js-crc32/bits/40_crc.js
SheetJS c79a8fb6c9 version bump 0.2.0: performance
- used Int32Array for storing CRC32 table when possible
- buf/array impl 4-step unrolling
- integration performance tests
2014-06-17 19:20:41 -04:00

53 lines
1.9 KiB
JavaScript

/* charCodeAt is the best approach for binary strings */
var use_buffer = typeof Buffer !== 'undefined';
function crc32_bstr(bstr) {
if(bstr.length > 32768) if(use_buffer) return crc32_buf(Buffer(bstr));
var crc = -1, L = bstr.length - 1;
for(var i = 0; i < L;) {
crc = table[(crc ^ bstr.charCodeAt(i++)) & 0xFF] ^ (crc >>> 8);
crc = table[(crc ^ bstr.charCodeAt(i++)) & 0xFF] ^ (crc >>> 8);
}
if(i === L) crc = (crc >>> 8) ^ table[(crc ^ bstr.charCodeAt(i)) & 0xFF];
return crc ^ -1;
}
function crc32_buf(buf) {
for(var crc = -1, i = 0, L=buf.length-3; i < L;) {
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
}
if(i < L+3) {
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
if(i < L+3) {
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF];
if(i < L+3) {
crc = (crc >>> 8) ^ table[(crc^buf[i++])&0xFF]; }}}
return crc ^ -1;
}
/* much much faster to intertwine utf8 and crc */
function crc32_str(str) {
for(var crc = -1, i = 0, L=str.length, c, d; i < L;) {
c = str.charCodeAt(i++);
if(c < 0x80) {
crc = (crc >>> 8) ^ table[(crc ^ c) & 0xFF];
} else if(c < 0x800) {
crc = (crc >>> 8) ^ table[(crc ^ (192|((c>>6)&31))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|(c&63))) & 0xFF];
} else if(c >= 0xD800 && c < 0xE000) {
c = (c&1023)+64; d = str.charCodeAt(i++) & 1023;
crc = (crc >>> 8) ^ table[(crc ^ (240|((c>>8)&7))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|((c>>2)&63))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|((d>>6)&15)|(c&3))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|(d&63))) & 0xFF];
} else {
crc = (crc >>> 8) ^ table[(crc ^ (224|((c>>12)&15))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|((c>>6)&63))) & 0xFF];
crc = (crc >>> 8) ^ table[(crc ^ (128|(c&63))) & 0xFF];
}
}
return crc ^ -1;
}