lz4js/util.js

An Lz4 implementation for the browser.

// Simple hash function, from: http://burtleburtle.net/bob/hash/integer.html.
// Chosen because it doesn't use multiply and achieves full avalanche.
exports.hashU32 = function hashU32 (a) {
  a = a | 0;
  a = a + 2127912214 + (a << 12) | 0;
  a = a ^ -949894596 ^ a >>> 19;
  a = a + 374761393 + (a << 5) | 0;
  a = a + -744332180 ^ a << 9;
  a = a + -42973499 + (a << 3) | 0;
  return a ^ -1252372727 ^ a >>> 16 | 0;
};

// Reads a 64-bit little-endian integer from an array.
exports.readU64 = function readU64 (b, n) {
  var x = 0;
  x |= b[n++] << 0;
  x |= b[n++] << 8;
  x |= b[n++] << 16;
  x |= b[n++] << 24;
  x |= b[n++] << 32;
  x |= b[n++] << 40;
  x |= b[n++] << 48;
  x |= b[n++] << 56;
  return x;
};

// Reads a 32-bit little-endian integer from an array.
exports.readU32 = function readU32 (b, n) {
  var x = 0;
  x |= b[n++] << 0;
  x |= b[n++] << 8;
  x |= b[n++] << 16;
  x |= b[n++] << 24;
  return x;
};

// Writes a 32-bit little-endian integer from an array.
exports.writeU32 = function writeU32 (b, n, x) {
  b[n++] = (x >> 0) & 0xff;
  b[n++] = (x >> 8) & 0xff;
  b[n++] = (x >> 16) & 0xff;
  b[n++] = (x >> 24) & 0xff;
};

// Multiplies two numbers using 32-bit integer multiplication.
// Algorithm from Emscripten.
exports.imul = function imul (a, b) {
  var ah = a >>> 16;
  var al = a & 65535;
  var bh = b >>> 16;
  var bl = b & 65535;

  return al * bl + (ah * bl + al * bh << 16) | 0;
};