go: add utils module

go/utils/README.md

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+# utils
+
+This package is meant to hold utilities used by
+[Optimistic Ethereum](https://github.com/ethereum-optimism/optimism) written in
+Golang.
+
+## Packages
+
+### Fees
+
+Package fees includes helpers for dealing with fees on Optimistic Ethereum
+
+#### `EncodeTxGasLimit(data []byte, l1GasPrice, l2GasLimit, l2GasPrice *big.Int) *big.Int`
+
+Encodes `tx.gasLimit` based on the variables that are used to determine it.
+
+#### `DecodeL2GasLimit(gasLimit *big.Int) *big.Int`
+
+Accepts the return value of `eth_estimateGas` and decodes the L2 gas limit that
+is encoded in the return value. This is the gas limit that is passed to the user
+contract within the OVM.

go/utils/fees/rollup_fee.go

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+package fees
+
+import (
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+// overhead represents the fixed cost of batch submission of a single
+// transaction in gas.
+const overhead uint64 = 4200 + 200*params.TxDataNonZeroGasEIP2028
+
+// feeScalar is used to scale the calculations in EncodeL2GasLimit
+// to prevent them from being too large
+const feeScalar uint64 = 10_000_000
+
+// TxGasPrice is a constant that determines the result of `eth_gasPrice`
+// It is scaled upwards by 50%
+// tx.gasPrice is hard coded to 1500 * wei and all transactions must set that
+// gas price.
+const TxGasPrice uint64 = feeScalar + (feeScalar / 2)
+
+// BigTxGasPrice is the L2GasPrice as type big.Int
+var BigTxGasPrice = new(big.Int).SetUint64(TxGasPrice)
+var bigFeeScalar = new(big.Int).SetUint64(feeScalar)
+
+const tenThousand = 10000
+
+var BigTenThousand = new(big.Int).SetUint64(tenThousand)
+
+// EncodeTxGasLimit computes the `tx.gasLimit` based on the L1/L2 gas prices and
+// the L2 gas limit. The L2 gas limit is encoded inside of the lower order bits
+// of the number like so: [          | l2GasLimit ]
+//                        [      tx.gaslimit      ]
+// The lower order bits must be large enough to fit the L2 gas limit, so 10**8
+// is chosen. If higher order bits collide with any bits from the L2 gas limit,
+// the L2 gas limit will not be able to be decoded.
+// An explicit design goal of this scheme was to make the L2 gas limit be human
+// readable. The entire number is interpreted as the gas limit when computing
+// the fee, so increasing the L2 Gas limit will increase the fee paid.
+// The calculation is:
+// l1GasLimit = zero_count(data) * 4 + non_zero_count(data) * 16 + overhead
+// roundedL2GasLimit = ceilmod(l2GasLimit, 10_000)
+// l1Fee = l1GasPrice * l1GasLimit
+// l2Fee = l2GasPrice * roundedL2GasLimit
+// sum = l1Fee + l2Fee
+// scaled = sum / scalar
+// rounded = ceilmod(scaled, tenThousand)
+// roundedScaledL2GasLimit = roundedL2GasLimit / tenThousand
+// result = rounded + roundedScaledL2GasLimit
+// Note that for simplicity purposes, only the calldata is passed into this
+// function when in reality the RLP encoded transaction should be. The
+// additional cost is added to the overhead constant to prevent the need to RLP
+// encode transactions during calls to `eth_estimateGas`
+func EncodeTxGasLimit(data []byte, l1GasPrice, l2GasLimit, l2GasPrice *big.Int) *big.Int {
+	l1GasLimit := calculateL1GasLimit(data, overhead)
+	roundedL2GasLimit := Ceilmod(l2GasLimit, BigTenThousand)
+	l1Fee := new(big.Int).Mul(l1GasPrice, l1GasLimit)
+	l2Fee := new(big.Int).Mul(l2GasPrice, roundedL2GasLimit)
+	sum := new(big.Int).Add(l1Fee, l2Fee)
+	scaled := new(big.Int).Div(sum, bigFeeScalar)
+	rounded := Ceilmod(scaled, BigTenThousand)
+	roundedScaledL2GasLimit := new(big.Int).Div(roundedL2GasLimit, BigTenThousand)
+	result := new(big.Int).Add(rounded, roundedScaledL2GasLimit)
+	return result
+}
+
+func Ceilmod(a, b *big.Int) *big.Int {
+	remainder := new(big.Int).Mod(a, b)
+	if remainder.Cmp(common.Big0) == 0 {
+		return a
+	}
+	sum := new(big.Int).Add(a, b)
+	rounded := new(big.Int).Sub(sum, remainder)
+	return rounded
+}
+
+// DecodeL2GasLimit decodes the L2 gas limit from an encoded L2 gas limit
+func DecodeL2GasLimit(gasLimit *big.Int) *big.Int {
+	scaled := new(big.Int).Mod(gasLimit, BigTenThousand)
+	return new(big.Int).Mul(scaled, BigTenThousand)
+}
+
+func DecodeL2GasLimitU64(gasLimit uint64) uint64 {
+	scaled := gasLimit % tenThousand
+	return scaled * tenThousand
+}
+
+// calculateL1GasLimit computes the L1 gasLimit based on the calldata and
+// constant sized overhead. The overhead can be decreased as the cost of the
+// batch submission goes down via contract optimizations. This will not overflow
+// under standard network conditions.
+func calculateL1GasLimit(data []byte, overhead uint64) *big.Int {
+	zeroes, ones := zeroesAndOnes(data)
+	zeroesCost := zeroes * params.TxDataZeroGas
+	onesCost := ones * params.TxDataNonZeroGasEIP2028
+	gasLimit := zeroesCost + onesCost + overhead
+	return new(big.Int).SetUint64(gasLimit)
+}
+
+func zeroesAndOnes(data []byte) (uint64, uint64) {
+	var zeroes uint64
+	var ones uint64
+	for _, byt := range data {
+		if byt == 0 {
+			zeroes++
+		} else {
+			ones++
+		}
+	}
+	return zeroes, ones
+}

