Merge branch 'rabin-fingerprint'

buffer.js

@@ -113,3 +113,20 @@ export const encodeAny = data => {
  * @return {any}
  */
 export const decodeAny = buf => decoding.readAny(decoding.createDecoder(buf))
+
+/**
+ * Shift Byte Array {N} bits to the left. Does not expand byte array.
+ *
+ * @param {Uint8Array} bs
+ * @param {number} N should be in the range of [0-7]
+ */
+export const shiftNBitsLeft = (bs, N) => {
+  if (N === 0) return bs
+  bs = new Uint8Array(bs)
+  bs[0] <<= N
+  for (let i = 1; i < bs.length; i++) {
+    bs[i - 1] |= bs[i] >>> (8 - N)
+    bs[i] <<= N
+  }
+  return bs
+}

checksum.js

@@ -0,0 +1,28 @@
+import * as buffer from './buffer.js'
+
+/**
+ * Little endian table
+ * @type {Uint8Array | null}
+ */
+let _crc32Table = null
+const _computeCrc32Table = () => {
+  if (_crc32Table == null) {
+    _crc32Table = buffer.createUint8ArrayFromLen(32)
+  }
+  let i = 128
+  let crc = 1
+  do {
+    if ((crc & 1) > 0) { // @todo this could be optimized
+      crc = (crc >>> 1) ^ 0x8408
+    } else {
+      crc >>>= 1
+    }
+    for (let j = 0; j < 256; j = j * i) {
+      _crc32Table[i + j] = crc ^ _crc32Table[j]
+    }
+    i >>>= 1
+  } while (i > 0)
+  return _crc32Table
+}
+
+console.log(_computeCrc32Table())