Add dynafed helper functions

src/Makefile.am

@@ -134,6 +134,7 @@ BITCOIN_CORE_H = \
   core_io.h \
   core_memusage.h \
   cuckoocache.h \
+  dynafed.h \
   fs.h \
   httprpc.h \
   httpserver.h \
@@ -401,10 +402,13 @@ libbitcoin_consensus_a_SOURCES = \
   arith_uint256.cpp \
   arith_uint256.h \
   asset.cpp \
+  chain.h \
+  chain.cpp \
   consensus/merkle.cpp \
   consensus/merkle.h \
   consensus/params.h \
   consensus/validation.h \
+  dynafed.cpp \
   hash.cpp \
   hash.h \
   prevector.h \
@@ -433,6 +437,8 @@ libbitcoin_consensus_a_SOURCES = \
   script/script.h \
   script/script_error.cpp \
   script/script_error.h \
+  script/standard.h \
+  script/standard.cpp \
   serialize.h \
   span.h \
   tinyformat.h \

src/chainparams.cpp

@@ -482,6 +482,9 @@ class CCustomParams : public CRegTestParams {
 
         consensus.nMinimumChainWork = uint256S(args.GetArg("-con_nminimumchainwork", "0x0"));
         consensus.defaultAssumeValid = uint256S(args.GetArg("-con_defaultassumevalid", "0x00"));
+        // TODO: pass in serialized vector of byte vectors, parse into extension space
+        // Junk keys for testing
+        consensus.first_extension_space = {ParseHex("02fcba7ecf41bc7e1be4ee122d9d22e3333671eb0a3a87b5cdf099d59874e1940f02fcba7ecf41bc7e1be4ee122d9d22e3333671eb0a3a87b5cdf099d59874e1940f")};
 
         nPruneAfterHeight = (uint64_t)args.GetArg("-npruneafterheight", nPruneAfterHeight);
         fDefaultConsistencyChecks = args.GetBoolArg("-fdefaultconsistencychecks", fDefaultConsistencyChecks);

src/consensus/params.h

@@ -99,6 +99,8 @@ struct Params {
     CScript signblockscript;
     uint32_t max_block_signature_size;
     // g_signed_blocks - Whether blocks are signed or not, get around circular dep
+    // Used to seed the extension space for first dynamic blocks
+    std::vector<std::vector<unsigned char>> first_extension_space;
 };
 } // namespace Consensus
 

