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

accounts/abi/bind/backends/simulated.go

@@ -237,7 +237,7 @@ func (b *SimulatedBackend) callContract(ctx context.Context, call ethereum.CallM
 	if call.GasPrice == nil {
 		call.GasPrice = big.NewInt(1)
 	}
-	if call.Gas == nil || call.Gas.BitLen() == 0 {
+	if call.Gas == nil || call.Gas.Sign() == 0 {
 		call.Gas = big.NewInt(50000000)
 	}
 	if call.Value == nil {

accounts/abi/numbers.go

@@ -59,7 +59,7 @@ var (
 
 // U256 converts a big Int into a 256bit EVM number.
 func U256(n *big.Int) []byte {
-	return common.LeftPadBytes(math.U256(n).Bytes(), 32)
+	return math.PaddedBigBytes(math.U256(n), 32)
 }
 
 // packNum packs the given number (using the reflect value) and will cast it to appropriate number representation

accounts/abi/packing.go

@@ -20,6 +20,7 @@ import (
 	"reflect"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 )
 
 // packBytesSlice packs the given bytes as [L, V] as the canonical representation
@@ -45,9 +46,9 @@ func packElement(t Type, reflectValue reflect.Value) []byte {
 		return common.LeftPadBytes(reflectValue.Bytes(), 32)
 	case BoolTy:
 		if reflectValue.Bool() {
-			return common.LeftPadBytes(common.Big1.Bytes(), 32)
+			return math.PaddedBigBytes(common.Big1, 32)
 		} else {
-			return common.LeftPadBytes(common.Big0.Bytes(), 32)
+			return math.PaddedBigBytes(common.Big0, 32)
 		}
 	case BytesTy:
 		if reflectValue.Kind() == reflect.Array {

accounts/keystore/keystore_passphrase.go

@@ -36,6 +36,7 @@ import (
 	"path/filepath"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/crypto/randentropy"
 	"github.com/pborman/uuid"
@@ -115,8 +116,7 @@ func EncryptKey(key *Key, auth string, scryptN, scryptP int) ([]byte, error) {
 		return nil, err
 	}
 	encryptKey := derivedKey[:16]
-	keyBytes0 := crypto.FromECDSA(key.PrivateKey)
-	keyBytes := common.LeftPadBytes(keyBytes0, 32)
+	keyBytes := math.PaddedBigBytes(key.PrivateKey.D, 32)
 
 	iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
 	cipherText, err := aesCTRXOR(encryptKey, keyBytes, iv)

accounts/usbwallet/ledger_wallet.go

@@ -416,7 +416,7 @@ func (w *ledgerWallet) selfDerive() {
 				break
 			}
 			// If the next account is empty, stop self-derivation, but add it nonetheless
-			if balance.BitLen() == 0 && nonce == 0 {
+			if balance.Sign() == 0 && nonce == 0 {
 				empty = true
 			}
 			// We've just self-derived a new account, start tracking it locally

common/math/big.go

@@ -28,6 +28,13 @@ var (
 	MaxBig256 = new(big.Int).Set(tt256m1)
 )
 
+const (
+	// number of bits in a big.Word
+	wordBits = 32 << (uint64(^big.Word(0)) >> 63)
+	// number of bytes in a big.Word
+	wordBytes = wordBits / 8
+)
+
 // ParseBig256 parses s as a 256 bit integer in decimal or hexadecimal syntax.
 // Leading zeros are accepted. The empty string parses as zero.
 func ParseBig256(s string) (*big.Int, bool) {
@@ -91,12 +98,25 @@ func FirstBitSet(v *big.Int) int {
 // PaddedBigBytes encodes a big integer as a big-endian byte slice. The length
 // of the slice is at least n bytes.
 func PaddedBigBytes(bigint *big.Int, n int) []byte {
-	bytes := bigint.Bytes()
-	if len(bytes) >= n {
-		return bytes
+	if bigint.BitLen()/8 >= n {
+		return bigint.Bytes()
 	}
 	ret := make([]byte, n)
-	return append(ret[:len(ret)-len(bytes)], bytes...)
+	ReadBits(bigint, ret)
+	return ret
+}
+
+// ReadBits encodes the absolute value of bigint as big-endian bytes. Callers must ensure
+// that buf has enough space. If buf is too short the result will be incomplete.
+func ReadBits(bigint *big.Int, buf []byte) {
+	i := len(buf)
+	for _, d := range bigint.Bits() {
+		for j := 0; j < wordBytes && i > 0; j++ {
+			i--
+			buf[i] = byte(d)
+			d >>= 8
+		}
+	}
 }
 
