From ec84e81e8383b3b1e1ef4a6dbcb088193d8de5d7 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <sipa@ulyssis.org>
Date: Mon, 24 Jun 2013 20:51:08 +0200
Subject: [PATCH] Prune provably-unspendable outputs

---
 src/core.h   | 8 +++++++-
 src/script.h | 7 +++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/core.h b/src/core.h
index 1b9d4dd765..a8828324fa 100644
--- a/src/core.h
+++ b/src/core.h
@@ -389,7 +389,13 @@ public:
     int nVersion;
 
     // construct a CCoins from a CTransaction, at a given height
-    CCoins(const CTransaction &tx, int nHeightIn) : fCoinBase(tx.IsCoinBase()), vout(tx.vout), nHeight(nHeightIn), nVersion(tx.nVersion) { }
+    CCoins(const CTransaction &tx, int nHeightIn) : fCoinBase(tx.IsCoinBase()), vout(tx.vout), nHeight(nHeightIn), nVersion(tx.nVersion) {
+        BOOST_FOREACH(CTxOut &txout, vout) {
+            if (txout.scriptPubKey.IsUnspendable())
+                txout.SetNull();
+        }
+        Cleanup();
+    }
 
     // empty constructor
     CCoins() : fCoinBase(false), vout(0), nHeight(0), nVersion(0) { }
diff --git a/src/script.h b/src/script.h
index 03afe8b652..2dc0697ade 100644
--- a/src/script.h
+++ b/src/script.h
@@ -548,6 +548,13 @@ public:
         return true;
     }
 
+    // Returns whether the script is guaranteed to fail at execution,
+    // regardless of the initial stack. This allows outputs to be pruned
+    // instantly when entering the UTXO set.
+    bool IsUnspendable() const
+    {
+        return (size() > 0 && *begin() == OP_RETURN);
+    }
 
     void SetDestination(const CTxDestination& address);
     void SetMultisig(int nRequired, const std::vector<CPubKey>& keys);