1 /*
2 * Copyright © 2018, VideoLAN and dav1d authors
3 * Copyright © 2018, Two Orioles, LLC
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright notice, this
10 * list of conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright notice,
13 * this list of conditions and the following disclaimer in the documentation
14 * and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
20 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
22 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
23 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
25 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #ifndef DAV1D_SRC_GETBITS_H
29 #define DAV1D_SRC_GETBITS_H
30
31 #include <stddef.h>
32 #include <stdint.h>
33
34 typedef struct GetBits {
35 uint64_t state;
36 int bits_left, error;
37 const uint8_t *ptr, *ptr_start, *ptr_end;
38 } GetBits;
39
40 void dav1d_init_get_bits(GetBits *c, const uint8_t *data, size_t sz);
41 unsigned dav1d_get_bit(GetBits *c);
42 unsigned dav1d_get_bits(GetBits *c, int n);
43 int dav1d_get_sbits(GetBits *c, int n);
44 unsigned dav1d_get_uleb128(GetBits *c);
45
46 // Output in range 0..max-1
47 unsigned dav1d_get_uniform(GetBits *c, unsigned max);
48 unsigned dav1d_get_vlc(GetBits *c);
49 int dav1d_get_bits_subexp(GetBits *c, int ref, unsigned n);
50
51 // Discard bits from the buffer until we're next byte-aligned.
dav1d_bytealign_get_bits(GetBits * c)52 static inline void dav1d_bytealign_get_bits(GetBits *c) {
53 // bits_left is never more than 7, because it is only incremented
54 // by refill(), called by dav1d_get_bits and that never reads more
55 // than 7 bits more than it needs.
56 //
57 // If this wasn't true, we would need to work out how many bits to
58 // discard (bits_left % 8), subtract that from bits_left and then
59 // shift state right by that amount.
60 assert(c->bits_left <= 7);
61
62 c->bits_left = 0;
63 c->state = 0;
64 }
65
66 // Return the current bit position relative to the start of the buffer.
dav1d_get_bits_pos(const GetBits * c)67 static inline unsigned dav1d_get_bits_pos(const GetBits *c) {
68 return (unsigned) (c->ptr - c->ptr_start) * 8 - c->bits_left;
69 }
70
71 #endif /* DAV1D_SRC_GETBITS_H */
72