Implement ZIP 317 computations.

Signed-off-by: Daira Emma Hopwood <daira@jacaranda.org>

src/Makefile.am

@@ -535,6 +535,7 @@ libbitcoin_common_a_SOURCES = \
   transaction_builder.cpp \
   util/test.cpp \
   warnings.cpp \
+  zip317.cpp \
   $(BITCOIN_CORE_H) \
   $(LIBZCASH_H)
 
@@ -699,7 +700,8 @@ libzcash_script_la_SOURCES = \
   script/interpreter.cpp \
   script/script.cpp \
   uint256.cpp \
-  util/strencodings.cpp
+  util/strencodings.cpp \
+  zip317.cpp
 
 if GLIBC_BACK_COMPAT
   libzcash_script_la_SOURCES += compat/glibc_compat.cpp

src/primitives/transaction.cpp

@@ -9,6 +9,7 @@
 #include "hash.h"
 #include "tinyformat.h"
 #include "util/strencodings.h"
+#include "zip317.h"
 
 #include <rust/transaction.h>
 
@@ -385,6 +386,20 @@ unsigned int CTransaction::CalculateModifiedSize(unsigned int nTxSize) const
     return nTxSize;
 }
 
+CAmount CTransaction::GetConventionalFee() const {
+    return CalculateConventionalFee(GetLogicalActionCount());
+}
+
+size_t CTransaction::GetLogicalActionCount() const {
+    return CalculateLogicalActionCount(
+            vin,
+            vout,
+            vJoinSplit.size(),
+            vShieldedSpend.size(),
+            vShieldedOutput.size(),
+            orchardBundle.GetNumActions());
+}
+
 std::string CTransaction::ToString() const
 {
     std::string str;

src/primitives/transaction.h

@@ -977,6 +977,14 @@ public:
     // Compute modified tx size for priority calculation (optionally given tx size)
     unsigned int CalculateModifiedSize(unsigned int nTxSize=0) const;
 
+    // Return the conventional fee for this transaction calculated according to
+    // <https://zips.z.cash/zip-0317#fee-calculation>.
+    CAmount GetConventionalFee() const;
+
+    // Return the number of logical actions calculated according to
+    // <https://zips.z.cash/zip-0317#fee-calculation>.
+    size_t GetLogicalActionCount() const;
+
     bool IsCoinBase() const
     {
         return (vin.size() == 1 && vin[0].prevout.IsNull());

src/zip317.cpp

@@ -0,0 +1,32 @@
+// Copyright (c) 2023-2023 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://www.opensource.org/licenses/mit-license.php .
+
+#include "zip317.h"
+
+#include <algorithm>
+
+static size_t ceil_div(size_t num, size_t den) {
+    return (num + den - 1)/den;
+}
+
+CAmount CalculateConventionalFee(size_t logicalActionCount) {
+    return MARGINAL_FEE * std::max(GRACE_ACTIONS, logicalActionCount);
+}
+
+size_t CalculateLogicalActionCount(
+        const std::vector<CTxIn>& vin,
+        const std::vector<CTxOut>& vout,
+        unsigned int joinSplitCount,
+        unsigned int saplingSpendCount,
+        unsigned int saplingOutputCount,
+        unsigned int orchardActionCount) {
+    const size_t tx_in_total_size = GetSerializeSize(vin, SER_NETWORK, PROTOCOL_VERSION);
+    const size_t tx_out_total_size = GetSerializeSize(vout, SER_NETWORK, PROTOCOL_VERSION);
+
+    return std::max(ceil_div(tx_in_total_size, P2PKH_STANDARD_INPUT_SIZE),
+                    ceil_div(tx_out_total_size, P2PKH_STANDARD_OUTPUT_SIZE)) +
+           2 * joinSplitCount +
+           std::max(saplingSpendCount, saplingOutputCount) +
+           orchardActionCount;
+}

src/zip317.h

@@ -0,0 +1,40 @@
+// Copyright (c) 2023-2023 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://www.opensource.org/licenses/mit-license.php .
+
+#ifndef ZCASH_ZIP317_H
+#define ZCASH_ZIP317_H
+
+#include "amount.h"
+#include "primitives/transaction.h"
+
+#include <cstdint>
+#include <cstddef>
+#include <vector>
+
+// Constants for fee calculation.
+static const CAmount MARGINAL_FEE = 5000;
+static const size_t GRACE_ACTIONS = 2;
+static const size_t P2PKH_STANDARD_INPUT_SIZE = 150;
+static const size_t P2PKH_STANDARD_OUTPUT_SIZE = 34;
+
+// Constants for block template construction.
+static const int64_t WEIGHT_RATIO_SCALE = INT64_C(10000000000000000);
+static const int64_t WEIGHT_RATIO_CAP = 4;
+static const size_t BLOCK_UNPAID_ACTION_LIMIT = 50;
+
+/// Return the conventional fee for the given `logicalActionCount` calculated according to
+/// <https://zips.z.cash/zip-0317#fee-calculation>.
+CAmount CalculateConventionalFee(size_t logicalActionCount);
+
+/// Return the number of logical actions calculated according to
+/// <https://zips.z.cash/zip-0317#fee-calculation>.
+size_t CalculateLogicalActionCount(
+        const std::vector<CTxIn>& vin,
+        const std::vector<CTxOut>& vout,
+        unsigned int joinSplitCount,
+        unsigned int saplingSpendCount,
+        unsigned int saplingOutputCount,
+        unsigned int orchardActionCount);
+
+#endif // ZCASH_ZIP317_H