From db1e8b805b04d75f20688a1aeeb838d011f5f6dc Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Thu, 5 Aug 2021 09:41:33 +0200
Subject: [PATCH] Calculate hashes only once

---
 abc/acks.nim         | 51 ++++++++++++++++++++++++++------------------
 abc/transactions.nim | 33 +++++++++++++++++-----------
 2 files changed, 50 insertions(+), 34 deletions(-)

diff --git a/abc/acks.nim b/abc/acks.nim
index bfcae88..7a3da69 100644
--- a/abc/acks.nim
+++ b/abc/acks.nim
@@ -10,11 +10,24 @@ type
     previous: ?Hash
     transactions: seq[Hash]
     validator: PublicKey
+    hash: Hash
     signature: ?Signature
 
-func init*(_: type Ack,
-           transactions: openArray[Hash],
-           validator: PublicKey): ?Ack =
+func toBytes*(ack: Ack): seq[byte] =
+  let previous = ack.previous |? Hash.default
+  result.add(previous.toBytes)
+  result.add(ack.transactions.len.uint8)
+  for transaction in ack.transactions:
+    result.add(transaction.toBytes)
+  result.add(ack.validator.toBytes)
+
+func init(_: type Ack,
+          previous: ?Hash,
+          transactions: openArray[Hash],
+          validator: PublicKey): ?Ack =
+  if previous =? previous and previous.kind != HashKind.Ack:
+    return none Ack
+
   if transactions.len == 0:
     return none Ack
 
@@ -22,20 +35,24 @@ func init*(_: type Ack,
     if transaction.kind != HashKind.Tx:
       return none Ack
 
-  some Ack(transactions: @transactions, validator: validator)
+  var ack = Ack(
+    previous: previous,
+    transactions: @transactions,
+    validator: validator
+  )
+  ack.hash = hash(ack.toBytes, HashKind.Ack)
+  some ack
+
+func init*(_: type Ack,
+           transactions: openArray[Hash],
+           validator: PublicKey): ?Ack =
+  Ack.init(Hash.none, transactions, validator)
 
 func init*(_: type Ack,
            previous: Hash,
            transactions: openArray[Hash],
            validator: PublicKey): ?Ack =
-  if previous.kind != HashKind.Ack:
-    return none Ack
-
-  without var ack =? Ack.init(transactions, validator):
-    return none Ack
-
-  ack.previous = previous.some
-  some ack
+  Ack.init(previous.some, transactions, validator)
 
 func previous*(ack: Ack): ?Hash =
   ack.previous
@@ -52,16 +69,8 @@ func signature*(ack: Ack): ?Signature =
 func `signature=`*(ack: var Ack, signature: Signature) =
   ack.signature = signature.some
 
-func toBytes*(ack: Ack): seq[byte] =
-  let previous = ack.previous |? Hash.default
-  result.add(previous.toBytes)
-  result.add(ack.transactions.len.uint8)
-  for transaction in ack.transactions:
-    result.add(transaction.toBytes)
-  result.add(ack.validator.toBytes)
-
 func hash*(ack: Ack): Hash =
-  hash(ack.toBytes, HashKind.Ack)
+  ack.hash
 
 func sign*(key: PrivateKey, ack: var Ack) =
   ack.signature = key.sign(ack.hash.toBytes).some
diff --git a/abc/transactions.nim b/abc/transactions.nim
index 2335596..ff8aec7 100644
--- a/abc/transactions.nim
+++ b/abc/transactions.nim
@@ -16,6 +16,7 @@ type
     inputs: seq[TxInput]
     outputs: seq[TxOutput]
     validator: PublicKey
+    hash: Hash
     signature: Signature
   TxInput* = tuple
     transaction: Hash
@@ -24,6 +25,17 @@ type
     owner: PublicKey
     value: UInt256
 
+func toBytes*(transaction: Transaction): seq[byte] =
+  result.add(transaction.inputs.len.uint8)
+  for (txHash, owner) in transaction.inputs:
+    result.add(txHash.toBytes)
+    result.add(owner.toBytes)
+  result.add(transaction.outputs.len.uint8)
+  for (owner, value) in transaction.outputs:
+    result.add(owner.toBytes)
+    result.add(value.toBytes)
+  result.add(transaction.validator.toBytes)
+
 func init*(_: type Transaction,
            inputs: openArray[TxInput],
            outputs: openArray[TxOutput],
@@ -38,7 +50,13 @@ func init*(_: type Transaction,
     if input.transaction.kind != HashKind.Tx:
       return none Transaction
 
-  some Transaction(inputs: @inputs, outputs: @outputs, validator: validator)
+  var transaction = Transaction(
+    inputs: @inputs,
+    outputs: @outputs,
+    validator: validator
+  )
+  transaction.hash = hash(transaction.toBytes, HashKind.Tx)
+  some transaction
 
 func init*(_: type Transaction,
            outputs: openArray[TxOutput],
@@ -60,19 +78,8 @@ func validator*(transaction: Transaction): PublicKey =
 func add*(transaction: var Transaction, signature: Signature) =
   transaction.signature = aggregate(transaction.signature, signature)
 
-func toBytes*(transaction: Transaction): seq[byte] =
-  result.add(transaction.inputs.len.uint8)
-  for (txHash, owner) in transaction.inputs:
-    result.add(txHash.toBytes)
-    result.add(owner.toBytes)
-  result.add(transaction.outputs.len.uint8)
-  for (owner, value) in transaction.outputs:
-    result.add(owner.toBytes)
-    result.add(value.toBytes)
-  result.add(transaction.validator.toBytes)
-
 func hash*(transaction: Transaction): Hash =
-  hash(transaction.toBytes, HashKind.Tx)
+  transaction.hash
 
 func sign*(key: PrivateKey, transaction: var Transaction) =
   transaction.add(key.sign(transaction.hash.toBytes))