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https://issues.apache.org/jira/browse/MATH-1306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15071336#comment-15071336
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Gilles commented on MATH-1306:
------------------------------
bq. I just don't like scattering a discussion over several places.
Discussions on whether to add a feature must happen on the "dev" ML.
Then a report is opened on the tracking system.
Discussion here are more related to implementation details.
bq. here is the benchmark.
Why do you put the "subArray" allocation inside the loop?
I don't know whether it's significant for the performance for a few iterations
but for many iterations it will indeed allocate much more memory...
Could you please attach the Java files of the benchmark?
> 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
>
> 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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