src/dynafed.cpp

@@ -0,0 +1,97 @@
+
+#include <dynafed.h>
+#include <script/standard.h>
+
+bool NextBlockIsParameterTransition(const CBlockIndex* pindexPrev, const Consensus::Params& consensus, ConsensusParamEntry& winning_entry)
+{
+    uint32_t next_height = pindexPrev->nHeight + 1;
+    assert(consensus.dynamic_epoch_length != 0);
+    if (next_height % consensus.dynamic_epoch_length != 0) {
+        winning_entry.SetNull();
+        return false;
+    }
+    std::map<uint256, uint32_t> vote_tally;
+    assert(next_height >= consensus.dynamic_epoch_length);
+    for (int32_t height = next_height - 1; height >= (int32_t)(next_height - consensus.dynamic_epoch_length); --height) {
+        const CBlockIndex* p_epoch_walk = pindexPrev->GetAncestor(height);
+        assert(p_epoch_walk);
+        const ConsensusParamEntry& proposal = p_epoch_walk->d_params.m_proposed;
+        const uint256 proposal_root = proposal.CalculateRoot();
+        vote_tally[proposal_root]++;
+        // Short-circuit once 4/5 threshhold is reached
+        if (vote_tally[proposal_root] >=
+                (consensus.dynamic_epoch_length*4)/5) {
+            winning_entry = proposal;
+            return true;
+        }
+        // Also stop early if "no-vote" crosses 1/4
+        if (proposal_root.IsNull() &&
+                vote_tally[proposal_root] > consensus.dynamic_epoch_length/5) {
+            winning_entry.SetNull();
+            return false;
+        }
+    }
+    winning_entry.SetNull();
+    return false;
+}
+
+ConsensusParamEntry ComputeNextBlockFullCurrentParameters(const CBlockIndex* pindexPrev, const Consensus::Params& consensus)
+{
+    assert(pindexPrev);
+
+    uint32_t next_height = pindexPrev->nHeight+1;
+    const uint32_t epoch_length = consensus.dynamic_epoch_length;
+    uint32_t epoch_age = next_height % epoch_length;
+
+    ConsensusParamEntry winning_proposal;
+    // Early return when there is a winning proposal
+    if (NextBlockIsParameterTransition(pindexPrev, consensus, winning_proposal)) {
+        assert(epoch_age == 0);
+        return winning_proposal;
+    }
+
+    // Since no transition took place, find most recent epoch start
+
+    // If next block is start of new epoch, walk backwards one epoch
+    uint32_t epoch_start_height = next_height - epoch_age;
+    if (epoch_age == 0) {
+        epoch_start_height -= epoch_length;
+    }
+
+    // We need to put in place the previous epoch's current which
+    // may be pre-dynafed params
+    const CBlockIndex* p_epoch_start = pindexPrev->GetAncestor(epoch_start_height);
+    assert(p_epoch_start);
+    if (p_epoch_start->d_params.IsNull()) {
+        // We need to construct the "full" current parameters of pre-dynafed
+        // consensus
+
+        // Convert signblockscript to P2WSH
+        CScript p2wsh_signblock_script = GetScriptForDestination(WitnessV0ScriptHash(p_epoch_start->proof.challenge));
+        winning_proposal = ConsensusParamEntry(p2wsh_signblock_script, consensus.max_block_signature_size+consensus.signblockscript.size(), consensus.fedpegScript, consensus.first_extension_space);
+    } else {
+        winning_proposal = p_epoch_start->d_params.m_current;
+    }
+    return winning_proposal;
+}
+
+// TODO cache this in CBlockIndex itself?
+ConsensusParamEntry ComputeNextBlockCurrentParameters(const CBlockIndex* pindexPrev, const Consensus::Params& consensus)
+{
+    assert(pindexPrev);
+
+    ConsensusParamEntry entry = ComputeNextBlockFullCurrentParameters(pindexPrev, consensus);
+
+    uint32_t next_height = pindexPrev->nHeight+1;
+    const uint32_t epoch_length = consensus.dynamic_epoch_length;
+    uint32_t epoch_age = next_height % epoch_length;
+
+    // Return appropriate format based on epoch age
+    if (epoch_age > 0) {
+        // TODO implement "prune" function to remove fields in place and change serialize type
+        return ConsensusParamEntry(entry.m_signblockscript, entry.m_sbs_wit_limit);
+    } else {
+        return entry;
+    }
+}
+

src/dynafed.h

@@ -0,0 +1,19 @@
+
+#ifndef BITCOIN_DYNAFED_H
+#define BITCOIN_DYNAFED_H
+
+#include <chain.h>
+#include <chainparams.h>
+#include <primitives/block.h>
+
+
+bool NextBlockIsParameterTransition(const CBlockIndex* pindexPrev, const Consensus::Params& consensus, ConsensusParamEntry& winning_entry);
+
+/* Compute the next block's enforced parameters */
+ConsensusParamEntry ComputeNextBlockFullCurrentParameters(const CBlockIndex* pindexPrev, const Consensus::Params& consensus);
+/* Compute the next block's expected published parameters. Blocks at "epoch_age" of non-0 only
+ * publish signblockscript-related fields */
+ConsensusParamEntry ComputeNextBlockCurrentParameters(const CBlockIndex* pindexPrev, const Consensus::Params& consensus);
+
+
+#endif //  BITCOIN_DYNAFED_H