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authorBjörn Stenberg <bjorn@haxx.se>2007-01-08 23:53:00 +0000
committerBjörn Stenberg <bjorn@haxx.se>2007-01-08 23:53:00 +0000
commit7039a05147b8bbfc829babea1c65bd436450b505 (patch)
tree4ba555eb84ed97b72b0575034d5b0530a393713e /songdbj/javazoom/jl/decoder/BitReserve.java
parent6d4c19707ef95942e323cbdc89fbbfdbe45e7cc5 (diff)
downloadrockbox-7039a05147b8bbfc829babea1c65bd436450b505.tar.gz
rockbox-7039a05147b8bbfc829babea1c65bd436450b505.zip
Splitting out songdbj
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@11953 a1c6a512-1295-4272-9138-f99709370657
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1/*
2 * 11/19/04 1.0 moved to LGPL.
3 *
4 * 12/12/99 0.0.7 Implementation stores single bits
5 * as ints for better performance. mdm@techie.com.
6 *
7 * 02/28/99 0.0 Java Conversion by E.B, javalayer@javazoom.net
8 *
9 * Adapted from the public c code by Jeff Tsay.
10 *
11 *-----------------------------------------------------------------------
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as published
14 * by the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
21 *
22 * You should have received a copy of the GNU Library General Public
23 * License along with this program; if not, write to the Free Software
24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
25 *----------------------------------------------------------------------
26 */
27
28package javazoom.jl.decoder;
29
30/**
31 * Implementation of Bit Reservoir for Layer III.
32 * <p>
33 * The implementation stores single bits as a word in the buffer. If
34 * a bit is set, the corresponding word in the buffer will be non-zero.
35 * If a bit is clear, the corresponding word is zero. Although this
36 * may seem waseful, this can be a factor of two quicker than
37 * packing 8 bits to a byte and extracting.
38 * <p>
39 */
40
41// REVIEW: there is no range checking, so buffer underflow or overflow
42// can silently occur.
43final class BitReserve
44{
45 /**
46 * Size of the internal buffer to store the reserved bits.
47 * Must be a power of 2. And x8, as each bit is stored as a single
48 * entry.
49 */
50 private static final int BUFSIZE = 4096*8;
51
52 /**
53 * Mask that can be used to quickly implement the
54 * modulus operation on BUFSIZE.
55 */
56 private static final int BUFSIZE_MASK = BUFSIZE-1;
57
58 private int offset, totbit, buf_byte_idx;
59 private final int[] buf = new int[BUFSIZE];
60 private int buf_bit_idx;
61
62 BitReserve()
63 {
64
65 offset = 0;
66 totbit = 0;
67 buf_byte_idx = 0;
68 }
69
70
71 /**
72 * Return totbit Field.
73 */
74 public int hsstell()
75 {
76 return(totbit);
77 }
78
79 /**
80 * Read a number bits from the bit stream.
81 * @param N the number of
82 */
83 public int hgetbits(int N)
84 {
85 totbit += N;
86
87 int val = 0;
88
89 int pos = buf_byte_idx;
90 if (pos+N < BUFSIZE)
91 {
92 while (N-- > 0)
93 {
94 val <<= 1;
95 val |= ((buf[pos++]!=0) ? 1 : 0);
96 }
97 }
98 else
99 {
100 while (N-- > 0)
101 {
102 val <<= 1;
103 val |= ((buf[pos]!=0) ? 1 : 0);
104 pos = (pos+1) & BUFSIZE_MASK;
105 }
106 }
107 buf_byte_idx = pos;
108 return val;
109 }
110
111
112
113 /**
114 * Read 1 bit from the bit stream.
115 */
116/*
117 public int hget1bit_old()
118 {
119 int val;
120 totbit++;
121 if (buf_bit_idx == 0)
122 {
123 buf_bit_idx = 8;
124 buf_byte_idx++;
125 }
126 // BUFSIZE = 4096 = 2^12, so
127 // buf_byte_idx%BUFSIZE == buf_byte_idx & 0xfff
128 val = buf[buf_byte_idx & BUFSIZE_MASK] & putmask[buf_bit_idx];
129 buf_bit_idx--;
130 val = val >>> buf_bit_idx;
131 return val;
132 }
133 */
134 /**
135 * Returns next bit from reserve.
136 * @returns 0 if next bit is reset, or 1 if next bit is set.
137 */
138 public int hget1bit()
139 {
140 totbit++;
141 int val = buf[buf_byte_idx];
142 buf_byte_idx = (buf_byte_idx+1) & BUFSIZE_MASK;
143 return val;
144 }
145
146 /**
147 * Retrieves bits from the reserve.
148 */
149/*
150 public int readBits(int[] out, int len)
151 {
152 if (buf_bit_idx == 0)
153 {
154 buf_bit_idx = 8;
155 buf_byte_idx++;
156 current = buf[buf_byte_idx & BUFSIZE_MASK];
157 }
158
159
160
161 // save total number of bits returned
162 len = buf_bit_idx;
163 buf_bit_idx = 0;
164
165 int b = current;
166 int count = len-1;
167
168 while (count >= 0)
169 {
170 out[count--] = (b & 0x1);
171 b >>>= 1;
172 }
173
174 totbit += len;
175 return len;
176 }
177 */
178
179 /**
180 * Write 8 bits into the bit stream.
181 */
182 public void hputbuf(int val)
183 {
184 int ofs = offset;
185 buf[ofs++] = val & 0x80;
186 buf[ofs++] = val & 0x40;
187 buf[ofs++] = val & 0x20;
188 buf[ofs++] = val & 0x10;
189 buf[ofs++] = val & 0x08;
190 buf[ofs++] = val & 0x04;
191 buf[ofs++] = val & 0x02;
192 buf[ofs++] = val & 0x01;
193
194 if (ofs==BUFSIZE)
195 offset = 0;
196 else
197 offset = ofs;
198
199 }
200
201 /**
202 * Rewind N bits in Stream.
203 */
204 public void rewindNbits(int N)
205 {
206 totbit -= N;
207 buf_byte_idx -= N;
208 if (buf_byte_idx<0)
209 buf_byte_idx += BUFSIZE;
210 }
211
212 /**
213 * Rewind N bytes in Stream.
214 */
215 public void rewindNbytes(int N)
216 {
217 int bits = (N << 3);
218 totbit -= bits;
219 buf_byte_idx -= bits;
220 if (buf_byte_idx<0)
221 buf_byte_idx += BUFSIZE;
222 }
223}
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