[MATH-1306] Add public void nextBytes(byte[] bytes, int position, int length) method into the RandomGenerator interface

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 3.5
• Flags: Patch
• Assignee: Unassigned
• Reporter: Rostislav Krasny
• Created: 23/Dec/15 20:43
• Updated: 04/Feb/16 01:05
• Resolved: 04/Feb/16 01:05

Description

I propose to add public void nextBytes(byte[] bytes, int position, int length) method into the RandomGenerator interface.

Rationality: to improve performance and memory usage in cases when one needs to fill only a specified region of a byte array. Today to do that you need to use a temporary byte array and copy it by yourself into the specified region of the destination byte array.

I propose the following code, based on the code of BitsStreamGenerator commited in MATH-1305

	@Override
	public void nextBytes(byte[] bytes) {
		nextBytesFill(bytes, 0, bytes.length);
	}

	// TODO add this method into RandomGenerator interface
	//@Override
	public void nextBytes(byte[] bytes, int position, int length) {
		if (position < 0 || position > bytes.length - 1) {
			throw new OutOfRangeException(LocalizedFormats.OUT_OF_RANGE_SIMPLE, position, 0, bytes.length - 1);
		}
		if (length < 0 || length > bytes.length - position) {
			throw new OutOfRangeException(LocalizedFormats.OUT_OF_RANGE_SIMPLE, length, 0, bytes.length - position);
		}

		nextBytesFill(bytes, position, length);
	}

	private void nextBytesFill(byte[] bytes, int position, int length) {
		int index = position;

		// Position plus multiple 4 part of length (i.e. length with two least significant bits unset).
		final int indexLoopLimit = position + (length & 0x7ffffffc);

		// Start filling in the byte array, 4 bytes at a time.
		while (index < indexLoopLimit) {
			final int random = next(32);
			bytes[index++] = (byte) random;
			bytes[index++] = (byte) (random >>> 8);
			bytes[index++] = (byte) (random >>> 16);
			bytes[index++] = (byte) (random >>> 24);
		}

		final int indexLimit = position + length;
		
		// Fill in the remaining bytes.
		if (index < indexLimit) {
			int random = next(32);
			while (true) {
				bytes[index++] = (byte) random;
				if (index < indexLimit) {
					random >>>= 8;
				} else {
					break;
				}
			}
		}
	}

Issue Links

• depends upon: MATH-1307 Create a base class for all RNGs
• is superceded by: MATH-1319 Refactor the package "o.a.c.m.random"