improve func packCommand performance, the more args the more obvious eff...

[walu]

execute 100K times: packCommand("GET", "USERl-list", 123)
improve nearly 100%, 207->117

[xuyu]

func packCommand(args ...interface{}) ([]byte, error) {
    buf := buffers.GetBuffer()
    defer buffers.PutBuffer(buf)
    if _, err := fmt.Fprintf(buf, "*%d\r\n", len(args)); err != nil {
        return nil, err
    }
    var s string
    for _, arg := range args {
        switch v := arg.(type) {
        case string:
            s = v
        case int:
            s = strconv.Itoa(v)
        case int64:
            s = strconv.FormatInt(v, 10)
        case uint64:
            s = strconv.FormatUint(v, 10)
        case float64:
            s = strconv.FormatFloat(v, 'g', -1, 64)
        default:
            return nil, errors.New("invalid argument type when pack command")
        }
        if _, err := fmt.Fprintf(buf, "$%d\r\n%s\r\n", len(s), s); err != nil {
            return nil, err
        }
    }
    return buf.Bytes(), nil
}

func packCommand2(args ...interface{}) ([]byte, error) {
    var s, ret string
    for _, arg := range args {
        switch v := arg.(type) {
        case string:
            s = v
        case int:
            s = strconv.Itoa(v)
        case int64:
            s = strconv.FormatInt(v, 10)
        case uint64:
            s = strconv.FormatUint(v, 10)
        case float64:
            s = strconv.FormatFloat(v, 'g', -1, 64)
        default:
            return nil, errors.New("invalid argument type when pack command")
        }
        ret += "$" + strconv.Itoa(len(s)) + "\r\n" + s + "\r\n"
    }
    return []byte(ret), nil
}

func numLen(i int64) int64 {
    n, pos10 := int64(1), int64(10)
    if i < 0 {
        i = -i
        n++
    }
    for i >= pos10 {
        n++
        pos10 *= 10
    }
    return n
}

func packCommand3(args ...interface{}) ([]byte, error) {
    n := len(args)
    res := make([]byte, 0, 16*n)
    res = append(res, byte('*'))
    res = strconv.AppendInt(res, int64(n), 10)
    res = append(res, byte('\r'), byte('\n'))
    for _, arg := range args {
        res = append(res, byte('$'))
        switch v := arg.(type) {
        case []byte:
            res = strconv.AppendInt(res, int64(len(v)), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = append(res, v...)
        case string:
            res = strconv.AppendInt(res, int64(len(v)), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = append(res, []byte(v)...)
        case int:
            res = strconv.AppendInt(res, numLen(int64(v)), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = strconv.AppendInt(res, int64(v), 10)
        case int64:
            res = strconv.AppendInt(res, numLen(v), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = strconv.AppendInt(res, int64(v), 10)
        case uint64:
            res = strconv.AppendInt(res, numLen(int64(v)), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = strconv.AppendUint(res, uint64(v), 10)
        case float64:
            var buf []byte
            buf = strconv.AppendFloat(buf, v, 'g', -1, 64)
            res = strconv.AppendInt(res, int64(len(buf)), 10)
            res = append(res, byte('\r'), byte('\n'))
            res = append(res, buf...)
        default:
            return nil, errors.New("invalid argument type when pack command")
        }
        res = append(res, byte('\r'), byte('\n'))
    }
    return res, nil
}

[xuyu]

func BenchmarkPackCommand(b *testing.B) {
    var (
        s = "Command"
        n = 123
        f = 7.11
    )
    for i := 0; i < b.N; i++ {
        packCommand(s, n, f)
    }
}

func BenchmarkPackCommand2(b *testing.B) {
    var (
        s = "Command"
        n = 123
        f = 7.11
    )
    for i := 0; i < b.N; i++ {
        packCommand2(s, n, f)
    }
}

func BenchmarkPackCommand3(b *testing.B) {
    var (
        s = "Command"
        n = 123
        f = 7.11
    )
    for i := 0; i < b.N; i++ {
        packCommand3(s, n, f)
    }
}

[xuyu]

go test -test.bench="^BenchmarkPackCommand" -test.benchmem=true -test.run="^$"

BenchmarkPackCommand      500000          2562 ns/op         123 B/op          8 allocs/op
BenchmarkPackCommand2    1000000          1678 ns/op         248 B/op         13 allocs/op
BenchmarkPackCommand3    1000000          1189 ns/op          96 B/op          6 allocs/op