all: unify big.Int zero checks, use common/math in more places (#3716)

* common/math: optimize PaddedBigBytes, use it more

name              old time/op    new time/op    delta
PaddedBigBytes-8    71.1ns ± 5%    46.1ns ± 1%  -35.15%  (p=0.000 n=20+19)

name              old alloc/op   new alloc/op   delta
PaddedBigBytes-8     48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=20+20)

* all: unify big.Int zero checks

Various checks were in use. This commit replaces them all with Int.Sign,
which is cheaper and less code.

eg templates:

    func before(x *big.Int) bool { return x.BitLen() == 0 }
    func after(x *big.Int) bool  { return x.Sign() == 0 }

    func before(x *big.Int) bool { return x.BitLen() > 0 }
    func after(x *big.Int) bool  { return x.Sign() != 0 }

    func before(x *big.Int) int { return x.Cmp(common.Big0) }
    func after(x *big.Int) int  { return x.Sign() }

* common/math, crypto/secp256k1: make ReadBits public in package math

11 files changed, 27 insertions, 25 deletions

diff --git a/core/headerchain.go b/core/headerchain.go
index a0550a428..046275933 100644
--- a/core/headerchain.go
+++ b/core/headerchain.go
@@ -359,7 +359,7 @@ func (hc *HeaderChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []co
 			break
 		}
 		chain = append(chain, next)
-		if header.Number.Cmp(common.Big0) == 0 {
+		if header.Number.Sign() == 0 {
 			break
 		}
 	}
diff --git a/core/state/state_object.go b/core/state/state_object.go
index ebb103806..17726dd0c 100644
--- a/core/state/state_object.go
+++ b/core/state/state_object.go
@@ -93,7 +93,7 @@ type stateObject struct {
 
 // empty returns whether the account is considered empty.
 func (s *stateObject) empty() bool {
-	return s.data.Nonce == 0 && s.data.Balance.BitLen() == 0 && bytes.Equal(s.data.CodeHash, emptyCodeHash)
+	return s.data.Nonce == 0 && s.data.Balance.Sign() == 0 && bytes.Equal(s.data.CodeHash, emptyCodeHash)
 }
 
 // Account is the Ethereum consensus representation of accounts.
@@ -243,7 +243,7 @@ func (self *stateObject) CommitTrie(db trie.Database, dbw trie.DatabaseWriter) e
 func (c *stateObject) AddBalance(amount *big.Int) {
 	// EIP158: We must check emptiness for the objects such that the account
 	// clearing (0,0,0 objects) can take effect.
-	if amount.Cmp(common.Big0) == 0 {
+	if amount.Sign() == 0 {
 		if c.empty() {
 			c.touch()
 		}
@@ -260,7 +260,7 @@ func (c *stateObject) AddBalance(amount *big.Int) {
 // SubBalance removes amount from c's balance.
 // It is used to remove funds from the origin account of a transfer.
 func (c *stateObject) SubBalance(amount *big.Int) {
-	if amount.Cmp(common.Big0) == 0 {
+	if amount.Sign() == 0 {
 		return
 	}
 	c.SetBalance(new(big.Int).Sub(c.Balance(), amount))
diff --git a/core/tx_pool.go b/core/tx_pool.go
index b0a8eea0f..e8d93d20e 100644
--- a/core/tx_pool.go
+++ b/core/tx_pool.go
@@ -299,7 +299,7 @@ func (pool *TxPool) validateTx(tx *types.Transaction) error {
 	// Transactions can't be negative. This may never happen
 	// using RLP decoded transactions but may occur if you create
 	// a transaction using the RPC for example.
-	if tx.Value().Cmp(common.Big0) < 0 {
+	if tx.Value().Sign() < 0 {
 		return ErrNegativeValue
 	}
 
diff --git a/core/types/transaction.go b/core/types/transaction.go
index 9382acb70..ab0bba4dc 100644
--- a/core/types/transaction.go
+++ b/core/types/transaction.go
@@ -42,7 +42,7 @@ var (
 
