all: replace division with right shift if possible (#29911)

Author: gitglorythegreat

cmd/evm/internal/t8ntool/execution.go

@@ -325,7 +325,7 @@ func (pre *Prestate) Apply(vmConfig vm.Config, chainConfig *params.ChainConfig,
 		var (
 			blockReward = big.NewInt(miningReward)
 			minerReward = new(big.Int).Set(blockReward)
-			perOmmer    = new(big.Int).Div(blockReward, big.NewInt(32))
+			perOmmer    = new(big.Int).Rsh(blockReward, 5)
 		)
 		for _, ommer := range pre.Env.Ommers {
 			// Add 1/32th for each ommer included
@@ -334,7 +334,7 @@ func (pre *Prestate) Apply(vmConfig vm.Config, chainConfig *params.ChainConfig,
 			reward := big.NewInt(8)
 			reward.Sub(reward, new(big.Int).SetUint64(ommer.Delta))
 			reward.Mul(reward, blockReward)
-			reward.Div(reward, big.NewInt(8))
+			reward.Rsh(reward, 3)
 			statedb.AddBalance(ommer.Address, uint256.MustFromBig(reward), tracing.BalanceIncreaseRewardMineUncle)
 		}
 		statedb.AddBalance(pre.Env.Coinbase, uint256.MustFromBig(minerReward), tracing.BalanceIncreaseRewardMineBlock)

consensus/ethash/consensus.go

@@ -562,12 +562,6 @@ func (ethash *Ethash) SealHash(header *types.Header) (hash common.Hash) {
 	return hash
 }
 
-// Some weird constants to avoid constant memory allocs for them.
-var (
-	u256_8  = uint256.NewInt(8)
-	u256_32 = uint256.NewInt(32)
-)
-
 // accumulateRewards credits the coinbase of the given block with the mining
 // reward. The total reward consists of the static block reward and rewards for
 // included uncles. The coinbase of each uncle block is also rewarded.
@@ -589,10 +583,10 @@ func accumulateRewards(config *params.ChainConfig, stateDB *state.StateDB, heade
 		r.AddUint64(uNum, 8)
 		r.Sub(r, hNum)
 		r.Mul(r, blockReward)
-		r.Div(r, u256_8)
+		r.Rsh(r, 3)
 		stateDB.AddBalance(uncle.Coinbase, r, tracing.BalanceIncreaseRewardMineUncle)
 
-		r.Div(blockReward, u256_32)
+		r.Rsh(blockReward, 5)
 		reward.Add(reward, r)
 	}
 	stateDB.AddBalance(header.Coinbase, reward, tracing.BalanceIncreaseRewardMineBlock)

core/types/transaction_signing.go

@@ -572,6 +572,6 @@ func deriveChainId(v *big.Int) *big.Int {
 		}
 		return new(big.Int).SetUint64((v - 35) / 2)
 	}
-	v = new(big.Int).Sub(v, big.NewInt(35))
-	return v.Div(v, big.NewInt(2))
+	v.Sub(v, big.NewInt(35))
+	return v.Rsh(v, 1)
 }

core/vm/contracts.go

@@ -296,10 +296,7 @@ type bigModExp struct {
 var (
 	big1      = big.NewInt(1)
 	big3      = big.NewInt(3)
-	big4      = big.NewInt(4)
 	big7      = big.NewInt(7)
-	big8      = big.NewInt(8)
-	big16     = big.NewInt(16)
 	big20     = big.NewInt(20)
 	big32     = big.NewInt(32)
 	big64     = big.NewInt(64)
@@ -325,13 +322,13 @@ func modexpMultComplexity(x *big.Int) *big.Int {
 	case x.Cmp(big1024) <= 0:
 		// (x ** 2 // 4 ) + ( 96 * x - 3072)
 		x = new(big.Int).Add(
-			new(big.Int).Div(new(big.Int).Mul(x, x), big4),
+			new(big.Int).Rsh(new(big.Int).Mul(x, x), 2),
 			new(big.Int).Sub(new(big.Int).Mul(big96, x), big3072),
 		)
 	default:
 		// (x ** 2 // 16) + (480 * x - 199680)
 		x = new(big.Int).Add(
-			new(big.Int).Div(new(big.Int).Mul(x, x), big16),
+			new(big.Int).Rsh(new(big.Int).Mul(x, x), 4),
 			new(big.Int).Sub(new(big.Int).Mul(big480, x), big199680),
 		)
 	}
@@ -369,7 +366,7 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
 	adjExpLen := new(big.Int)
 	if expLen.Cmp(big32) > 0 {
 		adjExpLen.Sub(expLen, big32)
-		adjExpLen.Mul(big8, adjExpLen)
+		adjExpLen.Lsh(adjExpLen, 3)
 	}
 	adjExpLen.Add(adjExpLen, big.NewInt(int64(msb)))
 	// Calculate the gas cost of the operation
@@ -383,8 +380,8 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
 		//    ceiling(x/8)^2
 		//
 		//where is x is max(length_of_MODULUS, length_of_BASE)
-		gas = gas.Add(gas, big7)
-		gas = gas.Div(gas, big8)
+		gas.Add(gas, big7)
+		gas.Rsh(gas, 3)
 		gas.Mul(gas, gas)
 
 		gas.Mul(gas, math.BigMax(adjExpLen, big1))