[MATH-1305] Improve performance of nextBytes() method of BitsStreamGenerator and AbstractRandomGenerator

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0, 3.5, 3.6
• Fix Version/s: 3.6
• Flags: Patch, Important
• External issue ID: MATH-1300
• Assignee: Unassigned
• Reporter: Rostislav Krasny
• Created: 21/Dec/15 00:43
• Updated: 25/Jan/16 20:27
• Resolved: 31/Dec/15 23:23

Description

I propose to use this code in BitsStreamGenerator

	@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 remains bytes
		if (index < bytes.length) {
			int random = next(32);
			while (true) {
				bytes[index++] = (byte) random;
				if (index < bytes.length) {
					random >>>= 8;
				} else {
					break;
				}
			}
		}
	}

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.

Issue Links

• relates to: MATH-1300 BitsStreamGenerator#nextBytes(byte[]) is wrong