Rostislav Krasny created MATH-1306:
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Summary: 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 < bytes.length) {
random >>>= 8;
} else {
break;
}
}
}
}
{code}
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