From cde44d689c3b8357f2e7a59ceb216687d293746f Mon Sep 17 00:00:00 2001
From: "Ryan X. Charles" <ryan@bitpay.com>
Date: Wed, 20 Aug 2014 12:35:55 -0700
Subject: [PATCH] fix precision error by handling BNs correctly

---
 lib/bufferreader.js       | 41 ++++++++++++++++++++++-------------
 test/test.bufferreader.js | 45 ++++++++++++++++++++++++++++++++-------
 2 files changed, 63 insertions(+), 23 deletions(-)

diff --git a/lib/bufferreader.js b/lib/bufferreader.js
index fc06b17..afee08f 100644
--- a/lib/bufferreader.js
+++ b/lib/bufferreader.js
@@ -1,3 +1,5 @@
+var BN = require('./bn');
+
 var BufferReader = function BufferReader(buf, pos) {
   if (!(this instanceof BufferReader))
     return new BufferReader(buf);
@@ -45,24 +47,19 @@ BufferReader.prototype.readUInt32LE = function() {
   return val;
 };
 
-//TODO: What if n is so large that it loses precision?
-BufferReader.prototype.readUInt64BE = function() {
-  var val = 0;
-  for (var i = 0; i < 8; i++) {
-    val += Math.pow(256, i) * this.buf[this.pos + 8 - 1 - i];
-  }
+BufferReader.prototype.readUInt64BEBN = function() {
+  var buf = this.buf.slice(this.pos, this.pos + 8);
+  var bn = BN().fromBuffer(buf);
   this.pos = this.pos + 8;
-  return val;
+  return bn;
 };
 
-//TODO: What if n is so large that it loses precision?
-BufferReader.prototype.readUInt64LE = function() {
-  var val = 0;
-  for (var i = 0; i < 8; i++) {
-    val += Math.pow(256, i) * this.buf[this.pos + i];
-  }
+BufferReader.prototype.readUInt64LEBN = function() {
+  var buf = this.buf.slice(this.pos, this.pos + 8);
+  var reversebuf = BufferReader(buf).reverse().read();
+  var bn = BN().fromBuffer(reversebuf);
   this.pos = this.pos + 8;
-  return val;
+  return bn;
 };
 
 BufferReader.prototype.readVarInt = function() {
@@ -73,12 +70,26 @@ BufferReader.prototype.readVarInt = function() {
     case 0xFE:
       return this.readUInt32LE();
     case 0xFF:
-      return this.readUInt64LE();
+      return this.readUInt64LEBN().toNumber();
     default:
       return first;
   }
 };
 
+BufferReader.prototype.readVarIntBN = function() {
+  var first = this.readUInt8();
+  switch (first) {
+    case 0xFD:
+      return BN(this.readUInt16LE());
+    case 0xFE:
+      return BN(this.readUInt32LE());
+    case 0xFF:
+      return this.readUInt64LEBN();
+    default:
+      return BN(first);
+  }
+};
+
 BufferReader.prototype.reverse = function() {
   var buf = new Buffer(this.buf.length);
   for (var i = 0; i < buf.length; i++)
diff --git a/test/test.bufferreader.js b/test/test.bufferreader.js
index bca7b63..f305ecd 100644
--- a/test/test.bufferreader.js
+++ b/test/test.bufferreader.js
@@ -82,33 +82,33 @@ describe('BufferReader', function() {
 
   });
 
-  describe('#readUInt64BE', function() {
+  describe('#readUInt64BEBN', function() {
 
     it('should return 1', function() {
       var buf = new Buffer(8);
       buf.fill(0);
       buf.writeUInt32BE(1, 4);
       var br = new BufferReader(buf);
-      br.readUInt64BE().should.equal(1);
+      br.readUInt64BEBN().toNumber().should.equal(1);
     });
 
     it('should return 2^64', function() {
       var buf = new Buffer(8);
       buf.fill(0xff);
       var br = new BufferReader(buf);
-      br.readUInt64BE().should.equal(Math.pow(2, 64));
+      br.readUInt64BEBN().toNumber().should.equal(Math.pow(2, 64));
     });
 
   });
 
-  describe('#readUInt64LE', function() {
+  describe('#readUInt64LEBN', function() {
 
     it('should return 1', function() {
       var buf = new Buffer(8);
       buf.fill(0);
       buf.writeUInt32LE(1, 0);
       var br = new BufferReader(buf);
-      br.readUInt64LE().should.equal(1);
+      br.readUInt64LEBN().toNumber().should.equal(1);
     });
 
     it('should return 2^30', function() {
@@ -116,21 +116,21 @@ describe('BufferReader', function() {
       buf.fill(0);
       buf.writeUInt32LE(Math.pow(2, 30), 0);
       var br = new BufferReader(buf);
-      br.readUInt64LE().should.equal(Math.pow(2, 30));
+      br.readUInt64LEBN().toNumber().should.equal(Math.pow(2, 30));
     });
 
     it('should return 0', function() {
       var buf = new Buffer(8);
       buf.fill(0);
       var br = new BufferReader(buf);
-      br.readUInt64LE().should.equal(0);
+      br.readUInt64LEBN().toNumber().should.equal(0);
     });
 
     it('should return 2^64', function() {
       var buf = new Buffer(8);
       buf.fill(0xff);
       var br = new BufferReader(buf);
-      br.readUInt64LE().should.equal(Math.pow(2, 64));
+      br.readUInt64LEBN().toNumber().should.equal(Math.pow(2, 64));
     });
 
   });
@@ -164,6 +164,35 @@ describe('BufferReader', function() {
 
   });
 
+  describe('#readVarIntBN', function() {
+
+    it('should read a 1 byte varint', function() {
+      var buf = new Buffer([50]);
+      var br = new BufferReader(buf);
+      br.readVarIntBN().toNumber().should.equal(50);
+    });
+
+    it('should read a 3 byte varint', function() {
+      var buf = new Buffer([253, 253, 0]);
+      var br = new BufferReader(buf);
+      br.readVarIntBN().toNumber().should.equal(253);
+    });
+
+    it('should read a 5 byte varint', function() {
+      var buf = new Buffer([254, 0, 0, 0, 0]);
+      buf.writeUInt32LE(50000, 1);
+      var br = new BufferReader(buf);
+      br.readVarIntBN().toNumber().should.equal(50000);
+    });
+
+    it('should read a 9 byte varint', function() {
+      var buf = Buffer.concat([new Buffer([255]), new Buffer('ffffffffffffffff', 'hex')]);
+      var br = new BufferReader(buf);
+      br.readVarIntBN().toNumber().should.equal(Math.pow(2, 64));
+    });
+
+  });
+
   describe('#reverse', function() {
     
     it('should reverse this [0, 1]', function() {