 // deriveSigner makes a *best* guess about which signer to use.
 func deriveSigner(V *big.Int) Signer {
-	if V.BitLen() > 0 && isProtectedV(V) {
+	if V.Sign() != 0 && isProtectedV(V) {
 		return EIP155Signer{chainId: deriveChainId(V)}
 	} else {
 		return HomesteadSigner{}
diff --git a/core/types/transaction_signing.go b/core/types/transaction_signing.go
index 7d7b63e9f..e7eb7c5f0 100644
--- a/core/types/transaction_signing.go
+++ b/core/types/transaction_signing.go
@@ -167,7 +167,7 @@ func (s EIP155Signer) WithSignature(tx *Transaction, sig []byte) (*Transaction,
 	cpy.data.R = new(big.Int).SetBytes(sig[:32])
 	cpy.data.S = new(big.Int).SetBytes(sig[32:64])
 	cpy.data.V = new(big.Int).SetBytes([]byte{sig[64]})
-	if s.chainId.BitLen() > 0 {
+	if s.chainId.Sign() != 0 {
 		cpy.data.V = big.NewInt(int64(sig[64] + 35))
 		cpy.data.V.Add(cpy.data.V, s.chainIdMul)
 	}
diff --git a/core/types/transaction_signing_test.go b/core/types/transaction_signing_test.go
index 3216fcfad..7f799fb10 100644
--- a/core/types/transaction_signing_test.go
+++ b/core/types/transaction_signing_test.go
@@ -71,7 +71,7 @@ func TestEIP155ChainId(t *testing.T) {
 		t.Error("didn't expect tx to be protected")
 	}
 
-	if tx.ChainId().BitLen() > 0 {
+	if tx.ChainId().Sign() != 0 {
 		t.Error("expected chain id to be 0 got", tx.ChainId())
 	}
 }
diff --git a/core/vm/common.go b/core/vm/common.go
index ef40c4a95..779cee006 100644
--- a/core/vm/common.go
+++ b/core/vm/common.go
@@ -25,7 +25,7 @@ import (
 
 // calculates the memory size required for a step
 func calcMemSize(off, l *big.Int) *big.Int {
-	if l.Cmp(common.Big0) == 0 {
+	if l.Sign() == 0 {
 		return common.Big0
 	}
 
diff --git a/core/vm/evm.go b/core/vm/evm.go
index d1fac6c10..71efcfa45 100644
--- a/core/vm/evm.go
+++ b/core/vm/evm.go
@@ -120,7 +120,7 @@ func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas
 		snapshot = evm.StateDB.Snapshot()
 	)
 	if !evm.StateDB.Exist(addr) {
-		if PrecompiledContracts[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.BitLen() == 0 {
+		if PrecompiledContracts[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.Sign() == 0 {
 			return nil, gas, nil
 		}
 
diff --git a/core/vm/gas_table.go b/core/vm/gas_table.go
index fba1eb066..f1c62df8e 100644
--- a/core/vm/gas_table.go
+++ b/core/vm/gas_table.go
@@ -273,7 +273,7 @@ func gasExp(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem
 func gasCall(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
 	var (
 		gas            = gt.Calls
-		transfersValue = stack.Back(2).BitLen() > 0
+		transfersValue = stack.Back(2).Sign() != 0
 		address        = common.BigToAddress(stack.Back(1))
 		eip158         = evm.ChainConfig().IsEIP158(evm.BlockNumber)
 	)
@@ -316,7 +316,7 @@ func gasCall(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem
 
 func gasCallCode(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
 	gas := gt.Calls
-	if stack.Back(2).BitLen() > 0 {
+	if stack.Back(2).Sign() != 0 {
 		gas += params.CallValueTransferGas
 	}
 	memoryGas, err := memoryGasCost(mem, memorySize)
@@ -362,7 +362,7 @@ func gasSuicide(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack,
 
 		if eip158 {
 			// if empty and transfers value
-			if evm.StateDB.Empty(address) && evm.StateDB.GetBalance(contract.Address()).BitLen() > 0 {
+			if evm.StateDB.Empty(address) && evm.StateDB.GetBalance(contract.Address()).Sign() != 0 {
 				gas += gt.CreateBySuicide
 			}
 		} else if !evm.StateDB.Exist(address) {
diff --git a/core/vm/instructions.go b/core/vm/instructions.go
index 8b7bcc4d6..bfc0a668e 100644
--- a/core/vm/instructions.go
+++ b/core/vm/instructions.go
@@ -58,7 +58,7 @@ func opMul(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stac
 
 func opDiv(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	x, y := stack.pop(), stack.pop()
-	if y.Cmp(common.Big0) != 0 {
+	if y.Sign() != 0 {
 		stack.push(math.U256(x.Div(x, y)))
 	} else {
 		stack.push(new(big.Int))
@@ -71,12 +71,12 @@ func opDiv(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stac
 