 // U256 encodes as a 256 bit two's complement number. This operation is destructive.
@@ -119,9 +139,6 @@ func S256(x *big.Int) *big.Int {
 	}
 }
 
-// wordSize is the size number of bits in a big.Word.
-const wordSize = 32 << (uint64(^big.Word(0)) >> 63)
-
 // Exp implements exponentiation by squaring.
 // Exp returns a newly-allocated big integer and does not change
 // base or exponent. The result is truncated to 256 bits.
@@ -131,7 +148,7 @@ func Exp(base, exponent *big.Int) *big.Int {
 	result := big.NewInt(1)
 
 	for _, word := range exponent.Bits() {
-		for i := 0; i < wordSize; i++ {
+		for i := 0; i < wordBits; i++ {
 			if word&1 == 1 {
 				U256(result.Mul(result, base))
 			}

common/math/big_test.go

@@ -18,6 +18,7 @@ package math
 
 import (
 	"bytes"
+	"encoding/hex"
 	"math/big"
 	"testing"
 )
@@ -131,6 +132,28 @@ func TestPaddedBigBytes(t *testing.T) {
 	}
 }
 
+func BenchmarkPaddedBigBytes(b *testing.B) {
+	bigint := MustParseBig256("123456789123456789123456789123456789")
+	for i := 0; i < b.N; i++ {
+		PaddedBigBytes(bigint, 32)
+	}
+}
+
+func TestReadBits(t *testing.T) {
+	check := func(input string) {
+		want, _ := hex.DecodeString(input)
+		int, _ := new(big.Int).SetString(input, 16)
+		buf := make([]byte, len(want))
+		ReadBits(int, buf)
+		if !bytes.Equal(buf, want) {
+			t.Errorf("have: %x\nwant: %x", buf, want)
+		}
+	}
+	check("000000000000000000000000000000000000000000000000000000FEFCF3F8F0")
+	check("0000000000012345000000000000000000000000000000000000FEFCF3F8F0")
+	check("18F8F8F1000111000110011100222004330052300000000000000000FEFCF3F8F0")
+}
+
 func TestU256(t *testing.T) {
 	tests := []struct{ x, y *big.Int }{
 		{x: big.NewInt(0), y: big.NewInt(0)},

contracts/chequebook/cheque.go

@@ -247,7 +247,7 @@ func (self *Chequebook) Issue(beneficiary common.Address, amount *big.Int) (ch *
 	defer self.lock.Unlock()
 	self.lock.Lock()
 
-	if amount.Cmp(common.Big0) <= 0 {
+	if amount.Sign() <= 0 {
 		return nil, fmt.Errorf("amount must be greater than zero (%v)", amount)
 	}
 	if self.balance.Cmp(amount) < 0 {
@@ -515,7 +515,7 @@ func (self *Inbox) autoCash(cashInterval time.Duration) {
 		self.quit = nil
 	}
 	// if maxUncashed is set to 0, then autocash on receipt
-	if cashInterval == time.Duration(0) || self.maxUncashed != nil && self.maxUncashed.Cmp(common.Big0) == 0 {
+	if cashInterval == time.Duration(0) || self.maxUncashed != nil && self.maxUncashed.Sign() == 0 {
 		return
 	}
 
@@ -597,7 +597,7 @@ func (self *Cheque) Verify(signerKey *ecdsa.PublicKey, contract, beneficiary com
 	amount := new(big.Int).Set(self.Amount)
 	if sum != nil {
 		amount.Sub(amount, sum)
-		if amount.Cmp(common.Big0) <= 0 {
+		if amount.Sign() <= 0 {
 			return nil, fmt.Errorf("incorrect amount: %v <= 0", amount)
 		}
 	}

contracts/chequebook/cheque_test.go

@@ -88,7 +88,7 @@ func TestIssueAndReceive(t *testing.T) {
 		t.Fatalf("expected no error, got %v", err)
 	}
 
