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From "Rostislav Krasny (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MATH-1305) Improve performance nextBytea() method of BitsStreamGenerator and AbstractRandomGenerator
Date Mon, 21 Dec 2015 00:43:46 GMT
Rostislav Krasny created MATH-1305:
--------------------------------------

             Summary: Improve performance nextBytea() method of BitsStreamGenerator and AbstractRandomGenerator

                 Key: MATH-1305
                 URL: https://issues.apache.org/jira/browse/MATH-1305
             Project: Commons Math
          Issue Type: Improvement
    Affects Versions: 3.5, 4.0, 3.6
            Reporter: Rostislav Krasny


I propose to use this code in BitsStreamGenerator
{code:java}
	@Override
	public void nextBytes(byte[] bytes) {
		int index = 0;

		// multiple 4 part of length, i.e length with two least significant bits unset
		int max = bytes.length & 0x7ffffffc;

		// start filling the byte array with tetrads of bytes
		while (index < max) {
			int random = next(32);
			bytes[index++] = (byte) random;
			bytes[index++] = (byte) (random >>> 8);
			bytes[index++] = (byte) (random >>> 16);
			bytes[index++] = (byte) (random >>> 24);
		}

		// fill the reminded bytes
		if (index < bytes.length) {
			int random = next(32);
			while (true) {
				bytes[index++] = (byte) random;
				if (index < bytes.length) {
					random >>>= 8;
				} else {
					break;
				}
			}
		}
	}
{code}
I also propose to use the same code but with nextInt() calls instead of next(32) in the AbstractRandomGenerator.
This implementation improves performance and fixes inconsistency bugs in those two classes
discussed in the MATH-1300. It is also quite simple and well commented.



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