javascript incremental crc32 naive implementation.

crc32-incremental.js

/**
 * javascript incremental crc32 naive implementation.
 * based on http://www.sunshine2k.de/articles/coding/crc/understanding_crc.html#ch44
 * not production ready, not efficient !
   
   dmeo:https://replit.com/join/dzezyxlpst-jaosnhsieh
 *
 *
 */

// get correct values from open source lib
const { crc32 } = require('crc');
const v1 = crc32(Buffer.from([0x01]));
const v2 = crc32(Buffer.from([0x02]), v1);
const v3 = crc32(Buffer.from([0x03]), v2);

console.log(`v1 ${v1} v2 ${v2} v3 ${v3}`);

//prepare own values
const tempCrc1 = getTempCrc32(Buffer.from([1]));
const vv1 = getFinalCrc(tempCrc1) >>> 0;
const tempCrc2 = getTempCrc32(Buffer.from([2]), tempCrc1);
const vv2 = getFinalCrc(tempCrc2) >>> 0;
const tempCrc3 = getTempCrc32(Buffer.from([3]), tempCrc2);
const vv3 = getFinalCrc(tempCrc3);

console.log(`vv1 ${vv1} vv2 ${vv2} vv3 ${vv3}`);

//test
const assert = require('assert');

assert(v1 === vv1, 'vv1 error');
console.log('vv1 passed!');
assert(v2, vv2, 'vv2 error');
console.log('vv2 passed!');
assert(v3, vv3, 'vv3 error');
console.log('vv3 passed!');

// below crc32 implementation

function getFinalCrc(tempCrc) {
  return ((libUtil_ReverseUint32(tempCrc) ^ 0xffffffff) & 0xffffffff) >>> 0;
}
function getTempCrc32(data = Buffer.from([]), previous = 0) {
  let crc = previous !== 0 ? previous : 0xffffffff;
  for (var j = 0; j < data.length; j++) {
    let bin = data[j];
    let revBin = libUtil_ReverseUint8(bin);
    crc ^= revBin << 24;

    for (var i = 0; i < 8; i++) {
      if (crc & 0x80000000) {
        crc = (crc << 1) ^ 0x04c11db7;
      } else {
        crc = crc << 1;
      }
      revBin <<= 1;
    }
  }
  return crc;
}

function libUtil_ReverseUint8(data = 0) {
  var rval = 0;
  var i = 0;
  for (i = 0; i < 8; i++) {
    if ((data & (1 << i)) != 0) {
      rval |= 0x80 >> i;
    }
  }
  return rval;
}

function libUtil_ReverseUint16(data = 0) {
  return (
    (libUtil_ReverseUint8(data & 0xff) << 8) |
    libUtil_ReverseUint8((data >> 8) & 0xff)
  );
}
function libUtil_ReverseUint32(data = 0) {
  return (
    (libUtil_ReverseUint16(data & 0xffff) << 16) |
    libUtil_ReverseUint16((data >> 16) & 0xffff)
  );
}