From 3ff4dc99ad015f626e66e353a1f2ff0ff4e93030 Mon Sep 17 00:00:00 2001
From: JoelKatz <DavidJoelSchwartz@GMail.com>
Date: Fri, 28 Dec 2012 20:40:30 -0800
Subject: [PATCH] Function to retrieve previous ledger hashes from the ledger.

---
 src/cpp/ripple/Ledger.cpp | 42 +++++++++++++++++++++++++++++++--------
 src/cpp/ripple/Ledger.h   |  1 +
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/src/cpp/ripple/Ledger.cpp b/src/cpp/ripple/Ledger.cpp
index 185f5d983..75bac9ba4 100644
--- a/src/cpp/ripple/Ledger.cpp
+++ b/src/cpp/ripple/Ledger.cpp
@@ -647,14 +647,6 @@ Json::Value Ledger::getJson(int options)
 		}
 		ledger["accountState"] = state;
 	}
-	if (mAccountStateMap && ((options & LEDGER_JSON_HISTORY) != 0))
-	{
-		SLE::pointer hashIndex = getSLE(getLedgerHashIndex());
-		if (hashIndex)
-			ledger["previousHashes"] = hashIndex->getJson(0);
-		else
-			ledger["previousHashes"] = "missing";
-	}
 	ledger["seqNum"] = boost::lexical_cast<std::string>(mLedgerSeq);
 	return ledger;
 }
@@ -962,6 +954,40 @@ int Ledger::getLedgerHashOffset(uint32 desiredLedgerIndex, uint32 currentLedgerI
 	return currentLedgerIndex - desiredLedgerIndex - 1;
 }
 
+uint256 Ledger::getLedgerHash(uint32 ledgerIndex)
+{ // return the hash of the specified ledger, 0 if not available
+
+	// easy cases
+	if (ledgerIndex > mLedgerSeq)
+		return uint256();
+	if (ledgerIndex == mLedgerSeq)
+		return getHash();
+	if (ledgerIndex == (mLedgerSeq - 1))
+		return mParentHash;
+
+	// within 255
+	int offset = getLedgerHashOffset(ledgerIndex, mLedgerSeq);
+	if (offset != -1)
+	{
+		SLE::pointer hashIndex = getSLE(getLedgerHashIndex());
+		if (hashIndex)
+			return hashIndex->getFieldV256(sfHashes).peekValue().at(offset);
+		else
+			assert(false);
+	}
+
+	if ((ledgerIndex & 0xff) != 0)
+		return uint256();
+
+	SLE::pointer hashIndex = getSLE(getLedgerHashIndex(ledgerIndex));
+	if (hashIndex)
+		return hashIndex->getFieldV256(sfHashes).peekValue().at(getLedgerHashOffset(ledgerIndex, mLedgerSeq));
+	else
+		assert(false);
+
+	return uint256();
+}
+
 uint256 Ledger::getBookBase(const uint160& uTakerPaysCurrency, const uint160& uTakerPaysIssuerID,
 	const uint160& uTakerGetsCurrency, const uint160& uTakerGetsIssuerID)
 {
diff --git a/src/cpp/ripple/Ledger.h b/src/cpp/ripple/Ledger.h
index 741177b05..b9cf05892 100644
--- a/src/cpp/ripple/Ledger.h
+++ b/src/cpp/ripple/Ledger.h
@@ -198,6 +198,7 @@ public:
 	static uint256 getLedgerHashIndex(uint32 desiredLedgerIndex);
 	static int getLedgerHashOffset(uint32 desiredLedgerIndex);
 	static int getLedgerHashOffset(uint32 desiredLedgerIndex, uint32 currentLedgerIndex);
+	uint256 getLedgerHash(uint32 ledgerIndex);
 
 	static uint256 getLedgerFeatureIndex();
 	static uint256 getLedgerFeeIndex();