Simplify get_bits1().
[paraslash.git] / bitstream.h
1 /*
2 * Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.h.
3 *
4 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
5 *
6 * Licensed under the GNU Lesser General Public License.
7 * For licencing details see COPYING.LIB.
8 */
9
10 /** \file bitstream.h Bitstream structures and inline functions. */
11
12 #define AV_RB32(x) ((((const uint8_t*)(x))[0] << 24) | \
13 (((const uint8_t*)(x))[1] << 16) | \
14 (((const uint8_t*)(x))[2] << 8) | \
15 ((const uint8_t*)(x))[3])
16
17 /** Structure for bistream I/O. */
18 struct getbit_context {
19 /* Start of the internal buffer. */
20 const uint8_t *buffer;
21 /* End of the internal buffer. */
22 const uint8_t *buffer_end;
23 /** Bit counter. */
24 int index;
25 };
26
27 #define VLC_TYPE int16_t
28
29 struct vlc {
30 int bits;
31 VLC_TYPE(*table)[2]; ///< code, bits
32 int table_size, table_allocated;
33 };
34
35 static inline uint32_t show_bits(struct getbit_context *gbc, int num)
36 {
37 int idx = gbc->index;
38 uint32_t x = AV_RB32(gbc->buffer + (idx >> 3)) << (idx & 7);
39 return x >> (32 - num);
40 }
41
42 static inline int get_bits_count(struct getbit_context *gbc)
43 {
44 return gbc->index;
45 }
46
47 static inline void skip_bits(struct getbit_context *gbc, int n)
48 {
49 gbc->index += n;
50 }
51
52 static inline unsigned int get_bits(struct getbit_context *gbc, int n)
53 {
54 unsigned int ret = show_bits(gbc, n);
55 skip_bits(gbc, n);
56 return ret;
57 }
58
59 /* This is rather hot, we can do better than get_bits(gbc, 1). */
60 static inline unsigned int get_bits1(struct getbit_context *gbc)
61 {
62 int idx = gbc->index++;
63 uint8_t tmp = gbc->buffer[idx >> 3], mask = (1 << (7 - (idx & 7)));
64 return !!(tmp & mask);
65 }
66
67 /**
68 * Initialize a getbit_context structure.
69 *
70 * \param buffer The bitstream buffer. It must be FF_INPUT_BUFFER_PADDING_SIZE
71 * bytes larger then the actual read bits * because some optimized bitstream
72 * readers read 32 or 64 bit at once and could read over the end.
73 *
74 * \param bit_size The size of the buffer in bytes.
75 */
76 static inline void init_get_bits(struct getbit_context *gbc,
77 const uint8_t *buffer, int size)
78 {
79 gbc->buffer = buffer;
80 gbc->buffer_end = buffer + size;
81 gbc->index = 0;
82 }
83
84 void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
85 const void *codes, int codes_size);
86
87 void free_vlc(struct vlc *vlc);
88
89 /**
90 * Parse a vlc code.
91 *
92 * \param bits The number of bits which will be read at once, must be
93 * identical to nb_bits in init_vlc()
94 *
95 * \param max_depth The number of times bits bits must be read to completely
96 * read the longest vlc code = (max_vlc_length + bits - 1) / bits.
97 */
98 static inline int get_vlc(struct getbit_context *gbc, VLC_TYPE(*table)[2],
99 int bits, int max_depth)
100 {
101 int n, idx, nb_bits, code;
102
103 idx = show_bits(gbc, bits);
104 code = table[idx][0];
105 n = table[idx][1];
106 if (max_depth > 1 && n < 0) {
107 skip_bits(gbc, bits);
108 nb_bits = -n;
109 idx = show_bits(gbc, nb_bits) + code;
110 code = table[idx][0];
111 n = table[idx][1];
112 if (max_depth > 2 && n < 0) {
113 skip_bits(gbc, nb_bits);
114 nb_bits = -n;
115 idx = show_bits(gbc, nb_bits) + code;
116 code = table[idx][0];
117 n = table[idx][1];
118 }
119 }
120 skip_bits(gbc, n);
121 return code;
122 }