improve readability by removing extra var (#1345)

* add regression test

* apply fix

* improve readability by removing extra var

* reorder equal params

consensus/dummy/dynamic_fees.go

@@ -70,26 +70,24 @@ func CalcBaseFee(config *params.ChainConfig, feeConfig commontype.FeeConfig, par
 		return newRollupWindow, baseFee, nil
 	}
 
+	num := new(big.Int)
+
 	if totalGas > parentGasTarget {
 		// If the parent block used more gas than its target, the baseFee should increase.
-		gasUsedDelta := new(big.Int).SetUint64(totalGas - parentGasTarget)
-		x := new(big.Int).Mul(parent.BaseFee, gasUsedDelta)
-		y := x.Div(x, parentGasTargetBig)
-		baseFeeDelta := math.BigMax(
-			x.Div(y, baseFeeChangeDenominator),
-			common.Big1,
-		)
+		num.SetUint64(totalGas - parentGasTarget)
+		num.Mul(num, parent.BaseFee)
+		num.Div(num, parentGasTargetBig)
+		num.Div(num, baseFeeChangeDenominator)
+		baseFeeDelta := math.BigMax(num, common.Big1)
 
 		baseFee.Add(baseFee, baseFeeDelta)
 	} else {
 		// Otherwise if the parent block used less gas than its target, the baseFee should decrease.
-		gasUsedDelta := new(big.Int).SetUint64(parentGasTarget - totalGas)
-		x := new(big.Int).Mul(parent.BaseFee, gasUsedDelta)
-		y := x.Div(x, parentGasTargetBig)
-		baseFeeDelta := math.BigMax(
-			x.Div(y, baseFeeChangeDenominator),
-			common.Big1,
-		)
+		num.SetUint64(parentGasTarget - totalGas)
+		num.Mul(num, parent.BaseFee)
+		num.Div(num, parentGasTargetBig)
+		num.Div(num, baseFeeChangeDenominator)
+		baseFeeDelta := math.BigMax(num, common.Big1)
 
 		// If [roll] is greater than [rollupWindow], apply the state transition to the base fee to account
 		// for the interval during which no blocks were produced.