utf8len.FromFirstByte

func FromFirstByte(c byte) int

A function that determines the byte length of the first UTF-8 character based on its initial byte.

This approach is more efficient than Go's standard utf8.DecodeRuneInString because it skips computing the Unicode code point.

If the provided byte is not a valid starting byte for a UTF-8 sequence, the function returns zero.

main_test.go

package utf8len_test

import (
    "fmt"
    "testing"
    "unicode/utf8"

    "github.com/hymkor/go-utf8len"
)

var source = [0x110000]string{}

func init() {
    //println("setup test table")
    for c := range source {
        source[c] = fmt.Sprintf("%c", c)
    }
    //println("done")
}

func TestFromFirstByte(t *testing.T) {
    for _, s := range source {
        _, expect := utf8.DecodeRuneInString(s)
        result := utf8len.FromFirstByte(s[0])
        if expect != result {
            t.Fatalf("expect %#v,but %#v for %#v", expect, result, s)
        }
        // println(source,expect,result)
    }
}

func BenchmarkFromFirstByte(b *testing.B) {
    for c := 0; c < b.N; c++ {
        utf8len.FromFirstByte(source[c%len(source)][0])
    }
}

func BenchmarkDecodeRuneInString(b *testing.B) {
    for c := 0; c < b.N; c++ {
        _, _ = utf8.DecodeRuneInString(source[c%len(source)])
    }
}

go test -bench . -benchmem

go test -bench . -benchmem
goos: windows
goarch: amd64
pkg: github.com/hymkor/go-utf8len
cpu: Intel(R) Core(TM) i5-6500T CPU @ 2.50GHz
BenchmarkFromFirstByte-4        	378031695	         3.256 ns/op	       0 B/op	       0 allocs/op
BenchmarkDecodeRuneInString-4   	138281330	         8.378 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/hymkor/go-utf8len	4.058s

License

hymkor/go-utf8len

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