From 62bab2bf326db46389a9b3a3849dd0a61bb6dcc5 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Wed, 27 Apr 2016 20:14:36 -0700
Subject: [PATCH] O(n) sighashing.

---
 lib/bcoin/tx.js | 46 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index 5b5d7087..64728a57 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -468,13 +468,19 @@ TX.prototype.signatureHashV1 = function signatureHashV1(index, prev, type) {
   assert(prev instanceof Script);
 
   if (!(type & constants.hashType.ANYONECANPAY)) {
-    hashPrevouts = new BufferWriter();
-    for (i = 0; i < this.inputs.length; i++) {
-      prevout = this.inputs[i].prevout;
-      hashPrevouts.writeHash(prevout.hash);
-      hashPrevouts.writeU32(prevout.index);
+    if (this._hashPrevouts) {
+      hashPrevouts = this._hashPrevouts;
+    } else {
+      hashPrevouts = new BufferWriter();
+      for (i = 0; i < this.inputs.length; i++) {
+        prevout = this.inputs[i].prevout;
+        hashPrevouts.writeHash(prevout.hash);
+        hashPrevouts.writeU32(prevout.index);
+      }
+      hashPrevouts = utils.dsha256(hashPrevouts.render());
+      if (!this.mutable)
+        this._hashPrevouts = hashPrevouts;
     }
-    hashPrevouts = utils.dsha256(hashPrevouts.render());
   } else {
     hashPrevouts = utils.slice(constants.ZERO_HASH);
   }
@@ -482,20 +488,32 @@ TX.prototype.signatureHashV1 = function signatureHashV1(index, prev, type) {
   if (!(type & constants.hashType.ANYONECANPAY)
       && (type & 0x1f) !== constants.hashType.SINGLE
       && (type & 0x1f) !== constants.hashType.NONE) {
-    hashSequence = new BufferWriter();
-    for (i = 0; i < this.inputs.length; i++)
-      hashSequence.writeU32(this.inputs[i].sequence);
-    hashSequence = utils.dsha256(hashSequence.render());
+    if (this._hashSequence) {
+      hashSequence = this._hashSequence;
+    } else {
+      hashSequence = new BufferWriter();
+      for (i = 0; i < this.inputs.length; i++)
+        hashSequence.writeU32(this.inputs[i].sequence);
+      hashSequence = utils.dsha256(hashSequence.render());
+      if (!this.mutable)
+        this._hashSequence = hashSequence;
+    }
   } else {
     hashSequence = utils.slice(constants.ZERO_HASH);
   }
 
   if ((type & 0x1f) !== constants.hashType.SINGLE
       && (type & 0x1f) !== constants.hashType.NONE) {
-    hashOutputs = new BufferWriter();
-    for (i = 0; i < this.outputs.length; i++)
-      bcoin.protocol.framer.output(this.outputs[i], hashOutputs);
-    hashOutputs = utils.dsha256(hashOutputs.render());
+    if (this._hashOutputs) {
+      hashOutputs = this._hashOutputs;
+    } else {
+      hashOutputs = new BufferWriter();
+      for (i = 0; i < this.outputs.length; i++)
+        bcoin.protocol.framer.output(this.outputs[i], hashOutputs);
+      hashOutputs = utils.dsha256(hashOutputs.render());
+      if (!this.mutable)
+        this._hashOutputs = hashOutputs;
+    }
   } else if ((type & 0x1f) === constants.hashType.SINGLE && index < this.outputs.length) {
     hashOutputs = bcoin.protocol.framer.output(this.outputs[index]);
     hashOutputs = utils.dsha256(hashOutputs);