First Commit

qr/errorcode.js

@@ -0,0 +1,77 @@
+"use strict";
+
+// {{{1 Galois Field Math
+var GF256_BASE = 285;
+
+var EXP_TABLE = [1];
+var LOG_TABLE = [];
+
+for (var i = 1; i < 256; i++) {
+    var n = EXP_TABLE[i - 1] << 1;
+    if (n > 255) n = n ^ GF256_BASE;
+    EXP_TABLE[i] = n;
+}
+
+for (var i = 0; i < 255; i++) {
+    LOG_TABLE[EXP_TABLE[i]] = i;
+}
+
+function exp(k) {
+    while (k < 0) k += 255;
+    while (k > 255) k -= 255;
+    return EXP_TABLE[k];
+}
+
+function log(k) {
+    if (k < 1 || k > 255) {
+        throw Error('Bad log(' + k + ')');
+    }
+    return LOG_TABLE[k];
+}
+
+// {{{1 Generator Polynomials
+var POLYNOMIALS = [
+    [0], // a^0 x^0
+    [0, 0], // a^0 x^1 + a^0 x^0
+    [0, 25, 1], // a^0 x^2 + a^25 x^1 + a^1 x^0
+    // and so on...
+];
+
+function generatorPolynomial(num) {
+    if (POLYNOMIALS[num]) {
+        return POLYNOMIALS[num];
+    }
+    var prev = generatorPolynomial(num - 1);
+    var res = [];
+
+    res[0] = prev[0];
+    for (var i = 1; i <= num; i++) {
+        res[i] = log(exp(prev[i]) ^ exp(prev[i - 1] + num - 1));
+    }
+    POLYNOMIALS[num] = res;
+    return res;
+}
+
+// {{{1 export functions
+module.exports = function calculate_ec(msg, ec_len) {
+    // `msg` could be array or buffer
+    // convert `msg` to array
+    msg = [].slice.call(msg);
+
+    // Generator Polynomial
+    var poly = generatorPolynomial(ec_len);
+
+    for (var i = 0; i < ec_len; i++) msg.push(0);
+    while (msg.length > ec_len) {
+        if (!msg[0]) {
+            msg.shift();
+            continue;
+        }
+        var log_k = log(msg[0]);
+        for (var i = 0; i <= ec_len; i++) {
+            msg[i] = msg[i] ^ exp(poly[i] + log_k);
+        }
+        msg.shift();
+    }
+    return Buffer.from(msg);
+}