From 5cb23020ff3f168f7a93c6a98b40a0ba6e0c4ce0 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sat, 2 Jul 2016 17:20:46 -0700
Subject: [PATCH] implement coin spent field.

---
 lib/bcoin/coins.js | 40 ++++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/lib/bcoin/coins.js b/lib/bcoin/coins.js
index 8311fe11..10ba7cda 100644
--- a/lib/bcoin/coins.js
+++ b/lib/bcoin/coins.js
@@ -177,9 +177,9 @@ Coins.prototype.getLength = function getLength() {
  * Coins serialization:
  * version: varint
  * bits: varint ((height << 1) | coinbase-flag)
+ * spent-field: varint size | bitmap (0=unspent, 1=spent)
  * outputs (repeated):
- *   prefix: 0xff = spent
- *           0x00 = varint size | raw script
+ *   prefix: 0x00 = varint size | raw script
  *           0x01 = 20 byte pubkey hash
  *           0x02 = 20 byte script hash
  *           0x03 = 33 byte compressed key
@@ -197,7 +197,7 @@ Coins.prototype.toRaw = function toRaw(writer) {
   var p = new BufferWriter(writer);
   var height = this.height;
   var length = this.getLength();
-  var i, output, prefix, data, bits;
+  var i, output, prefix, data, bits, field, pos, bit, oct;
 
   // Unfortunately, we don't have a compact
   // way to store unconfirmed height.
@@ -215,13 +215,25 @@ Coins.prototype.toRaw = function toRaw(writer) {
   p.writeVarint(this.version);
   p.writeVarint(bits);
 
+  field = new Buffer(Math.ceil(length / 8));
+  field.fill(0);
+  pos = 0;
+
+  for (i = 0; i < length; i++) {
+    output = this.outputs[i] ? 0 : 1;
+    bit = pos % 8;
+    oct = (pos - bit) / 8;
+    field[oct] |= output << (7 - bit);
+    pos++;
+  }
+
+  p.writeVarBytes(field);
+
   for (i = 0; i < length; i++) {
     output = this.outputs[i];
 
-    if (!output) {
-      p.writeU8(0xff);
+    if (!output)
       continue;
-    }
 
     if (output instanceof CompressedCoin) {
       p.writeBytes(output.toRaw());
@@ -280,7 +292,7 @@ Coins.prototype.toRaw = function toRaw(writer) {
 Coins.prototype.fromRaw = function fromRaw(data, hash, index) {
   var p = new BufferReader(data);
   var i = 0;
-  var bits, coin, prefix, offset, size;
+  var bits, coin, prefix, offset, size, field, bit, oct, spent;
 
   this.version = p.readVarint();
 
@@ -293,14 +305,15 @@ Coins.prototype.fromRaw = function fromRaw(data, hash, index) {
   if (this.height === 0x7fffffff)
     this.height = -1;
 
+  field = p.readVarBytes(true);
+
   while (p.left()) {
-    offset = p.start();
-    prefix = p.readU8();
+    bit = i % 8;
+    oct = (i - bit) / 8;
+    spent = (field[oct] >>> (7 - bit)) & 1;
 
     // Already spent.
-    if (prefix === 0xff) {
-      p.end();
-
+    if (spent) {
       // Don't bother pushing outputs on if
       // we're seeking to a specific index.
       if (index != null) {
@@ -315,6 +328,9 @@ Coins.prototype.fromRaw = function fromRaw(data, hash, index) {
       continue;
     }
 
+    offset = p.start();
+    prefix = p.readU8();
+
     // Skip past the compressed scripts.
     switch (prefix & 3) {
       case 0: