support BN in bufferwriter

So that the precision of writing a variable sized integer is sufficient.

lib/bufferwriter.js

@@ -1,3 +1,5 @@
+var BN = require('./bn');
+
 var BufferWriter = function BufferWriter(bufs) {
   if (!(this instanceof BufferWriter))
     return new BufferReader(buf);
@@ -48,21 +50,17 @@ BufferWriter.prototype.writeUInt32LE = function(n) {
   return this;
 };
 
-//TODO: What if n is so large that it loses precision?
+BufferWriter.prototype.writeUInt64BEBN = function(bn) {
-BufferWriter.prototype.writeUInt64BE = function(n) {
+  var buf = bn.toBuffer({size: 8});
-  var buf = new Buffer(8);
-  buf.writeInt32BE(n & -1, 4);
-  buf.writeUInt32BE(Math.floor(n / 0x100000000), 0);
   this.write(buf);
   return this;
 };
 
 //TODO: What if n is so large that it loses precision?
-BufferWriter.prototype.writeUInt64LE = function(n) {
+BufferWriter.prototype.writeUInt64LEBN = function(bn) {
-  var buf = new Buffer(8);
+  var buf = bn.toBuffer({size: 8});
-  buf.writeInt32LE(n & -1, 0);
+  var reversebuf = new Buffer(Array.apply(new Array(), buf).reverse());
-  buf.writeUInt32LE(Math.floor(n / 0x100000000), 4);
+  this.write(reversebuf);
-  this.write(buf);
   return this;
 };
 
@@ -72,6 +70,12 @@ BufferWriter.prototype.writeVarInt = function(n) {
   return this;
 };
 
+BufferWriter.prototype.writeVarIntBN = function(bn) {
+  var buf = BufferWriter.varIntBufBN(bn);
+  this.write(buf);
+  return this;
+};
+
 //TODO: What if n is so large that it loses precision?
 BufferWriter.varIntBuf = function(n) {
   var buf = undefined;
@@ -95,4 +99,27 @@ BufferWriter.varIntBuf = function(n) {
   return buf;
 };
 
+BufferWriter.varIntBufBN = function(bn) {
+  var buf = undefined;
+    var n = bn.toNumber();
+  if (n < 253) {
+    buf = new Buffer(1);
+    buf.writeUInt8(n, 0);
+  } else if (n < 0x10000) {
+    buf = new Buffer(1 + 2);
+    buf.writeUInt8(253, 0);
+    buf.writeUInt16LE(n, 1);
+  } else if (n < 0x100000000) {
+    buf = new Buffer(1 + 4);
+    buf.writeUInt8(254, 0);
+    buf.writeUInt32LE(n, 1);
+  } else {
+    var bw = new BufferWriter();
+    bw.writeUInt8(255);
+    bw.writeUInt64LEBN(bn);
+    var buf = bw.concat();
+  }
+  return buf;
+};
+
 module.exports = BufferWriter;

test/test.bufferwriter.js

@@ -1,4 +1,5 @@
 var BufferWriter = require('../lib/bufferwriter');
+var BN = require('../lib/bn');
 var should = require('chai').should();
 
 describe('BufferWriter', function() {
@@ -75,20 +76,20 @@ describe('BufferWriter', function() {
 
   });
 
-  describe('#writeUInt64BE', function() {
+  describe('#writeUInt64BEBN', function() {
     
     it('should write 1', function() {
       var bw = new BufferWriter();
-      bw.writeUInt64BE(1).concat().toString('hex').should.equal('0000000000000001');
+      bw.writeUInt64BEBN(BN(1)).concat().toString('hex').should.equal('0000000000000001');
     });
 
   });
 
-  describe('#writeUInt64LE', function() {
+  describe('#writeUInt64LEBN', function() {
     
     it('should write 1', function() {
       var bw = new BufferWriter();
-      bw.writeUInt64LE(1).concat().toString('hex').should.equal('0100000000000000');
+      bw.writeUInt64LEBN(BN(1)).concat().toString('hex').should.equal('0100000000000000');
     });
 
   });
@@ -121,4 +122,32 @@ describe('BufferWriter', function() {
 
   });
 
+  describe('#writeVarIntBN', function() {
+    
+    it('should write a 1 byte varInt', function() {
+      var bw = new BufferWriter();
+      bw.writeVarIntBN(BN(1));
+      bw.concat().length.should.equal(1);
+    });
+
+    it('should write a 3 byte varInt', function() {
+      var bw = new BufferWriter();
+      bw.writeVarIntBN(BN(1000));
+      bw.concat().length.should.equal(3);
+    });
+
+    it('should write a 5 byte varInt', function() {
+      var bw = new BufferWriter();
+      bw.writeVarIntBN(BN(Math.pow(2, 16 + 1)));
+      bw.concat().length.should.equal(5);
+    });
+
+    it('should write a 9 byte varInt', function() {
+      var bw = new BufferWriter();
+      bw.writeVarIntBN(BN(Math.pow(2, 32 + 1)));
+      bw.concat().length.should.equal(9);
+    });
+
+  });
+
 });