 func opSdiv(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	x, y := math.S256(stack.pop()), math.S256(stack.pop())
-	if y.Cmp(common.Big0) == 0 {
+	if y.Sign() == 0 {
 		stack.push(new(big.Int))
 		return nil, nil
 	} else {
 		n := new(big.Int)
-		if evm.interpreter.intPool.get().Mul(x, y).Cmp(common.Big0) < 0 {
+		if evm.interpreter.intPool.get().Mul(x, y).Sign() < 0 {
 			n.SetInt64(-1)
 		} else {
 			n.SetInt64(1)
@@ -93,7 +93,7 @@ func opSdiv(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Sta
 
 func opMod(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	x, y := stack.pop(), stack.pop()
-	if y.Cmp(common.Big0) == 0 {
+	if y.Sign() == 0 {
 		stack.push(new(big.Int))
 	} else {
 		stack.push(math.U256(x.Mod(x, y)))
@@ -105,11 +105,11 @@ func opMod(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stac
 func opSmod(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	x, y := math.S256(stack.pop()), math.S256(stack.pop())
 
-	if y.Cmp(common.Big0) == 0 {
+	if y.Sign() == 0 {
 		stack.push(new(big.Int))
 	} else {
 		n := new(big.Int)
-		if x.Cmp(common.Big0) < 0 {
+		if x.Sign() < 0 {
 			n.SetInt64(-1)
 		} else {
 			n.SetInt64(1)
@@ -221,7 +221,7 @@ func opEq(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack
 
 func opIszero(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	x := stack.pop()
-	if x.Cmp(common.Big0) > 0 {
+	if x.Sign() > 0 {
 		stack.push(new(big.Int))
 	} else {
 		stack.push(evm.interpreter.intPool.get().SetUint64(1))
@@ -252,10 +252,11 @@ func opXor(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stac
 	evm.interpreter.intPool.put(y)
 	return nil, nil
 }
+
 func opByte(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	th, val := stack.pop(), stack.pop()
 	if th.Cmp(big.NewInt(32)) < 0 {
-		byte := evm.interpreter.intPool.get().SetInt64(int64(common.LeftPadBytes(val.Bytes(), 32)[th.Int64()]))
+		byte := evm.interpreter.intPool.get().SetInt64(int64(math.PaddedBigBytes(val, 32)[th.Int64()]))
 		stack.push(byte)
 	} else {
 		stack.push(new(big.Int))
@@ -505,7 +506,7 @@ func opJump(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Sta
 }
 func opJumpi(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	pos, cond := stack.pop(), stack.pop()
-	if cond.BitLen() > 0 {
+	if cond.Sign() != 0 {
 		if !contract.jumpdests.has(contract.CodeHash, contract.Code, pos) {
 			nop := contract.GetOp(pos.Uint64())
 			return nil, fmt.Errorf("invalid jump destination (%v) %v", nop, pos)
@@ -583,7 +584,7 @@ func opCall(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Sta
 	// Get the arguments from the memory
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
-	if value.BitLen() > 0 {
+	if value.Sign() != 0 {
 		gas += params.CallStipend
 	}
 
@@ -616,7 +617,7 @@ func opCallCode(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack
 	// Get the arguments from the memory
 	args := memory.Get(inOffset.Int64(), inSize.Int64())
 
-	if value.BitLen() > 0 {
+	if value.Sign() != 0 {
 		gas += params.CallStipend
 	}
 
diff --git a/core/vm/logger.go b/core/vm/logger.go
index 3845b1073..102a215c7 100644
--- a/core/vm/logger.go
+++ b/core/vm/logger.go
@@ -23,6 +23,7 @@ import (
 	"unicode"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 )
 
 type Storage map[common.Hash]common.Hash
@@ -180,7 +181,7 @@ func StdErrFormat(logs []StructLog) {
 		fmt.Fprintln(os.Stderr, "STACK =", len(log.Stack))
 
 		for i := len(log.Stack) - 1; i >= 0; i-- {
-			fmt.Fprintf(os.Stderr, "%04d: %x\n", len(log.Stack)-i-1, common.LeftPadBytes(log.Stack[i].Bytes(), 32))
+			fmt.Fprintf(os.Stderr, "%04d: %x\n", len(log.Stack)-i-1, math.PaddedBigBytes(log.Stack[i], 32))
 		}
 
 		const maxMem = 10