test math and string versions of long truncation

LongNumberTruncate.java

public class LongNumberTruncate {

    public static void main(String[] args) {
        long[] values = new long[8];
        values[0] = 1234567891234567891L; // 16
        values[1] = 123456789223456789L; // 15
        values[2] = 123456789323456L; // 14
        values[3] = 1234567894236L;   // 13
        values[4] = 1234567895L;      // 10

        values[5] = 123456789L; // 9
        values[6] = 1234567L;   // 7
        values[7] = 12345L;   // 5


        for (long value : values) {
            long time;
            long nv;

            time = System.nanoTime();
            nv = base10ByMath(value);
            time = System.nanoTime() - time;
            print("match ", time, value, nv);
            // --------------------------
            time = System.nanoTime();
            nv = base10ByString(value);
            time = System.nanoTime() - time;
            print("string", time, value, nv);
        }

    }

    private static void print(String prefix, long time, long value, long nv) {
        System.out.println(String.format(
                "%s -> %s\n"+
                "orig (%s): %s\n"+
                "new  (%s): %s\n",
                prefix, time,
                String.valueOf(value).length(), value,
                String.valueOf(nv).length(), nv
        ));
    }

    private static final int lbs = 10;
    private static long base10ByString(long x) {
        String value = String.valueOf(x);
        if(value.length()<lbs) {
            int diff = lbs-value.length();
            for(int i=0; i<diff;i++) {
                value += 0;
            }
            return Long.valueOf(value);
        }
        value = value.substring(0,lbs);
        return Long.valueOf(value);
    }

    private static final long base = 1000000000L;
    private static final int lb = (int)Math.ceil(Math.log10(base))+1;
    private static long base10ByMath(long x) {
        if(x<0) {
            return base;
        }
        int l = (int) Math.ceil(Math.log10(x));
        long pow;
        if(l<lb) {
            pow = lb - l;
            return (long) (x * Math.pow(10, pow));
        } else {
            pow =  (long) Math.pow(10, l - lb);
            return x / pow;
        }
    }

    /*
        match  -> 8086
        orig (19): 1234567891234567891
        new  (10): 1234567891

        string -> 35455
        orig (19): 1234567891234567891
        new  (10): 1234567891

        match  -> 4354
        orig (18): 123456789223456789
        new  (10): 1234567892

        string -> 9019
        orig (18): 123456789223456789
        new  (10): 1234567892

        match  -> 1865
        orig (15): 123456789323456
        new  (10): 1234567893

        string -> 9019
        orig (15): 123456789323456
        new  (10): 1234567893

        match  -> 2488
        orig (13): 1234567894236
        new  (10): 1234567894

        string -> 9641
        orig (13): 1234567894236
        new  (10): 1234567894

        match  -> 2488
        orig (10): 1234567895
        new  (10): 1234567895

        string -> 8086
        orig (10): 1234567895
        new  (10): 1234567895

        match  -> 2177
        orig (9): 123456789
        new  (10): 1234567890

        string -> 77440
        orig (9): 123456789
        new  (10): 1234567890

        match  -> 2177
        orig (7): 1234567
        new  (10): 1234567000

        string -> 10885
        orig (7): 1234567
        new  (10): 1234567000

        match  -> 1866
        orig (5): 12345
        new  (10): 1234500000

        string -> 11818
        orig (5): 12345
        new  (10): 1234500000
     */
}