this.utf8Slice(0, length);
return slowToString.apply(this, arguments);
};


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