add bn2.js.

lib/bcoin/bn.js

@@ -0,0 +1,98 @@
+/**
+ * bn.js - signed big numbers for bcoin
+ * Copyright (c) 2014-2015, Fedor Indutny (MIT License)
+ * https://github.com/indutny/bcoin
+ */
+
+var bn = require('bn.js');
+
+/**
+ * Signed Big Numbers
+ */
+
+function bn2(number, signed, base, endian) {
+  if (!(this instanceof bn2))
+    return new bn2(number, signed, base, endian);
+
+  if (typeof signed !== 'boolean') {
+    endian = base;
+    base = signed;
+    signed = null;
+  }
+
+  this.__signed = !!signed;
+
+  return bn.call(this, number, base, endian);
+}
+
+bn2.prototype.__proto__ = bn.prototype;
+
+bn2.prototype._initArray = function _initArray(number, base, endian) {
+  var i = 0;
+  var ret;
+
+  if (!this.__signed)
+    return bn.prototype._initArray.apply(this, arguments);
+
+  if (endian === 'le')
+    i = number.length - 1;
+
+  // If we are signed, do (~num + 1) to get
+  // the positive counterpart and set bn's
+  // negative flag.
+  if (number[i] & 0x80) {
+    if (isNegZero(number, endian)) {
+      ret = this._initNumber(0, 10, endian);
+    } else {
+      ret = bn.prototype._initArray.apply(this, arguments);
+      this.inotn(64).iaddn(1).ineg();
+    }
+  } else {
+    ret = bn.prototype._initArray.apply(this, arguments);
+  }
+
+  return ret;
+};
+
+bn2.prototype.toArray = function toArray(endian, length) {
+  var self = this;
+
+  if (!this.__signed)
+    return bn.prototype.toArray.apply(self, arguments);
+
+  // Convert the number to the
+  // negative byte representation.
+  if (self.isNeg()) {
+    if (self.cmpn(0) === 0)
+      self = new bn(0);
+    else
+      self = self.neg().notn(64).addn(1);
+  }
+
+  return bn.prototype.toArray.apply(self, arguments);
+};
+
+bn2.signed = function signed(number, base, endian) {
+  return new bn2(number, true, base, endian);
+};
+
+function isNegZero(number, endian) {
+  var i = 0;
+
+  if (endian === 'le')
+    i = number.length - 1;
+
+  if (number[i] & 0x80) {
+    number = number.slice();
+    number[i] &= ~0x80;
+    return new bn(number, endian).cmpn(0) === 0;
+  }
+
+  return false;
+}
+
+/**
+ * Expose
+ */
+
+module.exports = bn2;