Implement SequenceLocks functions

SequenceLocks functions are used to evaluate sequence lock times or heights per BIP 68.

The majority of this code is copied from maaku in #6312
Further credit: btcdrak, sipa, NicolasDorier

2 files changed, 31 insertions, 9 deletions

diff --git a/src/primitives/transaction.cpp b/src/primitives/transaction.cpp
index 46d3cbbe2e..7d0b208398 100644
--- a/src/primitives/transaction.cpp
+++ b/src/primitives/transaction.cpp
@@ -37,7 +37,7 @@ std::string CTxIn::ToString() const
         str += strprintf(", coinbase %s", HexStr(scriptSig));
     else
         str += strprintf(", scriptSig=%s", HexStr(scriptSig).substr(0, 24));
-    if (nSequence != std::numeric_limits<unsigned int>::max())
+    if (nSequence != SEQUENCE_FINAL)
         str += strprintf(", nSequence=%u", nSequence);
     str += ")";
     return str;
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index c5d8a64a6d..1dca378b52 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -61,13 +61,40 @@ public:
     CScript scriptSig;
     uint32_t nSequence;
 
+    /* Setting nSequence to this value for every input in a transaction
+     * disables nLockTime. */
+    static const uint32_t SEQUENCE_FINAL = 0xffffffff;
+
+    /* Below flags apply in the context of BIP 68*/
+    /* If this flag set, CTxIn::nSequence is NOT interpreted as a
+     * relative lock-time. */
+    static const uint32_t SEQUENCE_LOCKTIME_DISABLE_FLAG = (1 << 31);
+
+    /* If CTxIn::nSequence encodes a relative lock-time and this flag
+     * is set, the relative lock-time has units of 512 seconds,
+     * otherwise it specifies blocks with a granularity of 1. */
+    static const uint32_t SEQUENCE_LOCKTIME_TYPE_FLAG = (1 << 22);
+
+    /* If CTxIn::nSequence encodes a relative lock-time, this mask is
+     * applied to extract that lock-time from the sequence field. */
+    static const uint32_t SEQUENCE_LOCKTIME_MASK = 0x0000ffff;
+
+    /* In order to use the same number of bits to encode roughly the
+     * same wall-clock duration, and because blocks are naturally
+     * limited to occur every 600s on average, the minimum granularity
+     * for time-based relative lock-time is fixed at 512 seconds.
+     * Converting from CTxIn::nSequence to seconds is performed by
+     * multiplying by 512 = 2^9, or equivalently shifting up by
+     * 9 bits. */
+    static const int SEQUENCE_LOCKTIME_GRANULARITY = 9;
+
     CTxIn()
     {
-        nSequence = std::numeric_limits<unsigned int>::max();
+        nSequence = SEQUENCE_FINAL;
     }
 
-    explicit CTxIn(COutPoint prevoutIn, CScript scriptSigIn=CScript(), uint32_t nSequenceIn=std::numeric_limits<unsigned int>::max());
-    CTxIn(uint256 hashPrevTx, uint32_t nOut, CScript scriptSigIn=CScript(), uint32_t nSequenceIn=std::numeric_limits<uint32_t>::max());
+    explicit CTxIn(COutPoint prevoutIn, CScript scriptSigIn=CScript(), uint32_t nSequenceIn=SEQUENCE_FINAL);
+    CTxIn(uint256 hashPrevTx, uint32_t nOut, CScript scriptSigIn=CScript(), uint32_t nSequenceIn=SEQUENCE_FINAL);
 
     ADD_SERIALIZE_METHODS;
 
@@ -78,11 +105,6 @@ public:
         READWRITE(nSequence);
     }
 
-    bool IsFinal() const
-    {
-        return (nSequence == std::numeric_limits<uint32_t>::max());
-    }
-
     friend bool operator==(const CTxIn& a, const CTxIn& b)
     {
         return (a.prevout   == b.prevout &&