getbits.h (2862B)
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. 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. 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 */