You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
102 lines
2.1 KiB
102 lines
2.1 KiB
3 years ago
|
(function () {
|
||
|
|
'use strict';
|
||
|
|
|
||
|
|
var table = [],
|
||
|
|
poly = 0xEDB88320; // reverse polynomial
|
||
|
|
|
||
|
|
// build the table
|
||
|
|
function makeTable() {
|
||
|
|
var c, n, k;
|
||
|
|
|
||
|
|
for (n = 0; n < 256; n += 1) {
|
||
|
|
c = n;
|
||
|
|
for (k = 0; k < 8; k += 1) {
|
||
|
|
if (c & 1) {
|
||
|
|
c = poly ^ (c >>> 1);
|
||
|
|
} else {
|
||
|
|
c = c >>> 1;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
table[n] = c >>> 0;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
function strToArr(str) {
|
||
|
|
// sweet hack to turn string into a 'byte' array
|
||
|
|
return Array.prototype.map.call(str, function (c) {
|
||
|
|
return c.charCodeAt(0);
|
||
|
|
});
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Compute CRC of array directly.
|
||
|
|
*
|
||
|
|
* This is slower for repeated calls, so append mode is not supported.
|
||
|
|
*/
|
||
|
|
function crcDirect(arr) {
|
||
|
|
var crc = -1, // initial contents of LFBSR
|
||
|
|
i, j, l, temp;
|
||
|
|
|
||
|
|
for (i = 0, l = arr.length; i < l; i += 1) {
|
||
|
|
temp = (crc ^ arr[i]) & 0xff;
|
||
|
|
|
||
|
|
// read 8 bits one at a time
|
||
|
|
for (j = 0; j < 8; j += 1) {
|
||
|
|
if ((temp & 1) === 1) {
|
||
|
|
temp = (temp >>> 1) ^ poly;
|
||
|
|
} else {
|
||
|
|
temp = (temp >>> 1);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
crc = (crc >>> 8) ^ temp;
|
||
|
|
}
|
||
|
|
|
||
|
|
// flip bits
|
||
|
|
return crc ^ -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Compute CRC with the help of a pre-calculated table.
|
||
|
|
*
|
||
|
|
* This supports append mode, if the second parameter is set.
|
||
|
|
*/
|
||
|
|
function crcTable(arr, append) {
|
||
|
|
var crc, i, l;
|
||
|
|
|
||
|
|
// if we're in append mode, don't reset crc
|
||
|
|
// if arr is null or undefined, reset table and return
|
||
|
|
if (typeof crcTable.crc === 'undefined' || !append || !arr) {
|
||
|
|
crcTable.crc = 0 ^ -1;
|
||
|
|
|
||
|
|
if (!arr) {
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// store in temp variable for minor speed gain
|
||
|
|
crc = crcTable.crc;
|
||
|
|
|
||
|
|
for (i = 0, l = arr.length; i < l; i += 1) {
|
||
|
|
crc = (crc >>> 8) ^ table[(crc ^ arr[i]) & 0xff];
|
||
|
|
}
|
||
|
|
|
||
|
|
crcTable.crc = crc;
|
||
|
|
|
||
|
|
return crc ^ -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
// build the table
|
||
|
|
// this isn't that costly, and most uses will be for table assisted mode
|
||
|
|
makeTable();
|
||
|
|
|
||
|
|
module.exports = function (val, direct) {
|
||
|
|
var val = (typeof val === 'string') ? strToArr(val) : val,
|
||
|
|
ret = direct ? crcDirect(val) : crcTable(val);
|
||
|
|
|
||
|
|
// convert to 2's complement hex
|
||
|
|
return (ret >>> 0).toString(16);
|
||
|
|
};
|
||
|
|
module.exports.direct = crcDirect;
|
||
|
|
module.exports.table = crcTable;
|
||
|
|
}());
|