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Date: Sun, 27 Dec 2015 22:13:49 +0000 (UTC)
From: "Rostislav Krasny (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Message-ID: <JIRA.12924088.1450903422000.12349.1451254429567@Atlassian.JIRA>
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Subject: [jira] [Comment Edited] (MATH-1306) Add public void
 nextBytes(byte[] bytes, int position, int length) method into the
 RandomGenerator interface
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    [ https://issues.apache.org/jira/browse/MATH-1306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15072260#comment-15072260 ] 

Rostislav Krasny edited comment on MATH-1306 at 12/27/15 10:13 PM:
-------------------------------------------------------------------

{quote}Since the new feature is about reusing the same array to fill different regions of it at different times, why not also keep the small array for reuse?{quote}
This is not about reusing the same array but about having a direct access to the destination array. And reusing the same intermediate array is not always possible or practical. But even without temporary array allocation in each loop iteration the {{System.arraycopy()}} also takes time, although it is a native method.

{quote}Could you please provide a use-case of such a simplification?{quote}
Cryptography. I had seen a cryptographic software that uses a method with a signature similar to the proposed.

{quote}I only see that the signature is more complex; the purpose of Commons Math is not to cover all hypothetical cases.{quote}
This is very common to have methods that work with regions of arrays or collections. The mentioned here {{System.arraycopy()}} or methods of {{java.util.Arrays}} class. And I'm sure this list could be much longer.

I just found the proposed nextByte() method signature already exists in {{gnu.crypto.util.PRNG}} pseudo-random number generator.
[http://www.gnu.org/software/gnu-crypto/manual/api/gnu/crypto/util/PRNG.html]

Also there is a not exact but very similar method signature in {{RandomData.OneShot}} of javacard
[https://docs.oracle.com/javacard/3.0.5/api/javacard/security/RandomData.OneShot.html]#nextBytes%28byte[],%20short,%20short%29

Apache Tomcat has a tricky method with similar functionality just because {{java.util.Random}} doesn't have the proposed method
[https://tomcat.apache.org/tomcat-7.0-doc/api/org/apache/catalina/tribes/util/UUIDGenerator.html]#nextBytes%28byte[],%20int,%20int,%20java.util.Random%29

So why not to add the proposed method signature into CM as well?

P.S. why URLs with # are not supported by Jira?
[https://docs.oracle.com/javacard/3.0.5/api/javacard/security/RandomData.OneShot.html#nextBytes%28byte[],%20short,%20short%29]


was (Author: rosti.bsd):
{quote}Since the new feature is about reusing the same array to fill different regions of it at different times, why not also keep the small array for reuse?{quote}
This is not about reusing the same array but about having a direct access to the destination array. And reusing the same intermediate array is not always possible or practical. But even without temporary array allocation in each loop iteration the {{System.arraycopy()}} also takes time, although it is a native method.

{quote}Could you please provide a use-case of such a simplification?{quote}
Cryptography. I had seen a cryptographic software that uses a method with a signature similar to the proposed.

{quote}I only see that the signature is more complex; the purpose of Commons Math is not to cover all hypothetical cases.{quote}
This is very common to have methods that work with regions of arrays or collections. The mentioned here {{System.arraycopy()}} or methods of {{java.util.Arrays}} class. And I'm sure this list could be much longer.

I just found the proposed nextByte() method signature already exists in {{gnu.crypto.util.PRNG}} pseudo-random number generator.
[http://www.gnu.org/software/gnu-crypto/manual/api/gnu/crypto/util/PRNG.html]

Also there is a not exact but very similar method signature in {{RandomData.OneShot}} of javacard
[https://docs.oracle.com/javacard/3.0.5/api/javacard/security/RandomData.OneShot.html]#nextBytes%28byte[],%20short,%20short%29

Apache Tomcat has a tricky method with similar functionality just because {{java.lang.Random}} doesn't have the proposed method
[https://tomcat.apache.org/tomcat-7.0-doc/api/org/apache/catalina/tribes/util/UUIDGenerator.html]#nextBytes%28byte[],%20int,%20int,%20java.util.Random%29

So why not to add the proposed method signature into CM as well?

P.S. why URLs with # are not supported by Jira?
[https://docs.oracle.com/javacard/3.0.5/api/javacard/security/RandomData.OneShot.html#nextBytes%28byte[],%20short,%20short%29]

> Add public void nextBytes(byte[] bytes, int position, int length) method into the RandomGenerator interface
> -----------------------------------------------------------------------------------------------------------
>
>                 Key: MATH-1306
>                 URL: https://issues.apache.org/jira/browse/MATH-1306
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.5
>            Reporter: Rostislav Krasny
>         Attachments: MersenneTwister1305.java, MersenneTwister1306.java
>
>
> 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
> {code:java}
> 	@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;
> 				}
> 			}
> 		}
> 	}
> {code}


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