core/vm: use optimized bigint (ethereum#26021)

core/vm/contracts.go

@@ -29,8 +29,7 @@ import (
 	"github.com/ethereum/go-ethereum/crypto/bls12381"
 	"github.com/ethereum/go-ethereum/crypto/bn256"
 	"github.com/ethereum/go-ethereum/params"
-
-	//lint:ignore SA1019 Needed for precompile
+	big2 "github.com/holiman/big"
 	"golang.org/x/crypto/ripemd160"
 )
 
@@ -266,9 +265,10 @@ var (
 // modexpMultComplexity implements bigModexp multComplexity formula, as defined in EIP-198
 //
 // def mult_complexity(x):
-//    if x <= 64: return x ** 2
-//    elif x <= 1024: return x ** 2 // 4 + 96 * x - 3072
-//    else: return x ** 2 // 16 + 480 * x - 199680
+//
+//	if x <= 64: return x ** 2
+//	elif x <= 1024: return x ** 2 // 4 + 96 * x - 3072
+//	else: return x ** 2 // 16 + 480 * x - 199680
 //
 // where is x is max(length_of_MODULUS, length_of_BASE)
 func modexpMultComplexity(x *big.Int) *big.Int {
@@ -379,15 +379,22 @@ func (c *bigModExp) Run(input []byte) ([]byte, error) {
 	}
 	// Retrieve the operands and execute the exponentiation
 	var (
-		base = new(big.Int).SetBytes(getData(input, 0, baseLen))
-		exp  = new(big.Int).SetBytes(getData(input, baseLen, expLen))
-		mod  = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
+		base = new(big2.Int).SetBytes(getData(input, 0, baseLen))
+		exp  = new(big2.Int).SetBytes(getData(input, baseLen, expLen))
+		mod  = new(big2.Int).SetBytes(getData(input, baseLen+expLen, modLen))
+		v    []byte
 	)
-	if mod.BitLen() == 0 {
+	switch {
+	case mod.BitLen() == 0:
 		// Modulo 0 is undefined, return zero
 		return common.LeftPadBytes([]byte{}, int(modLen)), nil
+	case base.BitLen() == 1: // a bit length of 1 means it's 1 (or -1).
+		//If base == 1, then we can just return base % mod (if mod >= 1, which it is)
+		v = base.Mod(base, mod).Bytes()
+	default:
+		v = base.Exp(base, exp, mod).Bytes()
 	}
-	return common.LeftPadBytes(base.Exp(base, exp, mod).Bytes(), int(modLen)), nil
+	return common.LeftPadBytes(v, int(modLen)), nil
 }
 
 // newCurvePoint unmarshals a binary blob into a bn256 elliptic curve point,