consensus/misc, params: add EIP-4844 blobfee conversions (#27041)

* consensus/misc, params: add EIP-4844 blobfee conversions

* consensus/misc: pull in fakeExponential test cases

* consensus/misc: reuse bigints

* consensus/misc: nit renames, additional larger testcase

---------

Co-authored-by: Roberto Bayardo <bayardo@alum.mit.edu>
Co-authored-by: Martin Holst Swende <martin@swende.se>

consensus/misc/eip4844.go

@@ -0,0 +1,54 @@
+// Copyright 2023 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package misc
+
+import (
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/params"
+)
+
+var (
+	minDataGasPrice            = big.NewInt(params.BlobTxMinDataGasprice)
+	dataGaspriceUpdateFraction = big.NewInt(params.BlobTxDataGaspriceUpdateFraction)
+)
+
+// CalcBlobFee calculates the blobfee from the header's excess data gas field.
+func CalcBlobFee(excessDataGas *big.Int) *big.Int {
+	// If this block does not yet have EIP-4844 enabled, return the starting fee
+	if excessDataGas == nil {
+		return big.NewInt(params.BlobTxMinDataGasprice)
+	}
+	return fakeExponential(minDataGasPrice, excessDataGas, dataGaspriceUpdateFraction)
+}
+
+// fakeExponential approximates factor * e ** (numerator / denominator) using
+// Taylor expansion.
+func fakeExponential(factor, numerator, denominator *big.Int) *big.Int {
+	var (
+		output = new(big.Int)
+		accum  = new(big.Int).Mul(factor, denominator)
+	)
+	for i := 1; accum.Sign() > 0; i++ {
+		output.Add(output, accum)
+
+		accum.Mul(accum, numerator)
+		accum.Div(accum, denominator)
+		accum.Div(accum, big.NewInt(int64(i)))
+	}
+	return output.Div(output, denominator)
+}

consensus/misc/eip4844_test.go

@@ -0,0 +1,85 @@
+// Copyright 2023 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package misc
+
+import (
+	"fmt"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/params"
+)
+
+func TestCalcBlobFee(t *testing.T) {
+	tests := []struct {
+		excessDataGas int64
+		blobfee       int64
+	}{
+		{0, 1},
+		{1542706, 1},
+		{1542707, 2},
+		{10 * 1024 * 1024, 111},
+	}
+	have := CalcBlobFee(nil)
+	if have.Int64() != params.BlobTxMinDataGasprice {
+		t.Errorf("nil test: blobfee mismatch: have %v, want %v", have, params.BlobTxMinDataGasprice)
+	}
+	for i, tt := range tests {
+		have := CalcBlobFee(big.NewInt(tt.excessDataGas))
+		if have.Int64() != tt.blobfee {
+			t.Errorf("test %d: blobfee mismatch: have %v want %v", i, have, tt.blobfee)
+		}
+	}
+}
+
+func TestFakeExponential(t *testing.T) {
+	tests := []struct {
+		factor      int64
+		numerator   int64
+		denominator int64
+		want        int64
+	}{
+		// When numerator == 0 the return value should always equal the value of factor
+		{1, 0, 1, 1},
+		{38493, 0, 1000, 38493},
+		{0, 1234, 2345, 0}, // should be 0
+		{1, 2, 1, 6},       // approximate 7.389
+		{1, 4, 2, 6},
+		{1, 3, 1, 16}, // approximate 20.09
+		{1, 6, 2, 18},
+		{1, 4, 1, 49}, // approximate 54.60
+		{1, 8, 2, 50},
+		{10, 8, 2, 542}, // approximate 540.598
+		{11, 8, 2, 596}, // approximate 600.58
+		{1, 5, 1, 136},  // approximate 148.4
+		{1, 5, 2, 11},   // approximate 12.18
+		{2, 5, 2, 23},   // approximate 24.36
+		{1, 50000000, 2225652, 5709098764},
+	}
+	for i, tt := range tests {
+		f, n, d := big.NewInt(tt.factor), big.NewInt(tt.numerator), big.NewInt(tt.denominator)
+		original := fmt.Sprintf("%d %d %d", f, n, d)
+		have := fakeExponential(f, n, d)
+		if have.Int64() != tt.want {
+			t.Errorf("test %d: fake exponential mismatch: have %v want %v", i, have, tt.want)
+		}
+		later := fmt.Sprintf("%d %d %d", f, n, d)
+		if original != later {
+			t.Errorf("test %d: fake exponential modified arguments: have\n%v\nwant\n%v", i, later, original)
+		}
+	}
+}

params/protocol_params.go

@@ -159,6 +159,9 @@ const (
 	// up to half the consumed gas could be refunded. Redefined as 1/5th in EIP-3529
 	RefundQuotient        uint64 = 2
 	RefundQuotientEIP3529 uint64 = 5
+
+	BlobTxMinDataGasprice            = 1       // Minimum gas price for data blobs
+	BlobTxDataGaspriceUpdateFraction = 2225652 // Controls the maximum rate of change for data gas price
 )
 
 // Gas discount table for BLS12-381 G1 and G2 multi exponentiation operations