1 package nom.tam.fits.compression.algorithm.quant;
2
3 /*-
4 * #%L
5 * nom.tam FITS library
6 * %%
7 * Copyright (C) 1996 - 2024 nom-tam-fits
8 * %%
9 * This is free and unencumbered software released into the public domain.
10 *
11 * Anyone is free to copy, modify, publish, use, compile, sell, or
12 * distribute this software, either in source code form or as a compiled
13 * binary, for any purpose, commercial or non-commercial, and by any
14 * means.
15 *
16 * In jurisdictions that recognize copyright laws, the author or authors
17 * of this software dedicate any and all copyright interest in the
18 * software to the public domain. We make this dedication for the benefit
19 * of the public at large and to the detriment of our heirs and
20 * successors. We intend this dedication to be an overt act of
21 * relinquishment in perpetuity of all present and future rights to this
22 * software under copyright law.
23 *
24 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
25 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
26 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
27 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
28 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
29 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
30 * OTHER DEALINGS IN THE SOFTWARE.
31 * #L%
32 */
33
34 /**
35 * A standard fixed random sequence to use for portable and reversible dither
36 * implementations. This is a modified (improved) version of the random sequence
37 * implementation in Appendix I of the <a
38 * href="https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf">FITS
39 * 4.0 standard</a>, using integer arithmetics for better performance -- but
40 * still providing the same sequence as the original algorithm.
41 *
42 * @see QuantizeProcessor
43 */
44 public final class RandomSequence {
45
46 /**
47 * DO NOT CHANGE THIS; used when quantizing real numbers
48 */
49 private static final int N_RANDOM = 10000;
50
51 private static final int RANDOM_FACTOR = 16807;
52
53 /**
54 * This is our cached fixed random sequence that we will use over and over,
55 * but we defer initializing it until we actually need it.
56 */
57 private static final double[] VALUES = new double[N_RANDOM];
58
59 /**
60 * Static initialization for the fixed sequence of random values.
61 */
62 static {
63 long ival = 1L;
64 for (int i = 0; i < N_RANDOM; i++) {
65 ival = (ival * RANDOM_FACTOR) % Integer.MAX_VALUE;
66 VALUES[i] = (double) ival / Integer.MAX_VALUE;
67 }
68 }
69
70 /** We don't instantiate this class */
71 private RandomSequence() {
72 }
73
74 /**
75 * Returns the <i>i</i><sup>th</sup> random value from the sequence
76 *
77 * @param i
78 * The index between 0 and {@link #length()} (exclusive).
79 * @return The fixed uniform random deviate value at that index in the range
80 * of 0.0 to 1.0 (exclusive).
81 * @see #length()
82 */
83 public static double get(int i) {
84 return VALUES[i];
85 }
86
87 /**
88 * Returns the number of random values in the sequence.
89 *
90 * @return The number of random values available from the fixed sequence.
91 */
92 public static int length() {
93 return VALUES.length;
94 }
95 }