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js-adler32
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version bump 0.2.0: safari performance 

On Safari, bit twiddling is 50% faster than directly evaluating mod 65521
This commit is contained in:
SheetJS 2014-06-19 23:53:37 -04:00
parent b53334db84
commit d0e9ff9b3d
6 changed files with 88 additions and 51 deletions
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11
README.md
View File

@ -51,6 +51,17 @@ decisions in the code).
[js-crc](http://git.io/crc32) has more performance notes
Bit twiddling is much faster than taking the mod on Safari and older Firefoxes.
Instead of taking the literal mod 65521, it is faster to keep it in the integers
by bit-shifting: `65536 ~ 15 mod 65521` so for nonnegative integer `a`:
```
a = (a >>> 16) * 65536 + (a & 65535) [equality]
a ~ (a >>> 16) * 15 + (a & 65535) mod 65521
```
The mod is taken at the very end, since the intermediate result may exceed 65521
## Magic Number
The magic numbers were chosen so as to not overflow a 31-bit integer:

26
adler32.js
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@ -10,29 +10,29 @@ function adler32_bstr(bstr) {
if(bstr.length > 32768) if(use_buffer) return adler32_buf(Buffer(bstr));
var a = 1, b = 0, L = bstr.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += bstr.charCodeAt(i++);
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += bstr.charCodeAt(i);
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
function adler32_buf(buf) {
var a = 1, b = 0, L = buf.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += buf[i++];
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += buf[i];
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
/* much much faster to intertwine utf8 and adler */
@ -61,7 +61,7 @@ function adler32_str(str) {
a %= 65521;
b %= 65521;
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return (b << 16) | a;
}
ADLER32.bstr = adler32_bstr;
ADLER32.buf = adler32_buf;

26
bits/40_adler.js
View File

@ -5,29 +5,29 @@ function adler32_bstr(bstr) {
if(bstr.length > 32768) if(use_buffer) return adler32_buf(Buffer(bstr));
var a = 1, b = 0, L = bstr.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += bstr.charCodeAt(i++);
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += bstr.charCodeAt(i);
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
function adler32_buf(buf) {
var a = 1, b = 0, L = buf.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += buf[i++];
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += buf[i];
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
/* much much faster to intertwine utf8 and adler */
@ -56,5 +56,5 @@ function adler32_str(str) {
a %= 65521;
b %= 65521;
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return (b << 16) | a;
}

26
ctest/adler32.js
View File

@ -10,29 +10,29 @@ function adler32_bstr(bstr) {
if(bstr.length > 32768) if(use_buffer) return adler32_buf(Buffer(bstr));
var a = 1, b = 0, L = bstr.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += bstr.charCodeAt(i++);
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += bstr.charCodeAt(i);
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
function adler32_buf(buf) {
var a = 1, b = 0, L = buf.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
for(;M>0;--M) {
a += buf[i++];
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += buf[i];
b += a;
}
a %= 65521;
b %= 65521;
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return ((b%65521) << 16) | (a%65521);
}
/* much much faster to intertwine utf8 and adler */
@ -61,7 +61,7 @@ function adler32_str(str) {
a %= 65521;
b %= 65521;
}
return b > 32767 ? (((b - 65536) * 65536) | a) : ((b * 65536) | a);
return (b << 16) | a;
}
ADLER32.bstr = adler32_bstr;
ADLER32.buf = adler32_buf;

2
package.json
View File

@ -1,6 +1,6 @@
{
"name": "adler-32",
"version": "0.1.0",
"version": "0.2.0",
"author": "sheetjs",
"description": "Pure-JS ADLER-32",
"keywords": [ "adler32", "checksum" ],

48
perf/bstr.js
View File

@ -1,5 +1,3 @@
var table = require('../').table;
function sheetjs1(bstr) {
var a = 1, b = 0, L = bstr.length;
for(var i = 0; i < L;) {
@ -14,7 +12,21 @@ function sheetjs1(bstr) {
function sheetjs2(bstr) {
var a = 1, b = 0, L = bstr.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3854);
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += bstr.charCodeAt(i);
b += a;
}
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
}
return ((b%65521) << 16) | (a%65521);
}
function sheetjs3(bstr) {
var a = 1, b = 0, L = bstr.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 5552);
for(;M>0;--M) {
a += bstr.charCodeAt(i++);
b += a;
@ -25,14 +37,28 @@ function sheetjs2(bstr) {
return (b << 16) | a;
}
var foobar = "foobarbazqux";
for(var i = 0; i != 11; ++i) foobar += " " + foobar;
var foobar = [255,255,255,255,255,255].map(function(x) { return String.fromCharCode(x); }).join("");
foobar += foobar;
foobar += foobar;
foobar += foobar;
foobar += foobar;
foobar += foobar;
foobar += foobar;
foobar.charCodeAt(0);
var m = 2048;
var assert = require('assert');
assert.equal(sheetjs1(foobar), sheetjs2(foobar));
var BM = require('./bm');
var suite = new BM('binary string');
for(var i = 0; i != 14; ++i) {
foobar += foobar;
foobar.charCodeAt(0);
assert.equal(sheetjs1(foobar), sheetjs3(foobar));
assert.equal(sheetjs1(foobar), sheetjs2(foobar));
//for(var j = 0; j != 200; ++j) assert.equal(sheetjs2(foobar), sheetjs3(foobar));
var suite = new BM('binary string (' + foobar.length + ')');
suite.add('sheetjs 1', function() { for(var j = 0; j != 1000; ++j) sheetjs1(foobar); });
suite.add('sheetjs 2', function() { for(var j = 0; j != 1000; ++j) sheetjs2(foobar); });
suite.run();
if(i<3) suite.add('sheetjs 1', function() { for(var j = 0; j != m; ++j) sheetjs1(foobar); });
suite.add('sheetjs 2', function() { for(var j = 0; j != m; ++j) sheetjs2(foobar); });
suite.add('sheetjs 3', function() { for(var j = 0; j != m; ++j) sheetjs3(foobar); });
suite.run();
m>>>=1; if(m < 10) m = 10;
}