nom.tam.fits.compression.algorithm.quant.RandomSequence Maven / Gradle / Ivy
package nom.tam.fits.compression.algorithm.quant;
/*-
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* nom.tam FITS library
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*/
/**
* A standard fixed random sequence to use for portable and reversible dither
* implementations. This is a modified (improved) version of the random sequence
* implementation in Appendix I of the FITS
* 4.0 standard, using integer arithmetics for better performance -- but
* still providing the same sequence as the original algorithm.
*
* @see QuantizeProcessor
*/
public final class RandomSequence {
/**
* DO NOT CHANGE THIS; used when quantizing real numbers
*/
private static final int N_RANDOM = 10000;
private static final int RANDOM_FACTOR = 16807;
/**
* This is our cached fixed random sequence that we will use over and over,
* but we defer initializing it until we actually need it.
*/
private static final double[] VALUES = new double[N_RANDOM];
/**
* Static initialization for the fixed sequence of random values.
*/
static {
long ival = 1L;
for (int i = 0; i < N_RANDOM; i++) {
ival = (ival * RANDOM_FACTOR) % Integer.MAX_VALUE;
VALUES[i] = (double) ival / Integer.MAX_VALUE;
}
}
/** We don't instantiate this class */
private RandomSequence() {
}
/**
* Returns the ith random value from the sequence
*
* @param i
* The index between 0 and {@link #length()} (exclusive).
* @return The fixed uniform random deviate value at that index in the range
* of 0.0 to 1.0 (exclusive).
* @see #length()
*/
public static double get(int i) {
return VALUES[i];
}
/**
* Returns the number of random values in the sequence.
*
* @return The number of random values available from the fixed sequence.
*/
public static int length() {
return VALUES.length;
}
}