-	if chbook.Balance().Cmp(common.Big0) != 0 {
+	if chbook.Balance().Sign() != 0 {
 		t.Errorf("expected: %v, got %v", "0", chbook.Balance())
 	}
 

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
 		}
 	}

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))

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
 	}
 

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{}

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)
 	}

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())
 	}
 }

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
 	}
 

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
 		}
 

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) {

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
 	}
 

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

crypto/secp256k1/curve.go

@@ -36,6 +36,8 @@ import (
 	"math/big"
 	"sync"
 	"unsafe"
+
+	"github.com/ethereum/go-ethereum/common/math"
 )
 
 /*
@@ -230,8 +232,8 @@ func (BitCurve *BitCurve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int,
 
 	// Do the multiplication in C, updating point.
 	point := make([]byte, 64)
-	readBits(point[:32], Bx)
-	readBits(point[32:], By)
+	math.ReadBits(Bx, point[:32])
+	math.ReadBits(By, point[32:])
 	pointPtr := (*C.uchar)(unsafe.Pointer(&point[0]))
 	scalarPtr := (*C.uchar)(unsafe.Pointer(&scalar[0]))
 	res := C.secp256k1_pubkey_scalar_mul(context, pointPtr, scalarPtr)

crypto/secp256k1/curve_test.go

@@ -1,39 +0,0 @@
-// Copyright 2015 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 secp256k1
-
-import (
-	"bytes"
-	"encoding/hex"
-	"math/big"
-	"testing"
-)
-
-func TestReadBits(t *testing.T) {
-	check := func(input string) {
-		want, _ := hex.DecodeString(input)
-		int, _ := new(big.Int).SetString(input, 16)
-		buf := make([]byte, len(want))
-		readBits(buf, int)
-		if !bytes.Equal(buf, want) {
-			t.Errorf("have: %x\nwant: %x", buf, want)
-		}
-	}
-	check("000000000000000000000000000000000000000000000000000000FEFCF3F8F0")
-	check("0000000000012345000000000000000000000000000000000000FEFCF3F8F0")
-	check("18F8F8F1000111000110011100222004330052300000000000000000FEFCF3F8F0")
-}

crypto/secp256k1/secp256.go

@@ -38,7 +38,6 @@ import "C"
 
 import (
 	"errors"
-	"math/big"
 	"unsafe"
 )
 
@@ -129,16 +128,3 @@ func checkSignature(sig []byte) error {
 	}
 	return nil
 }
-
-// reads num into buf as big-endian bytes.
-func readBits(buf []byte, num *big.Int) {
-	const wordLen = int(unsafe.Sizeof(big.Word(0)))
-	i := len(buf)
-	for _, d := range num.Bits() {
-		for j := 0; j < wordLen && i > 0; j++ {
-			i--
-			buf[i] = byte(d)
-			d >>= 8
-		}
-	}
-}

crypto/secp256k1/secp256_test.go

@@ -24,6 +24,7 @@ import (
 	"encoding/hex"
 	"testing"
 
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/crypto/randentropy"
 )
 
@@ -35,9 +36,7 @@ func generateKeyPair() (pubkey, privkey []byte) {
 		panic(err)
 	}
 	pubkey = elliptic.Marshal(S256(), key.X, key.Y)
-	privkey = make([]byte, 32)
-	readBits(privkey, key.D)
-	return pubkey, privkey
+	return pubkey, math.PaddedBigBytes(key.D, 32)
 }
 
 func randSig() []byte {

crypto/signature_cgo.go

@@ -23,7 +23,7 @@ import (
 	"crypto/elliptic"
 	"fmt"
 
-	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 )
 
@@ -53,7 +53,7 @@ func Sign(hash []byte, prv *ecdsa.PrivateKey) (sig []byte, err error) {
 	if len(hash) != 32 {
 		return nil, fmt.Errorf("hash is required to be exactly 32 bytes (%d)", len(hash))
 	}
-	seckey := common.LeftPadBytes(prv.D.Bytes(), prv.Params().BitSize/8)
+	seckey := math.PaddedBigBytes(prv.D, prv.Params().BitSize/8)
 	defer zeroBytes(seckey)
 	return secp256k1.Sign(hash, seckey)
 }

internal/ethapi/api.go

@@ -596,10 +596,10 @@ func (s *PublicBlockChainAPI) doCall(ctx context.Context, args CallArgs, blockNr
 	}
 	// Set default gas & gas price if none were set
 	gas, gasPrice := args.Gas.ToInt(), args.GasPrice.ToInt()
-	if gas.BitLen() == 0 {
+	if gas.Sign() == 0 {
 		gas = big.NewInt(50000000)
 	}
-	if gasPrice.BitLen() == 0 {
+	if gasPrice.Sign() == 0 {
 		gasPrice = new(big.Int).SetUint64(defaultGasPrice)
 	}
 
