js-adler32/bits/40_adler.js

61 lines
1.6 KiB
JavaScript
Raw Permalink Normal View History

2014-06-18 17:58:20 +00:00
/* consult README.md for the magic number */
/* charCodeAt is the best approach for binary strings */
var use_buffer = typeof Buffer !== 'undefined';
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, 3850)+i;
for(;i<M;i++) {
a += bstr.charCodeAt(i);
2014-06-18 17:58:20 +00:00
b += a;
}
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
2014-06-18 17:58:20 +00:00
}
return ((b%65521) << 16) | (a%65521);
2014-06-18 17:58:20 +00:00
}
function adler32_buf(buf) {
var a = 1, b = 0, L = buf.length, M;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3850)+i;
for(;i<M;i++) {
a += buf[i];
2014-06-18 17:58:20 +00:00
b += a;
}
a = (15*(a>>>16)+(a&65535))
b = (15*(b>>>16)+(b&65535))
2014-06-18 17:58:20 +00:00
}
return ((b%65521) << 16) | (a%65521);
2014-06-18 17:58:20 +00:00
}
/* much much faster to intertwine utf8 and adler */
function adler32_str(str) {
var a = 1, b = 0, L = str.length, M, c, d;
for(var i = 0; i < L;) {
M = Math.min(L-i, 3850);
while(M>0) {
c = str.charCodeAt(i++);
if(c < 0x80) { a += c; b += a; --M; }
else if(c < 0x800) {
a += 192|((c>>6)&31); b += a; --M;
a += 128|(c&63); b += a; --M;
} else if(c >= 0xD800 && c < 0xE000) {
c = (c&1023)+64; d = str.charCodeAt(i++) & 1023;
a += 240|((c>>8)&7); b += a; --M;
a += 128|((c>>2)&63); b += a; --M;
a += 128|((d>>6)&15)|(c&3); b += a; --M;
a += 128|(d&63); b += a; --M;
} else {
a += 224|((c>>12)&15); b += a; --M;
a += 128|((c>>6)&63); b += a; --M;
a += 128|(c&63); b += a; --M;
}
}
a %= 65521;
b %= 65521;
}
return (b << 16) | a;
2014-06-18 17:58:20 +00:00
}