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

1 files changed, 4 insertions, 4 deletions

diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index 08e9c7370..5b7115e44 100644
--- a/internal/ethapi/api.go
+++ b/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 {