From ce650182f4d9847423202789856e6e5f499151f8 Mon Sep 17 00:00:00 2001
From: Suhas Daftuar <sdaftuar@chaincode.com>
Date: Tue, 12 Sep 2017 11:38:20 -0400
Subject: [PATCH] Use P2SH consensus rules for all blocks

This commit moves P2SH activation back to the genesis block, with
a hardcoded exception for the one historical block in the chain that
violated this rule.
---
 src/chainparams.cpp    |  6 +++---
 src/consensus/params.h |  4 ++--
 src/validation.cpp     | 11 +++++++++--
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 6067503b0b9..121d95af90c 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -75,7 +75,7 @@ public:
     CMainParams() {
         strNetworkID = "main";
         consensus.nSubsidyHalvingInterval = 210000;
-        consensus.BIP16Height = 173805; // 00000000000000ce80a7e057163a4db1d5ad7b20fb6f598c9597b9665c8fb0d4 - April 1, 2012
+        consensus.BIP16Exception = uint256S("0x00000000000002dc756eebf4f49723ed8d30cc28a5f108eb94b1ba88ac4f9c22");
         consensus.BIP34Height = 227931;
         consensus.BIP34Hash = uint256S("0x000000000000024b89b42a942fe0d9fea3bb44ab7bd1b19115dd6a759c0808b8");
         consensus.BIP65Height = 388381; // 000000000000000004c2b624ed5d7756c508d90fd0da2c7c679febfa6c4735f0
@@ -190,7 +190,7 @@ public:
     CTestNetParams() {
         strNetworkID = "test";
         consensus.nSubsidyHalvingInterval = 210000;
-        consensus.BIP16Height = 514; // 00000000040b4e986385315e14bee30ad876d8b47f748025b26683116d21aa65
+        consensus.BIP16Exception = uint256S("0x00000000dd30457c001f4095d208cc1296b0eed002427aa599874af7a432b105");
         consensus.BIP34Height = 21111;
         consensus.BIP34Hash = uint256S("0x0000000023b3a96d3484e5abb3755c413e7d41500f8e2a5c3f0dd01299cd8ef8");
         consensus.BIP65Height = 581885; // 00000000007f6655f22f98e72ed80d8b06dc761d5da09df0fa1dc4be4f861eb6
@@ -283,7 +283,7 @@ public:
     CRegTestParams() {
         strNetworkID = "regtest";
         consensus.nSubsidyHalvingInterval = 150;
-        consensus.BIP16Height = 0; // always enforce P2SH BIP16 on regtest
+        consensus.BIP16Exception = uint256();
         consensus.BIP34Height = 100000000; // BIP34 has not activated on regtest (far in the future so block v1 are not rejected in tests)
         consensus.BIP34Hash = uint256();
         consensus.BIP65Height = 1351; // BIP65 activated on regtest (Used in rpc activation tests)
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 4ef808c8566..0559304fc2d 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -49,8 +49,8 @@ struct BIP9Deployment {
 struct Params {
     uint256 hashGenesisBlock;
     int nSubsidyHalvingInterval;
-    /** Block height at which BIP16 becomes active */
-    int BIP16Height;
+    /* Block hash that is excepted from BIP16 enforcement */
+    uint256 BIP16Exception;
     /** Block height and hash at which BIP34 becomes active */
     int BIP34Height;
     uint256 BIP34Hash;
diff --git a/src/validation.cpp b/src/validation.cpp
index cbbc857fdcf..ac585895e54 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1730,8 +1730,15 @@ static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consens
 
     unsigned int flags = SCRIPT_VERIFY_NONE;
 
-    // Start enforcing P2SH (BIP16)
-    if (pindex->nHeight >= consensusparams.BIP16Height) {
+    // BIP16 didn't become active until Apr 1 2012 (on mainnet, and
+    // retroactively applied to testnet)
+    // However, only one historical block violated the P2SH rules (on both
+    // mainnet and testnet), so for simplicity, always leave P2SH
+    // on except for the one violating block.
+    if (consensusparams.BIP16Exception.IsNull() || // no bip16 exception on this chain
+        pindex->phashBlock == nullptr || // this is a new candidate block, eg from TestBlockValidity()
+        *pindex->phashBlock != consensusparams.BIP16Exception) // this block isn't the historical exception
+    {
         flags |= SCRIPT_VERIFY_P2SH;
     }