core/vm: optimize copy-less data retrievals

1 files changed, 55 insertions, 48 deletions

diff --git a/core/vm/contracts.go b/core/vm/contracts.go
index c59779dac..b885d42bb 100644
--- a/core/vm/contracts.go
+++ b/core/vm/contracts.go
@@ -149,30 +149,41 @@ func (c *dataCopy) Run(in []byte) ([]byte, error) {
 // bigModExp implements a native big integer exponential modular operation.
 type bigModExp struct{}
 
+var (
+	big1      = big.NewInt(1)
+	big4      = big.NewInt(4)
+	big8      = big.NewInt(8)
+	big16     = big.NewInt(16)
+	big32     = big.NewInt(32)
+	big64     = big.NewInt(64)
+	big96     = big.NewInt(96)
+	big480    = big.NewInt(480)
+	big1024   = big.NewInt(1024)
+	big3072   = big.NewInt(3072)
+	big199680 = big.NewInt(199680)
+)
+
 // RequiredGas returns the gas required to execute the pre-compiled contract.
 func (c *bigModExp) RequiredGas(input []byte) uint64 {
-	// Pad the input with zeroes to the minimum size to read the field lengths
-	input = common.RightPadBytes(input, 96)
-
 	var (
-		baseLen = new(big.Int).SetBytes(input[:32])
-		expLen  = new(big.Int).SetBytes(input[32:64])
-		modLen  = new(big.Int).SetBytes(input[64:96])
+		baseLen = new(big.Int).SetBytes(getData(input, 0, 32))
+		expLen  = new(big.Int).SetBytes(getData(input, 32, 32))
+		modLen  = new(big.Int).SetBytes(getData(input, 64, 32))
 	)
-	input = input[96:]
-
+	if len(input) > 96 {
+		input = input[96:]
+	} else {
+		input = input[:0]
+	}
 	// Retrieve the head 32 bytes of exp for the adjusted exponent length
 	var expHead *big.Int
 	if big.NewInt(int64(len(input))).Cmp(baseLen) <= 0 {
 		expHead = new(big.Int)
 	} else {
-		offset := int(baseLen.Uint64())
-
-		input = common.RightPadBytes(input, offset+32)
-		if expLen.Cmp(big.NewInt(32)) > 0 {
-			expHead = new(big.Int).SetBytes(input[offset : offset+32])
+		if expLen.Cmp(big32) > 0 {
+			expHead = new(big.Int).SetBytes(getData(input, baseLen.Uint64(), 32))
 		} else {
-			expHead = new(big.Int).SetBytes(input[offset : offset+int(expLen.Uint64())])
+			expHead = new(big.Int).SetBytes(getData(input, baseLen.Uint64(), expLen.Uint64()))
 		}
 	}
 	// Calculate the adjusted exponent length
@@ -181,29 +192,29 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
 		msb = bitlen - 1
 	}
 	adjExpLen := new(big.Int)
-	if expLen.Cmp(big.NewInt(32)) > 0 {
-		adjExpLen.Sub(expLen, big.NewInt(32))
-		adjExpLen.Mul(big.NewInt(8), adjExpLen)
+	if expLen.Cmp(big32) > 0 {
+		adjExpLen.Sub(expLen, big32)
+		adjExpLen.Mul(big8, adjExpLen)
 	}
 	adjExpLen.Add(adjExpLen, big.NewInt(int64(msb)))
 
