Release v0.1.0

vendor/github.com/btcsuite/btcd/blockchain/weight.go

@@ -0,0 +1,117 @@
+// Copyright (c) 2013-2017 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package blockchain
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
+)
+
+const (
+	// MaxBlockWeight defines the maximum block weight, where "block
+	// weight" is interpreted as defined in BIP0141. A block's weight is
+	// calculated as the sum of the of bytes in the existing transactions
+	// and header, plus the weight of each byte within a transaction. The
+	// weight of a "base" byte is 4, while the weight of a witness byte is
+	// 1. As a result, for a block to be valid, the BlockWeight MUST be
+	// less than, or equal to MaxBlockWeight.
+	MaxBlockWeight = 4000000
+
+	// MaxBlockBaseSize is the maximum number of bytes within a block
+	// which can be allocated to non-witness data.
+	MaxBlockBaseSize = 1000000
+
+	// MaxBlockSigOpsCost is the maximum number of signature operations
+	// allowed for a block. It is calculated via a weighted algorithm which
+	// weights segregated witness sig ops lower than regular sig ops.
+	MaxBlockSigOpsCost = 80000
+
+	// WitnessScaleFactor determines the level of "discount" witness data
+	// receives compared to "base" data. A scale factor of 4, denotes that
+	// witness data is 1/4 as cheap as regular non-witness data.
+	WitnessScaleFactor = 4
+
+	// MinTxOutputWeight is the minimum possible weight for a transaction
+	// output.
+	MinTxOutputWeight = WitnessScaleFactor * wire.MinTxOutPayload
+
+	// MaxOutputsPerBlock is the maximum number of transaction outputs there
+	// can be in a block of max weight size.
+	MaxOutputsPerBlock = MaxBlockWeight / MinTxOutputWeight
+)
+
+// GetBlockWeight computes the value of the weight metric for a given block.
+// Currently the weight metric is simply the sum of the block's serialized size
+// without any witness data scaled proportionally by the WitnessScaleFactor,
+// and the block's serialized size including any witness data.
+func GetBlockWeight(blk *btcutil.Block) int64 {
+	msgBlock := blk.MsgBlock()
+
+	baseSize := msgBlock.SerializeSizeStripped()
+	totalSize := msgBlock.SerializeSize()
+
+	// (baseSize * 3) + totalSize
+	return int64((baseSize * (WitnessScaleFactor - 1)) + totalSize)
+}
+
+// GetTransactionWeight computes the value of the weight metric for a given
+// transaction. Currently the weight metric is simply the sum of the
+// transactions's serialized size without any witness data scaled
+// proportionally by the WitnessScaleFactor, and the transaction's serialized
+// size including any witness data.
+func GetTransactionWeight(tx *btcutil.Tx) int64 {
+	msgTx := tx.MsgTx()
+
+	baseSize := msgTx.SerializeSizeStripped()
+	totalSize := msgTx.SerializeSize()
+
+	// (baseSize * 3) + totalSize
+	return int64((baseSize * (WitnessScaleFactor - 1)) + totalSize)
+}
+
+// GetSigOpCost returns the unified sig op cost for the passed transaction
+// respecting current active soft-forks which modified sig op cost counting.
+// The unified sig op cost for a transaction is computed as the sum of: the
+// legacy sig op count scaled according to the WitnessScaleFactor, the sig op
+// count for all p2sh inputs scaled by the WitnessScaleFactor, and finally the
+// unscaled sig op count for any inputs spending witness programs.
+func GetSigOpCost(tx *btcutil.Tx, isCoinBaseTx bool, utxoView *UtxoViewpoint, bip16, segWit bool) (int, error) {
+	numSigOps := CountSigOps(tx) * WitnessScaleFactor
+	if bip16 {
+		numP2SHSigOps, err := CountP2SHSigOps(tx, isCoinBaseTx, utxoView)
+		if err != nil {
+			return 0, nil
+		}
+		numSigOps += (numP2SHSigOps * WitnessScaleFactor)
+	}
+
+	if segWit && !isCoinBaseTx {
+		msgTx := tx.MsgTx()
+		for txInIndex, txIn := range msgTx.TxIn {
+			// Ensure the referenced output is available and hasn't
+			// already been spent.
+			utxo := utxoView.LookupEntry(txIn.PreviousOutPoint)
+			if utxo == nil || utxo.IsSpent() {
+				str := fmt.Sprintf("output %v referenced from "+
+					"transaction %s:%d either does not "+
+					"exist or has already been spent",
+					txIn.PreviousOutPoint, tx.Hash(),
+					txInIndex)
+				return 0, ruleError(ErrMissingTxOut, str)
+			}
+
+			witness := txIn.Witness
+			sigScript := txIn.SignatureScript
+			pkScript := utxo.PkScript()
+			numSigOps += txscript.GetWitnessSigOpCount(sigScript, pkScript, witness)
+		}
+
+	}
+
+	return numSigOps, nil
+}