Added crc32 implementation

lib/zlib/crc32.js

@@ -0,0 +1,34 @@
+'use strict';
+
+// CRC table.
+// Use ordinary array, since untyped makes no boost here
+//
+var crcTable = function makeTable() {
+  var c, table = [];
+
+  for(var n =0; n < 256; n++){
+    c = n;
+    for(var k =0; k < 8; k++){
+      c = ((c&1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
+    }
+    table[n] = c;
+  }
+
+  return table;
+} ();
+
+
+function crc32(crc, buf, len, pos) {
+  var t = crcTable,
+    , end = pos + len
+    , crc = 0 ^ (-1);
+
+  for (var i = pos; i < end; i++ ) {
+    crc = (crc >>> 8) ^ t[(crc ^ input[i]) & 0xFF];
+  }
+
+  return (crc ^ (-1)); // >>> 0;
+}
+
+
+module.exports = crc32;