go/utils/fees/rollup_fee_test.go

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+package fees
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/params"
+)
+
+var l1GasLimitTests = map[string]struct {
+	data     []byte
+	overhead uint64
+	expect   *big.Int
+}{
+	"simple":          {[]byte{}, 0, big.NewInt(0)},
+	"simple-overhead": {[]byte{}, 10, big.NewInt(10)},
+	"zeros":           {[]byte{0x00, 0x00, 0x00, 0x00}, 10, big.NewInt(26)},
+	"ones":            {[]byte{0x01, 0x02, 0x03, 0x04}, 200, big.NewInt(16*4 + 200)},
+}
+
+func TestL1GasLimit(t *testing.T) {
+	for name, tt := range l1GasLimitTests {
+		t.Run(name, func(t *testing.T) {
+			got := calculateL1GasLimit(tt.data, tt.overhead)
+			if got.Cmp(tt.expect) != 0 {
+				t.Fatal("Calculated gas limit does not match")
+			}
+		})
+	}
+}
+
+var feeTests = map[string]struct {
+	dataLen    int
+	l1GasPrice uint64
+	l2GasLimit uint64
+	l2GasPrice uint64
+}{
+	"simple": {
+		dataLen:    10,
+		l1GasPrice: params.GWei,
+		l2GasLimit: 437118,
+		l2GasPrice: params.GWei,
+	},
+	"zero-l2-gasprice": {
+		dataLen:    10,
+		l1GasPrice: params.GWei,
+		l2GasLimit: 196205,
+		l2GasPrice: 0,
+	},
+	"one-l2-gasprice": {
+		dataLen:    10,
+		l1GasPrice: params.GWei,
+		l2GasLimit: 196205,
+		l2GasPrice: 1,
+	},
+	"zero-l1-gasprice": {
+		dataLen:    10,
+		l1GasPrice: 0,
+		l2GasLimit: 196205,
+		l2GasPrice: params.GWei,
+	},
+	"one-l1-gasprice": {
+		dataLen:    10,
+		l1GasPrice: 1,
+		l2GasLimit: 23255,
+		l2GasPrice: params.GWei,
+	},
+	"zero-gasprices": {
+		dataLen:    10,
+		l1GasPrice: 0,
+		l2GasLimit: 23255,
+		l2GasPrice: 0,
+	},
+	"max-gaslimit": {
+		dataLen:    10,
+		l1GasPrice: params.GWei,
+		l2GasLimit: 99_970_000,
+		l2GasPrice: params.GWei,
+	},
+	"larger-divisor": {
+		dataLen:    10,
+		l1GasPrice: 0,
+		l2GasLimit: 10,
+		l2GasPrice: 0,
+	},
+}
+
+func TestCalculateRollupFee(t *testing.T) {
+	for name, tt := range feeTests {
+		t.Run(name, func(t *testing.T) {
+			data := make([]byte, tt.dataLen)
+			l1GasPrice := new(big.Int).SetUint64(tt.l1GasPrice)
+			l2GasLimit := new(big.Int).SetUint64(tt.l2GasLimit)
+			l2GasPrice := new(big.Int).SetUint64(tt.l2GasPrice)
+
+			fee := EncodeTxGasLimit(data, l1GasPrice, l2GasLimit, l2GasPrice)
+			decodedGasLimit := DecodeL2GasLimit(fee)
+			roundedL2GasLimit := Ceilmod(l2GasLimit, BigTenThousand)
+			if roundedL2GasLimit.Cmp(decodedGasLimit) != 0 {
+				t.Errorf("rollup fee check failed: expected %d, got %d", l2GasLimit.Uint64(), decodedGasLimit)
+			}
+		})
+	}
+}

go/utils/go.mod

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+module github.com/ethereum-optimism/optimism/go/utils
+
+go 1.15
+
+require github.com/ethereum/go-ethereum v1.9.10