JavaFastPFOR/src/main/java/me/lemire/longcompression/differential/LongDelta.java at 7f2f5fcdf074bc7c5d1c32119d5d32f0320ed34b · lifeinwild/JavaFastPFOR · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
/**
 * This code is released under the
 * Apache License Version 2.0 http://www.apache.org/licenses/.
 *
 * (c) Daniel Lemire, http://lemire.me/en/
 */

package me.lemire.longcompression.differential;

/**
 * Generic class to compute differential coding.
 *
 * @author Benoit lacelle
 *
 */
public final class LongDelta {

        /**
         * Apply differential coding (in-place).
         *
         * @param data
         *                data to be modified
         */
        public static void delta(long[] data) {
                for (int i = data.length - 1; i > 0; --i) {
                        data[i] -= data[i - 1];
                }
        }

        /**
         * Apply differential coding (in-place) given an initial value.
         *
         * @param data
         *                data to be modified
         * @param start
         *                starting index
         * @param length
         *                number of integers to process
         * @param init
         *                initial value
         * @return next initial vale
         */
        public static long delta(long[] data, int start, int length, int init) {
                final long nextinit = data[start + length - 1];
                for (int i = length - 1; i > 0; --i) {
                        data[start + i] -= data[start + i - 1];
                }
                data[start] -= init;
                return nextinit;
        }

        /**
         * Compute differential coding given an initial value. Output is written
         * to a provided array: must have length "length" or better.
         *
         * @param data
         *                data to be modified
         * @param start
         *                starting index
         * @param length
         *                number of integers to process
         * @param init
         *                initial value
         * @param out
         *                output array
         * @return next initial vale
         */
        public static long delta(long[] data, int start, int length, int init,
                long[] out) {
                for (int i = length - 1; i > 0; --i) {
                        out[i] = data[start + i] - data[start + i - 1];
                }
                out[0] = data[start] - init;
                return data[start + length - 1];
        }

        /**
         * Undo differential coding (in-place). Effectively computes a prefix
         * sum.
         *
         * @param data
         *                to be modified.
         */
        public static void inverseDelta(long[] data) {
                for (int i = 1; i < data.length; ++i) {
                        data[i] += data[i - 1];
                }
        }

        /**
         * Undo differential coding (in-place). Effectively computes a prefix
         * sum. Like inverseDelta, only faster.
         *
         * @param data
         *                to be modified
         */
        public static void fastinverseDelta(long[] data) {
                int sz0 = data.length / 4 * 4;
                int i = 1;
                if (sz0 >= 4) {
                        long a = data[0];
                        for (; i < sz0 - 4; i += 4) {
                                a = data[i] += a;
                                a = data[i + 1] += a;
                                a = data[i + 2] += a;
                                a = data[i + 3] += a;
                        }
                }

                for (; i < data.length; ++i) {
                        data[i] += data[i - 1];
                }
        }

        /**
         * Undo differential coding (in-place). Effectively computes a prefix
         * sum. Like inverseDelta, only faster. Uses an initial value.
         *
         * @param data
         *                to be modified
         * @param start
         *                starting index
         * @param length
         *                number of integers to process
         * @param init
         *                initial value
         * @return next initial value
         */
        public static long fastinverseDelta(long[] data, int start, int length,
                int init) {
                data[start] += init;
                int sz0 = length / 4 * 4;
                int i = 1;
                if (sz0 >= 4) {
                    long a = data[start];
                        for (; i < sz0 - 4; i += 4) {
                                a = data[start + i] += a;
                                a = data[start + i + 1] += a;
                                a = data[start + i + 2] += a;
                                a = data[start + i + 3] += a;
                        }
                }

                for (; i != length; ++i) {
                        data[start + i] += data[start + i - 1];
                }
                return data[start + length - 1];
        }

}