@@ -653,7 +653,7 @@ func (s *PublicBlockChainAPI) Call(ctx context.Context, args CallArgs, blockNr r
 func (s *PublicBlockChainAPI) EstimateGas(ctx context.Context, args CallArgs) (*hexutil.Big, error) {
 	// Binary search the gas requirement, as it may be higher than the amount used
 	var lo, hi uint64
-	if (*big.Int)(&args.Gas).BitLen() > 0 {
+	if (*big.Int)(&args.Gas).Sign() != 0 {
 		hi = (*big.Int)(&args.Gas).Uint64()
 	} else {
 		// Retrieve the current pending block to act as the gas ceiling
@@ -720,7 +720,7 @@ func FormatLogs(structLogs []vm.StructLog) []StructLogRes {
 		}
 
 		for i, stackValue := range trace.Stack {
-			formattedStructLogs[index].Stack[i] = fmt.Sprintf("%x", common.LeftPadBytes(stackValue.Bytes(), 32))
+			formattedStructLogs[index].Stack[i] = fmt.Sprintf("%x", math.PaddedBigBytes(stackValue, 32))
 		}
 
 		for i := 0; i+32 <= len(trace.Memory); i += 32 {

light/state_object.go

@@ -202,7 +202,7 @@ func (self *StateObject) Copy() *StateObject {
 
 // empty returns whether the account is considered empty.
 func (self *StateObject) empty() bool {
-	return self.nonce == 0 && self.balance.BitLen() == 0 && bytes.Equal(self.codeHash, emptyCodeHash)
+	return self.nonce == 0 && self.balance.Sign() == 0 && bytes.Equal(self.codeHash, emptyCodeHash)
 }
 
 // Balance returns the account balance

light/txpool.go

@@ -365,7 +365,7 @@ func (pool *TxPool) validateTx(ctx context.Context, 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 core.ErrNegativeValue
 	}
 

swarm/services/swap/swap/swap.go

@@ -22,7 +22,6 @@ import (
 	"sync"
 	"time"
 
-	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/log"
 )
 
@@ -120,11 +119,11 @@ func (self *Swap) SetRemote(remote *Profile) {
 	self.lock.Lock()
 
 	self.remote = remote
-	if self.Sells && (remote.BuyAt.Cmp(common.Big0) <= 0 || self.local.SellAt.Cmp(common.Big0) <= 0 || remote.BuyAt.Cmp(self.local.SellAt) < 0) {
+	if self.Sells && (remote.BuyAt.Sign() <= 0 || self.local.SellAt.Sign() <= 0 || remote.BuyAt.Cmp(self.local.SellAt) < 0) {
 		self.Out.Stop()
 		self.Sells = false
 	}
-	if self.Buys && (remote.SellAt.Cmp(common.Big0) <= 0 || self.local.BuyAt.Cmp(common.Big0) <= 0 || self.local.BuyAt.Cmp(self.remote.SellAt) < 0) {
+	if self.Buys && (remote.SellAt.Sign() <= 0 || self.local.BuyAt.Sign() <= 0 || self.local.BuyAt.Cmp(self.remote.SellAt) < 0) {
 		self.In.Stop()
 		self.Buys = false
 	}

tests/util.go

@@ -71,7 +71,7 @@ func checkLogs(tlog []Log, logs []*types.Log) error {
 					}
 				}
 			}
-			genBloom := common.LeftPadBytes(types.LogsBloom([]*types.Log{logs[i]}).Bytes(), 256)
+			genBloom := math.PaddedBigBytes(types.LogsBloom([]*types.Log{logs[i]}), 256)
 
 			if !bytes.Equal(genBloom, common.Hex2Bytes(log.BloomF)) {
 				return fmt.Errorf("bloom mismatch")