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40
41 package org.h2.compress;
42
43 public class CompressLZF implements Compresser {
44
45 public void setOptions(String  options) {
46 }
47
48 public int getAlgorithm() {
49 return Compresser.LZF;
50 }
51
52 static final int HLOG = 14;
53 static final int HASH_SIZE = (1 << 14);
54 static final int MAX_LITERAL = (1 << 5);
55 static final int MAX_OFF = (1 << 13);
56 static final int MAX_REF = ((1 << 8) + (1 << 3));
57
58 int first(byte[] in, int inPos) {
59 return (in[inPos] << 8) + (in[inPos + 1] & 255);
60 }
61
62 int next(int v, byte[] in, int inPos) {
63 return (v << 8) + (in[inPos + 2] & 255);
64 }
65
66 int hash(int h) {
67 return ((h * 184117) >> 9) & (HASH_SIZE - 1);
69 }
70
71 private int[] hashTab;
72 private static int[] empty = new int[HASH_SIZE];
73
74 public int compress(byte[] in, int inLen, byte[] out, int outPos) {
75 int inPos = 0;
76 if(hashTab == null) {
77 hashTab = new int[HASH_SIZE];
78 } else {
79 System.arraycopy(empty, 0, hashTab, 0, HASH_SIZE);
80 }
81 int literals = 0;
82 int hval = first(in, inPos);
83 while (true) {
84 if (inPos < inLen - 4) {
85 hval = next(hval, in, inPos);
86 int off = hash(hval);
87 int ref = hashTab[off];
88 hashTab[off] = inPos;
89 off = inPos - ref - 1;
90 if (off < MAX_OFF && ref > 0 && in[ref + 2] == in[inPos + 2] && in[ref + 1] == in[inPos + 1] && in[ref] == in[inPos]) {
91 int maxlen = inLen - inPos - 2;
92 maxlen = maxlen > MAX_REF ? MAX_REF : maxlen;
93 int len = 3;
94 while (len < maxlen && in[ref + len] == in[inPos + len]) {
95 len++;
96 }
97 len -= 2;
98 if (literals != 0) {
99 out[outPos++] = (byte) (literals - 1);
100 literals = -literals;
101 do {
102 out[outPos++] = in[inPos + literals++];
103 } while (literals != 0);
104 }
105 if (len < 7) {
106 out[outPos++] = (byte) ((off >> 8) + (len << 5));
107 } else {
108 out[outPos++] = (byte) ((off >> 8) + (7 << 5));
109 out[outPos++] = (byte) (len - 7);
110 }
111 out[outPos++] = (byte) off;
112 inPos += len;
113 hval = first(in, inPos);
114 hval = next(hval, in, inPos);
115 hashTab[hash(hval)] = inPos++;
116 hval = next(hval, in, inPos);
117 hashTab[hash(hval)] = inPos++;
118 continue;
119 }
120 } else if (inPos == inLen) {
121 break;
122 }
123 inPos++;
124 literals++;
125 if (literals == MAX_LITERAL) {
126 out[outPos++] = (byte) (literals - 1);
127 literals = -literals;
128 do {
129 out[outPos++] = in[inPos + literals++];
130 } while (literals != 0);
131 }
132 }
133 if (literals != 0) {
134 out[outPos++] = (byte) (literals - 1);
135 literals = -literals;
136 do {
137 out[outPos++] = in[inPos + literals++];
138 } while (literals != 0);
139 }
140 return outPos;
141 }
142
143 public void expand(byte[] in, int inPos, int inLen, byte[] out, int outPos, int outLen) {
144 do {
145 int ctrl = in[inPos++] & 255;
146 if (ctrl < (1 << 5)) {
147 ctrl += inPos;
149 do {
150 out[outPos++] = in[inPos];
151 } while (inPos++ < ctrl);
152 } else {
153 int len = ctrl >> 5;
155 int ref = -((ctrl & 0x1f) << 8) - 1;
156 if (len == 7) {
157 len += in[inPos++] & 255;
158 }
159 ref -= in[inPos++] & 255;
160 len += outPos + 2;
161 out[outPos] = out[outPos++ + ref];
162 out[outPos] = out[outPos++ + ref];
163 while (outPos < len - 8) {
164 out[outPos] = out[outPos++ + ref];
165 out[outPos] = out[outPos++ + ref];
166 out[outPos] = out[outPos++ + ref];
167 out[outPos] = out[outPos++ + ref];
168 out[outPos] = out[outPos++ + ref];
169 out[outPos] = out[outPos++ + ref];
170 out[outPos] = out[outPos++ + ref];
171 out[outPos] = out[outPos++ + ref];
172 }
173 while (outPos < len) {
174 out[outPos] = out[outPos++ + ref];
175 }
176 }
177 } while (outPos < outLen);
178 }
179 }
180
181
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