Re: Optimizing Java method

On Jul 11, 12:19 am, Benjamin White <bjwhite66...@yahoo.dummy.com>
wrote:


Have you actually measured how fast this method runs?

I ask, because I just created a (crude) test program to call it and
its fast - I had to measure in nanoseconds to actually get any
timings.

Sure we can make it faster - but do we need to?

Before optimising, you really need to profile using a good profiler -
not a developers guess. Its often the case that we optimise the wrong
parts of the system and the real bottle neck is left untreated.

Anyway...here's the timing I get on a P4 3Ghz 512 ram Windows PC.

Input: 12345.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 35, 69, 12,
Time to convert: 154164ns
Input: -12345.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 35, 69, 13,
Time to convert: 18028ns
Input: 9,876,543.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, -121, 101, 67, 12,
Time to convert: 22296ns
Input: 1 2345.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 35, 69, 12,
Time to convert: 22818ns
Input: $12345.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 35, 69, 12,
Time to convert: 17084ns
Input: -$1 2345.0
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 35, 69, 13,
Time to convert: 15455ns

Here's the class I created which has a copy & paste of your method 'as
is'.

package com.amd.sandbox;

public class StringConverter {
  /**
   * Converts String to packed decimal number. Decimal points, commas
and spaces
   * are ignored. Sign character is processed. Avoid multiple signs.
Characters
   * other than digits are invalid and will cause DataException.
Comma, blank,
   * period, dollar sign and plus are ignored. Scaling and exponents
are not
   * valid.
   *
   * @param str
   * String of number to convert
   * @return byte array of packed decimal, 16 long
   */
  public static byte[] stringToPack(String str) throws Exception {
    int i; // string index
    int j; // byte array index
    boolean nibble_ordinal = false;
    char ch1;
    byte nibble;
    int strlen = str.length();
    byte[] pknum = new byte[16];
    for (i = 0; i < 16; i++) { // initialize to zero
      pknum[i] = 0;
    }
    i = strlen - 1;
    j = 15; /* byte index */
    pknum[j] = 12; // start with positive sign
    while (i > -1) {
      ch1 = str.charAt(i);
      switch (ch1) {
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
        nibble = (byte) Character.getNumericValue(ch1);
        if (nibble_ordinal) {
          pknum[j] = (byte) (pknum[j] | nibble);
          nibble_ordinal ^= true;
        } else {
          pknum[j] = (byte) (pknum[j] | nibble << 4);
          nibble_ordinal ^= true;
          --j;
        }
        --i; // get next char
        break;
      case ',':
      case ' ':
      case '.':
      case '$':
      case '+':
        --i; // get next char
        break;
      case '-':
        pknum[15] = (byte) (pknum[15] & 0xf0);
        pknum[15] = (byte) (pknum[15] | 0x0d);
        --i; // get next char
        break;
      default:
        throw new Exception("Invalid decimal digit: " + ch1);
      }
    }
    return (pknum);
  }

  public static void main(String[] args) throws Exception {
    testWith("12345.0");
    testWith("-12345.0");
    testWith("9,876,543.0");
    testWith("1 2345.0");
    testWith("$12345.0");
    testWith("-$1 2345.0");
  }

  private static void testWith(String inputString) throws Exception {
    System.out.println("Input: " + inputString);

    long startTime = System.nanoTime();
    byte[] answer = stringToPack(inputString);
    long endTime = System.nanoTime();

    for (int i = 0; i < answer.length; i++) {
      System.out.print(answer[i] + ", ");
    }
    System.out.println("\nTime to convert: " + (endTime - startTime)
+"ns");
  }
}