[JUG-Indonesia] [Challenge] String to double conversion

[T Budi S]

Dear juggers,

Mumpung lg hot2nya bahas thread puts vs System.out.println,
gw ada 1 challenge utk optimize string to double conversion method
dari class java.lang.Double:

        public static Double valueOf(double d)

Kenapa gw butuh utk optimize ini? Krn di project yg sedang gw kerjakan
skr, method valueOf memakan 90% ! process time dr keseluruhan process.
FYI, data yg dibaca sekitar 10 ribu (nantinya akan jadi ratusan ribu),
setiap row terdiri dari 8 column, di mana setiap column-nya berisi
data seperti ini:

13.4375:17.1875:22.5:22.8125:23.4375:3:5:4:3:3:3:5:5:3:4:4:5:3:2:6:2:5:3:6:4:2:5:6:3:5:3:2:7:6:5:2:3:6:5:5:2:4:6:4:6:5:3:4:5:3:3:3:5:6:5:2:2:6:7:5:1:3:4:7:6:4:2:1:5:4:3:3:4:5:6:3:1:6:3:5:1:4:2:3:3:3.5:3.75:3.75:4:3.75:3:3.25:5.25:5:5:2.75:2.75:5.25:4.25:5.25:1.5:4:3.75:5:4.75:3:5:3.75:3.5:4.25:2.25:3.5:6.25:4.5:5.25:2.75:2.75:4.75:6.25:4.75:2.75:2.5:3.25:4:4.5:2.75:4.25:5.5:3.75:4.25:2.5:4.25:4.5:4.25:5.25:3.75:2.75:3.5

Waktu yg dibutuhkan utk meload semua data ini adalah 4547 ms.

Kemudian saya mencoba utk menggantikan Double.valueOf method
dgn method bikinan saya sendiri, & mendapatkan hasil 3718 ms.

Code-nya adalah sbb:

==============================================
public class ConversionHelper
{

    public static double stringToDouble(String s)
    {
        char[] cc = s.toCharArray();
        int length = cc.length;
        if (length == 0)
            return 0;

        int i = 0;

        double negation = 1;
        if (cc[0] == '-')
        {
            negation = -1;
            i++;
        }

        int point = -1;
        int value = 0;
        for (; i<length; i++)
        {
            if (cc[i] == '.')
                point = i;
            else
                value = value * 10 + cc[i] - '0';
        }

        int divider = 1;
        if (point > -1)
            divider = pow10(length - point - 1);

        return negation * value / divider;
    }

    private static int pow10(int n) {

        int result = 1;
        for (int i=0; i<n; i++)
        {
            result *= 10;
        }

        return result;
    }

}

==============================================

Ditest dengan looping 1 juta kali:
==============================================
    @Test
    public void testPerformance()
    {
        long t1 = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++)
        {
//            Double.valueOf("-12.3456");
            ConversionHelper.stringToDouble("-12.3456");
        }

        long t2 = System.currentTimeMillis();
        System.out.println("Elapsed time = " + (t2 - t1) + " ms");
    }

==============================================

Hasilnya adalah:
- Double.valueof(String): Elapsed time = 344 ms
- ConversionHelper.stringToDouble: Elapsed time = 157 ms

Sori panjang banget :D Thx kalo udah baca smp di sini.
Skr saatnya utk menerima challenge utk mendapatkan hasil yg lebih optimal ;)

regards,
T Budi S