adler32.js
1.62 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
'use strict';
// Note: adler32 takes 12% for level 0 and 2% for level 6.
// It isn't worth it to make additional optimizations as in original.
// Small size is preferable.
// (C) 1995-2013 Jean-loup Gailly and Mark Adler
// (C) 2014-2017 Vitaly Puzrin and Andrey Tupitsin
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
// claim that you wrote the original software. If you use this software
// in a product, an acknowledgment in the product documentation would be
// appreciated but is not required.
// 2. Altered source versions must be plainly marked as such, and must not be
// misrepresented as being the original software.
// 3. This notice may not be removed or altered from any source distribution.
function adler32(adler, buf, len, pos) {
var s1 = (adler & 0xffff) |0,
s2 = ((adler >>> 16) & 0xffff) |0,
n = 0;
while (len !== 0) {
// Set limit ~ twice less than 5552, to keep
// s2 in 31-bits, because we force signed ints.
// in other case %= will fail.
n = len > 2000 ? 2000 : len;
len -= n;
do {
s1 = (s1 + buf[pos++]) |0;
s2 = (s2 + s1) |0;
} while (--n);
s1 %= 65521;
s2 %= 65521;
}
return (s1 | (s2 << 16)) |0;
}
module.exports = adler32;