 	// Calculate the gas cost of the operation
 	gas := new(big.Int).Set(math.BigMax(modLen, baseLen))
 	switch {
-	case gas.Cmp(big.NewInt(64)) <= 0:
+	case gas.Cmp(big64) <= 0:
 		gas.Mul(gas, gas)
-	case gas.Cmp(big.NewInt(1024)) <= 0:
+	case gas.Cmp(big1024) <= 0:
 		gas = new(big.Int).Add(
-			new(big.Int).Div(new(big.Int).Mul(gas, gas), big.NewInt(4)),
-			new(big.Int).Sub(new(big.Int).Mul(big.NewInt(96), gas), big.NewInt(3072)),
+			new(big.Int).Div(new(big.Int).Mul(gas, gas), big4),
+			new(big.Int).Sub(new(big.Int).Mul(big96, gas), big3072),
 		)
 	default:
 		gas = new(big.Int).Add(
-			new(big.Int).Div(new(big.Int).Mul(gas, gas), big.NewInt(16)),
-			new(big.Int).Sub(new(big.Int).Mul(big.NewInt(480), gas), big.NewInt(199680)),
+			new(big.Int).Div(new(big.Int).Mul(gas, gas), big16),
+			new(big.Int).Sub(new(big.Int).Mul(big480, gas), big199680),
 		)
 	}
-	gas.Mul(gas, math.BigMax(adjExpLen, big.NewInt(1)))
+	gas.Mul(gas, math.BigMax(adjExpLen, big1))
 	gas.Div(gas, new(big.Int).SetUint64(params.ModExpQuadCoeffDiv))
 
 	if gas.BitLen() > 64 {
@@ -213,23 +224,25 @@ func (c *bigModExp) RequiredGas(input []byte) uint64 {
 }
 
 func (c *bigModExp) Run(input []byte) ([]byte, error) {
-	// Pad the input with zeroes to the minimum size to read the field lengths
-	input = common.RightPadBytes(input, 96)
-
 	var (
-		baseLen = new(big.Int).SetBytes(input[:32]).Uint64()
-		expLen  = new(big.Int).SetBytes(input[32:64]).Uint64()
-		modLen  = new(big.Int).SetBytes(input[64:96]).Uint64()
+		baseLen = new(big.Int).SetBytes(getData(input, 0, 32)).Uint64()
+		expLen  = new(big.Int).SetBytes(getData(input, 32, 32)).Uint64()
+		modLen  = new(big.Int).SetBytes(getData(input, 64, 32)).Uint64()
 	)
-	input = input[96:]
-
-	// Pad the input with zeroes to the minimum size to read the field contents
-	input = common.RightPadBytes(input, int(baseLen+expLen+modLen))
-
+	if len(input) > 96 {
+		input = input[96:]
+	} else {
+		input = input[:0]
+	}
+	// Handle a special case when both the base and mod length is zero
+	if baseLen == 0 && modLen == 0 {
+		return []byte{}, nil
+	}
+	// Retrieve the operands and execute the exponentiation
 	var (
-		base = new(big.Int).SetBytes(input[:baseLen])
-		exp  = new(big.Int).SetBytes(input[baseLen : baseLen+expLen])
-		mod  = new(big.Int).SetBytes(input[baseLen+expLen : baseLen+expLen+modLen])
+		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))
 	)
 	if mod.BitLen() == 0 {
 		// Modulo 0 is undefined, return zero
@@ -286,14 +299,11 @@ func (c *bn256Add) RequiredGas(input []byte) uint64 {
 }
 
 func (c *bn256Add) Run(input []byte) ([]byte, error) {
-	// Ensure we have enough data to operate on
-	input = common.RightPadBytes(input, 128)
-
-	x, err := newCurvePoint(input[:64])
+	x, err := newCurvePoint(getData(input, 0, 64))
 	if err != nil {
 		return nil, err
 	}
-	y, err := newCurvePoint(input[64:128])
+	y, err := newCurvePoint(getData(input, 64, 64))
 	if err != nil {
 		return nil, err
 	}
@@ -310,14 +320,11 @@ func (c *bn256ScalarMul) RequiredGas(input []byte) uint64 {
 }
 
 func (c *bn256ScalarMul) Run(input []byte) ([]byte, error) {
-	// Ensure we have enough data to operate on
-	input = common.RightPadBytes(input, 96)
-
-	p, err := newCurvePoint(input[:64])
+	p, err := newCurvePoint(getData(input, 0, 64))
 	if err != nil {
 		return nil, err
 	}
-	p.ScalarMult(p, new(big.Int).SetBytes(input[64:96]))
+	p.ScalarMult(p, new(big.Int).SetBytes(getData(input, 64, 32)))
 	return p.Marshal(), nil
 }