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

consensus/misc/eip4844.go

@@ -22,13 +22,18 @@ import (
 	"github.com/ethereum/go-ethereum/params"
 )
 
+var (
+	expFactor      = big.NewInt(params.BlobTxMinDataGasprice)
+	expDenominator = 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(big.NewInt(params.BlobTxMinDataGasprice), excessDataGas, big.NewInt(params.BlobTxDataGaspriceUpdateFraction))
+	return fakeExponential(expFactor, excessDataGas, expDenominator)
 }
 
 // fakeExponential approximates factor * e ** (numerator / denominator) using

consensus/misc/eip4844_test.go

@@ -17,6 +17,7 @@
 package misc
 
 import (
+	"fmt"
 	"math/big"
 	"testing"
 
@@ -69,9 +70,15 @@ func TestFakeExponential(t *testing.T) {
 		{2, 5, 2, 23},   // approximate 24.36
 	}
 	for i, tt := range tests {
-		have := fakeExponential(big.NewInt(tt.factor), big.NewInt(tt.numerator), big.NewInt(tt.denominator))
+		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)
+		}
 	}
 }