From a057dc4064817dd12f6264ef6fb94062d24757b0 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Wed, 23 Dec 2015 02:42:36 -0800
Subject: [PATCH] use big numbers when calculating fee.

---
 lib/bcoin/tx.js | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index 025fbe5c..f854ad1b 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -649,7 +649,7 @@ TX.prototype.maxSize = function maxSize() {
     }
   }, this);
 
-  return size;
+  return new bn(size);
 };
 
 TX.prototype.utxos = function utxos(unspent) {
@@ -657,10 +657,10 @@ TX.prototype.utxos = function utxos(unspent) {
   var cost = this.funds('out');
 
   // Use initial fee for starters
-  var fee = 1;
+  var fee = new bn(1);
 
   // total = cost + fee
-  var total = cost.add(new bn(TX.fee));
+  var total = cost.addn(TX.fee);
 
   var inputs = this.inputs.slice();
   var utxos = [];
@@ -691,9 +691,11 @@ TX.prototype.utxos = function utxos(unspent) {
     // Calculate maximum possible size after signing
     byteSize = this.maxSize();
 
-    addFee = Math.ceil(byteSize / 1024) - fee;
-    total.iadd(new bn(addFee * TX.fee));
-    fee += addFee;
+    addFee = byteSize.modn(1024) === 0
+      ? byteSize.divn(1024).sub(fee)
+      : byteSize.divn(1024).addn(1).sub(fee);
+    total.iadd(addFee.muln(TX.fee));
+    fee.iadd(addFee);
 
     // Failed to get enough funds, add more inputs
     if (this.funds('in').cmp(total) < 0)
@@ -765,24 +767,26 @@ TX.prototype._recalculateFee = function recalculateFee() {
   }
 
   var byteSize = this.maxSize();
-  var newFee = Math.ceil(byteSize / 1024) * TX.fee;
-  var currentFee = this.getFee().toNumber();
+  var newFee = byteSize.modn(1024) === 0
+    ? byteSize.divn(1024).muln(TX.fee)
+    : byteSize.divn(1024).addn(1).muln(TX.fee);
+  var currentFee = this.getFee();
 
-  if (newFee === currentFee) {
+  if (newFee.cmp(currentFee) === 0) {
     if (!this.changeOutput)
       this.outputs.pop();
     return;
   }
 
-  if (newFee > currentFee) {
-    if (output.value.cmpn(newFee - currentFee) < 0) {
+  if (newFee.cmp(currentFee) > 0) {
+    if (output.value.cmp(newFee.sub(currentFee)) < 0) {
       this.outputs.pop();
       this.changeOutput = null;
       return;
     }
-    output.value.isubn(newFee - currentFee);
+    output.value.isub(newFee.sub(currentFee));
   } else {
-    output.value.iaddn(currentFee - newFee);
+    output.value.iadd(currentFee.sub(newFee));
   }
 
   if (output.value.cmpn(TX.dust) < 0) {