eth: opt incHash

[cuiweixie]

test and bench:

package main

import (
	"bytes"
	"testing"

	"github.com/ethereum/go-ethereum/common"
	"github.com/holiman/uint256"
)

func incHash(h common.Hash) common.Hash {
	var a uint256.Int
	a.SetBytes32(h[:])
	a.AddUint64(&a, 1)
	return common.Hash(a.Bytes32())
}

func incHashFast(h common.Hash) common.Hash {
	for i := len(h) - 1; i >= 0; i-- {
		h[i]++
		if h[i] != 0 {
			break
		}
	}
	return h
}

func TestIncHashCorrectness(t *testing.T) {
	testCases := []common.Hash{
		common.HexToHash("0x0"),
		common.HexToHash("0x01"),
		common.HexToHash("0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), // 最大值
		common.HexToHash("0x00000000000000000000000000000000000000000000000000000000ffffffff"), // 边界
	}

	for _, tc := range testCases {
		got1 := incHash(tc)
		got2 := incHashFast(tc)

		if !bytes.Equal(got1[:], got2[:]) {
			t.Errorf("Mismatch for %x: uint256=%x fast=%x", tc, got1, got2)
		}
	}
}

// Benchmark origin
func BenchmarkIncHash(b *testing.B) {
	var h common.Hash
	for i := 0; i < b.N; i++ {
		_ = incHash(h)
	}
}

// Benchmark optimized
func BenchmarkIncHashFast(b *testing.B) {
	var h common.Hash
	for i := 0; i < b.N; i++ {
		_ = incHashFast(h)
	}
}

goos: darwin
goarch: arm64
pkg: github.com/cuiweixie/mylabs/tests/inc_hash
cpu: Apple M1 Pro
BenchmarkIncHash
BenchmarkIncHash-10        	175488444	         6.941 ns/op
BenchmarkIncHashFast
BenchmarkIncHashFast-10    	1000000000	         0.8142 ns/op
PASS