fix(CharsetToUTF8): use strings.Builder

[konart]

This PR changes how returning string is created in CharsetToUTF8 function.

Code

import (
	"strings"
)

var str string

func CharsetToUTF8(s []byte) {
	buf := make([]rune, 0, len(s))
	for i := 0; i < len(s); i++ {
		ch := cp950.sb[s[i]]
		if ch == -1 {
			if i+1 == len(s) {
				ch = 0xfffd
			} else {
				n := int(s[i+1]) + (int(s[i]) << 8)
				i++
				var ok bool
				ch, ok = cp950.db[n]
				if !ok {
					ch = 0xfffd
				}
			}
		}
		buf = append(buf, ch)
	}
	str = string(buf)
}

func CharsetToUTF8_2(s []byte) {
	b := strings.Builder{}
	b.Grow(len(s))
	for i := 0; i < len(s); i++ {
		ch := cp950.sb[s[i]]
		if ch == -1 {
			if i+1 == len(s) {
				ch = 0xfffd
			} else {
				n := int(s[i+1]) + (int(s[i]) << 8)
				i++
				var ok bool
				ch, ok = cp950.db[n]
				if !ok {
					ch = 0xfffd
				}
			}
		}
		b.WriteRune(ch)
	}
	str = b.String()
}

Benchmarks:

import (
	"testing"
)

const (
	testStringASCII = "qwertyuiopasdfghjklzxcvbnm1234567890!@#$%^&*()"
	testStringMixed = "IUd=h'1c^-~+%He@.nCTB{uAiwq23sN)a54JyVtEp;D>m№FWo(Q0ы^]|,$$фф*(у`ыт|ипксю;лр`р{`~*йа#б~а_'юг"
)

func BenchmarkCharsetToUTF8ASCIIToString(b *testing.B) {
	bs := []byte(testStringASCII)
	for i := 0; i < b.N; i++ {
		CharsetToUTF8(bs)
	}
}

func BenchmarkCharsetToUTF8ASCIIBuilder(b *testing.B) {
	bs := []byte(testStringASCII)
	for i := 0; i < b.N; i++ {
		CharsetToUTF8_2(bs)
	}
}

func BenchmarkCharsetToUTF8MixedToString(b *testing.B) {
	bs := []byte(testStringMixed)
	for i := 0; i < b.N; i++ {
		CharsetToUTF8(bs)
	}
}

func BenchmarkCharsetToUTF8MixedBuilder(b *testing.B) {
	bs := []byte(testStringMixed)
	for i := 0; i < b.N; i++ {
		CharsetToUTF8_2(bs)
	}
}

Benchmarks results:

❯ go test -bench=. -benchmem -benchtime=10000000x
goos: darwin
goarch: amd64
pkg: benchrune
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkCharsetToUTF8ASCIIToString-12          10000000               361.5 ns/op           256 B/op          2 allocs/op
BenchmarkCharsetToUTF8ASCIIBuilder-12           10000000               196.9 ns/op            48 B/op          1 allocs/op
BenchmarkCharsetToUTF8MixedToString-12          10000000               949.6 ns/op           624 B/op          2 allocs/op
BenchmarkCharsetToUTF8MixedBuilder-12           10000000               685.1 ns/op           368 B/op          2 allocs/op

[shueybubbles]

thx for the submission!

[shueybubbles]