core/vm: fix incorrect computation of BLS discount (#21253)

* core/vm: fix incorrect computation of discount

During testing on Yolov1 we found that the way geth calculates the discount
is not in line with the specification. Basically what we did is calculate
128 * Bls12381GXMulGas * discount / 1000 whenever we received more than 128 pairs
of values. Correct would be to calculate k * Bls12381... for k > 128.

* core/vm: better logic for discount calculation

* core/vm: better calculation logic, added worstcase benchmarks

* core/vm: better benchmarking logic

core/vm/contracts.go

@@ -620,11 +620,12 @@ func (c *bls12381G1MultiExp) RequiredGas(input []byte) uint64 {
 		return 0
 	}
 	// Lookup discount value for G1 point, scalar value pair length
-	maxDiscountLen := len(params.Bls12381MultiExpDiscountTable)
-	if k > maxDiscountLen {
-		k = maxDiscountLen
+	var discount uint64
+	if dLen := len(params.Bls12381MultiExpDiscountTable); k < dLen {
+		discount = params.Bls12381MultiExpDiscountTable[k-1]
+	} else {
+		discount = params.Bls12381MultiExpDiscountTable[dLen-1]
 	}
-	discount := params.Bls12381MultiExpDiscountTable[k-1]
 	// Calculate gas and return the result
 	return (uint64(k) * params.Bls12381G1MulGas * discount) / 1000
 }
@@ -750,11 +751,12 @@ func (c *bls12381G2MultiExp) RequiredGas(input []byte) uint64 {
 		return 0
 	}
 	// Lookup discount value for G2 point, scalar value pair length
-	maxDiscountLen := len(params.Bls12381MultiExpDiscountTable)
-	if k > maxDiscountLen {
-		k = maxDiscountLen
+	var discount uint64
+	if dLen := len(params.Bls12381MultiExpDiscountTable); k < dLen {
+		discount = params.Bls12381MultiExpDiscountTable[k-1]
+	} else {
+		discount = params.Bls12381MultiExpDiscountTable[dLen-1]
 	}
-	discount := params.Bls12381MultiExpDiscountTable[k-1]
 	// Calculate gas and return the result
 	return (uint64(k) * params.Bls12381G2MulGas * discount) / 1000
 }

core/vm/contracts_test.go

@@ -23,6 +23,7 @@ import (
 	"io/ioutil"
 	"math/big"
 	"testing"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 )
@@ -142,14 +143,21 @@ func benchmarkPrecompiled(addr string, test precompiledTest, bench *testing.B) {
 
 	bench.Run(fmt.Sprintf("%s-Gas=%d", test.Name, contract.Gas), func(bench *testing.B) {
 		bench.ReportAllocs()
+		start := time.Now().Nanosecond()
 		bench.ResetTimer()
 		for i := 0; i < bench.N; i++ {
 			contract.Gas = reqGas
 			copy(data, in)
 			res, err = RunPrecompiledContract(p, data, contract)
 		}
 		bench.StopTimer()
+		elapsed := float64(time.Now().Nanosecond() - start)
+		if elapsed < 1 {
+			elapsed = 1
+		}
+		gasUsed := reqGas * uint64(bench.N)
 		bench.ReportMetric(float64(reqGas), "gas/op")
+		bench.ReportMetric(float64(gasUsed*1000)/elapsed, "mgas/s")
 		//Check if it is correct
 		if err != nil {
 			bench.Error(err)
@@ -320,3 +328,42 @@ func loadJsonFail(name string) ([]precompiledFailureTest, error) {
 	err = json.Unmarshal(data, &testcases)
 	return testcases, err
 }
+
+// BenchmarkPrecompiledBLS12381G1MultiExpWorstCase benchmarks the worst case we could find that still fits a gaslimit of 10MGas.
+func BenchmarkPrecompiledBLS12381G1MultiExpWorstCase(b *testing.B) {
+	task := "0000000000000000000000000000000008d8c4a16fb9d8800cce987c0eadbb6b3b005c213d44ecb5adeed713bae79d606041406df26169c35df63cf972c94be1" +
+		"0000000000000000000000000000000011bc8afe71676e6730702a46ef817060249cd06cd82e6981085012ff6d013aa4470ba3a2c71e13ef653e1e223d1ccfe9" +
+		"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+	input := task
+	for i := 0; i < 4787; i++ {
+		input = input + task
+	}
+	testcase := precompiledTest{
+		Input:       input,
+		Expected:    "0000000000000000000000000000000005a6310ea6f2a598023ae48819afc292b4dfcb40aabad24a0c2cb6c19769465691859eeb2a764342a810c5038d700f18000000000000000000000000000000001268ac944437d15923dc0aec00daa9250252e43e4b35ec7a19d01f0d6cd27f6e139d80dae16ba1c79cc7f57055a93ff5",
+		Name:        "WorstCaseG1",
+		NoBenchmark: false,
+	}
+	benchmarkPrecompiled("0c", testcase, b)
+}
+
+// BenchmarkPrecompiledBLS12381G2MultiExpWorstCase benchmarks the worst case we could find that still fits a gaslimit of 10MGas.
+func BenchmarkPrecompiledBLS12381G2MultiExpWorstCase(b *testing.B) {
+	task := "000000000000000000000000000000000d4f09acd5f362e0a516d4c13c5e2f504d9bd49fdfb6d8b7a7ab35a02c391c8112b03270d5d9eefe9b659dd27601d18f" +
+		"000000000000000000000000000000000fd489cb75945f3b5ebb1c0e326d59602934c8f78fe9294a8877e7aeb95de5addde0cb7ab53674df8b2cfbb036b30b99" +
+		"00000000000000000000000000000000055dbc4eca768714e098bbe9c71cf54b40f51c26e95808ee79225a87fb6fa1415178db47f02d856fea56a752d185f86b" +
+		"000000000000000000000000000000001239b7640f416eb6e921fe47f7501d504fadc190d9cf4e89ae2b717276739a2f4ee9f637c35e23c480df029fd8d247c7" +
+		"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+	input := task
+	for i := 0; i < 1040; i++ {
+		input = input + task
+	}
+
+	testcase := precompiledTest{
+		Input:       input,
+		Expected:    "0000000000000000000000000000000018f5ea0c8b086095cfe23f6bb1d90d45de929292006dba8cdedd6d3203af3c6bbfd592e93ecb2b2c81004961fdcbb46c00000000000000000000000000000000076873199175664f1b6493a43c02234f49dc66f077d3007823e0343ad92e30bd7dc209013435ca9f197aca44d88e9dac000000000000000000000000000000000e6f07f4b23b511eac1e2682a0fc224c15d80e122a3e222d00a41fab15eba645a700b9ae84f331ae4ed873678e2e6c9b000000000000000000000000000000000bcb4849e460612aaed79617255fd30c03f51cf03d2ed4163ca810c13e1954b1e8663157b957a601829bb272a4e6c7b8",
+		Name:        "WorstCaseG2",
+		NoBenchmark: false,
+	}
+	benchmarkPrecompiled("0f", testcase, b)
+}