Implement crc32 with Buffer

Probable fix for issue #13

lib/crc32.js

@@ -1,5 +1,13 @@
 "use strict";
 
+// ARMv6 (Raspberry Pi) has bug in bitwise operations
+// https://code.google.com/p/v8/issues/detail?id=3757
+// https://github.com/alexeyten/qr-image/issues/13
+if (process.arch === 'arm') {
+    module.exports = require('./crc32buffer');
+    return;
+}
+
 var crc_table = [];
 
 (function() {

lib/crc32buffer.js

@@ -0,0 +1,50 @@
+'use strict';
+
+var crc_table = [];
+
+for (var n = 0; n < 256; n++) {
+    var c = crc_table[n] = Buffer(4);
+    c.writeUInt32BE(n, 0);
+
+    for (var k = 0; k < 8; k++) {
+        var b0 = c[0] & 1;
+        var b1 = c[1] & 1;
+        var b2 = c[2] & 1;
+        var b3 = c[3] & 1;
+
+        c[0] = (c[0] >> 1) ^ (b3 ? 0xed : 0);
+        c[1] = (c[1] >> 1) ^ (b3 ? 0xb8 : 0) ^ (b0 ? 0x80 : 0);
+        c[2] = (c[2] >> 1) ^ (b3 ? 0x83 : 0) ^ (b1 ? 0x80 : 0);
+        c[3] = (c[3] >> 1) ^ (b3 ? 0x20 : 0) ^ (b2 ? 0x80 : 0);
+    }
+}
+
+function update(c, buf) {
+    var l = buf.length;
+    for (var n = 0; n < l; n++) {
+        var e = crc_table[c[3] ^ buf[n]];
+        c[3] = e[3] ^ c[2];
+        c[2] = e[2] ^ c[1];
+        c[1] = e[1] ^ c[0];
+        c[0] = e[0];
+    }
+}
+
+function crc32(/* arguments */) {
+    var l = arguments.length;
+    var c = Buffer(4);
+    c.fill(0xff);
+
+    for (var i = 0; i < l; i++) {
+        update(c, Buffer(arguments[i]));
+    }
+
+    c[0] = c[0] ^ 0xff;
+    c[1] = c[1] ^ 0xff;
+    c[2] = c[2] ^ 0xff;
+    c[3] = c[3] ^ 0xff;
+
+    return c.readUInt32BE(0);
+}
+
+module.exports = crc32;