From dd3d7ddf2a508b15877bb978c2309f777853a228 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alexandra=20H=C3=A1jkov=C3=A1?= Date: Fri, 22 Apr 2016 09:43:52 +0200 Subject: [PATCH] lavc: add a new bitstream reader to replace get_bits The new bit reader features a simpler API and an implementation without stacks of nested macros. Signed-off-by: Anton Khirnov --- libavcodec/bitstream.h | 387 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 387 insertions(+) create mode 100644 libavcodec/bitstream.h diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h new file mode 100644 index 0000000000..996e32e83b --- /dev/null +++ b/libavcodec/bitstream.h @@ -0,0 +1,387 @@ +/* + * Copyright (c) 2016 Alexandra Hájková + * + * This file is part of Libav. + * + * Libav is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * Libav is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with Libav; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/** + * @file + * functions for reading bits from a buffer + */ + +#ifndef AVCODEC_BITSTREAM_H +#define AVCODEC_BITSTREAM_H + +#include + +#include "libavutil/common.h" +#include "libavutil/intreadwrite.h" +#include "libavutil/log.h" + +#include "mathops.h" +#include "vlc.h" + +typedef struct BitstreamContext { + uint64_t bits; // stores bits read from the buffer + const uint8_t *buffer, *buffer_end; + const uint8_t *ptr; // position inside a buffer + unsigned bits_left; // number of bits left in bits field + unsigned size_in_bits; +} BitstreamContext; + +static inline void refill_64(BitstreamContext *bc) +{ + if (bc->ptr >= bc->buffer_end) + return; + +#ifdef BITSTREAM_READER_LE + bc->bits = AV_RL64(bc->ptr); +#else + bc->bits = AV_RB64(bc->ptr); +#endif + bc->ptr += 8; + bc->bits_left = 64; +} + +static inline void refill_32(BitstreamContext *bc) +{ + if (bc->ptr >= bc->buffer_end) + return; + +#ifdef BITSTREAM_READER_LE + bc->bits = (uint64_t)AV_RL32(bc->ptr) << bc->bits_left | bc->bits; +#else + bc->bits = bc->bits | (uint64_t)AV_RB32(bc->ptr) << (32 - bc->bits_left); +#endif + bc->ptr += 4; + bc->bits_left += 32; +} + +/* Initialize BitstreamContext. Input buffer must have an additional zero + * padding of AV_INPUT_BUFFER_PADDING_SIZE bytes at the end. */ +static inline int bitstream_init(BitstreamContext *bc, const uint8_t *buffer, + unsigned bit_size) +{ + unsigned buffer_size; + + if (bit_size > INT_MAX - 7 || !buffer) { + buffer = + bc->buffer = + bc->ptr = NULL; + bc->bits_left = 0; + return AVERROR_INVALIDDATA; + } + + buffer_size = (bit_size + 7) >> 3; + + bc->buffer = buffer; + bc->buffer_end = buffer + buffer_size; + bc->ptr = bc->buffer; + bc->size_in_bits = bit_size; + bc->bits_left = 0; + bc->bits = 0; + + refill_64(bc); + + return 0; +} + +/* Initialize BitstreamContext with buffer size in bytes instead of bits. */ +static inline int bitstream_init8(BitstreamContext *bc, const uint8_t *buffer, + unsigned byte_size) +{ + if (byte_size > INT_MAX / 8) + return AVERROR_INVALIDDATA; + return bitstream_init(bc, buffer, byte_size * 8); +} + +/* Return number of bits already read. */ +static inline int bitstream_tell(const BitstreamContext *bc) +{ + return (bc->ptr - bc->buffer) * 8 - bc->bits_left; +} + +/* Return buffer size in bits. */ +static inline int bitstream_tell_size(const BitstreamContext *bc) +{ + return bc->size_in_bits; +} + +/* Return the number of the bits left in a buffer. */ +static inline int bitstream_bits_left(const BitstreamContext *bc) +{ + return (bc->buffer - bc->ptr) * 8 + bc->size_in_bits + bc->bits_left; +} + +static inline uint64_t get_val(BitstreamContext *bc, unsigned n) +{ +#ifdef BITSTREAM_READER_LE + uint64_t ret = bc->bits & ((UINT64_C(1) << n) - 1); + bc->bits >>= n; +#else + uint64_t ret = bc->bits >> (64 - n); + bc->bits <<= n; +#endif + bc->bits_left -= n; + + return ret; +} + +/* Return one bit from the buffer. */ +static inline unsigned bitstream_read_bit(BitstreamContext *bc) +{ + if (!bc->bits_left) + refill_64(bc); + + return get_val(bc, 1); +} + +/* Return n bits from the buffer. n has to be in the 0-63 range. */ +static inline uint64_t bitstream_read_63(BitstreamContext *bc, unsigned n) +{ + uint64_t ret = 0; +#ifdef BITSTREAM_READER_LE + uint64_t left = 0; +#endif + + if (!n) + return 0; + + if (n > bc->bits_left) { + n -= bc->bits_left; +#ifdef BITSTREAM_READER_LE + left = bc->bits_left; +#endif + ret = get_val(bc, bc->bits_left); + refill_64(bc); + } + +#ifdef BITSTREAM_READER_LE + ret = get_val(bc, n) << left | ret; +#else + ret = get_val(bc, n) | ret << n; +#endif + + return ret; +} + +/* Return n bits from the buffer. n has to be in the 0-32 range. */ +static inline uint32_t bitstream_read(BitstreamContext *bc, unsigned n) +{ + if (!n) + return 0; + + if (n > bc->bits_left) { + refill_32(bc); + if (bc->bits_left < 32) + bc->bits_left = n; + } + + return get_val(bc, n); +} + +/* Return n bits from the buffer as a signed integer. + * n has to be in the 0-32 range. */ +static inline int32_t bitstream_read_signed(BitstreamContext *bc, unsigned n) +{ + return sign_extend(bitstream_read(bc, n), n); +} + +static inline unsigned show_val(const BitstreamContext *bc, unsigned n) +{ +#ifdef BITSTREAM_READER_LE + return bc->bits & ((UINT64_C(1) << n) - 1); +#else + return bc->bits >> (64 - n); +#endif +} + +/* Return n bits from the buffer, but do not change the buffer state. + * n has to be in the 0-32 range. */ +static inline unsigned bitstream_peek(BitstreamContext *bc, unsigned n) +{ + if (n > bc->bits_left) + refill_32(bc); + + return show_val(bc, n); +} + +/* Return n bits from the buffer as a signed integer, but do not change the + * buffer state. n has to be in the 0-32 range. */ +static inline int bitstream_peek_signed(BitstreamContext *bc, unsigned n) +{ + return sign_extend(bitstream_peek(bc, n), n); +} + +static inline void skip_remaining(BitstreamContext *bc, unsigned n) +{ +#ifdef BITSTREAM_READER_LE + bc->bits >>= n; +#else + bc->bits <<= n; +#endif + bc->bits_left -= n; +} + +/* Skip n bits in the buffer. */ +static inline void bitstream_skip(BitstreamContext *bc, unsigned n) +{ + if (n <= bc->bits_left) + skip_remaining(bc, n); + else { + n -= bc->bits_left; + skip_remaining(bc, bc->bits_left); + if (n >= 64) { + unsigned skip = n / 8; + + n -= skip * 8; + bc->ptr += skip; + } + refill_64(bc); + if (n) + skip_remaining(bc, n); + } +} + +/* Seek to the given bit position. */ +static inline void bitstream_seek(BitstreamContext *bc, unsigned pos) +{ + bc->ptr = bc->buffer; + bc->bits = 0; + bc->bits_left = 0; + + bitstream_skip(bc, pos); +} + +/* Skip bits to a byte boundary. */ +static inline const uint8_t *bitstream_align(BitstreamContext *bc) +{ + unsigned n = -bitstream_tell(bc) & 7; + if (n) + bitstream_skip(bc, n); + return bc->buffer + (bitstream_tell(bc) >> 3); +} + +/* Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB). + * If MSB not set it is negative. */ +static inline int bitstream_read_xbits(BitstreamContext *bc, unsigned length) +{ + int32_t cache = bitstream_peek(bc, 32); + int sign = ~cache >> 31; + skip_remaining(bc, length); + + return ((((uint32_t)(sign ^ cache)) >> (32 - length)) ^ sign) - sign; +} + +/* Return the LUT element for the given bitstream configuration. */ +static inline int set_idx(BitstreamContext *bc, int code, int *n, int *nb_bits, + VLC_TYPE (*table)[2]) +{ + unsigned idx; + + *nb_bits = -*n; + idx = bitstream_peek(bc, *nb_bits) + code; + *n = table[idx][1]; + + return table[idx][0]; +} + +/** + * Parse a VLC code. + * @param bits is the number of bits which will be read at once, must be + * identical to nb_bits in init_vlc() + * @param max_depth is the number of times bits bits must be read to completely + * read the longest VLC code + * = (max_vlc_length + bits - 1) / bits + * If the VLC code is invalid and max_depth = 1, then no bits will be removed. + * If the VLC code is invalid and max_depth > 1, then the number of bits removed + * is undefined. */ +static inline int bitstream_read_vlc(BitstreamContext *bc, VLC_TYPE (*table)[2], + int bits, int max_depth) +{ + int nb_bits; + unsigned idx = bitstream_peek(bc, bits); + int code = table[idx][0]; + int n = table[idx][1]; + + if (max_depth > 1 && n < 0) { + skip_remaining(bc, bits); + code = set_idx(bc, code, &n, &nb_bits, table); + if (max_depth > 2 && n < 0) { + skip_remaining(bc, nb_bits); + code = set_idx(bc, code, &n, &nb_bits, table); + } + } + skip_remaining(bc, n); + + return code; +} + +#define BITSTREAM_RL_VLC(level, run, bc, table, bits, max_depth) \ + do { \ + int n, nb_bits; \ + unsigned index = bitstream_peek(bc, bits); \ + level = table[index].level; \ + n = table[index].len; \ + \ + if (max_depth > 1 && n < 0) { \ + bitstream_skip(bc, bits); \ + \ + nb_bits = -n; \ + \ + index = bitstream_peek(bc, nb_bits) + level; \ + level = table[index].level; \ + n = table[index].len; \ + if (max_depth > 2 && n < 0) { \ + bitstream_skip(bc, nb_bits); \ + nb_bits = -n; \ + \ + index = bitstream_peek(bc, nb_bits) + level; \ + level = table[index].level; \ + n = table[index].len; \ + } \ + } \ + run = table[index].run; \ + bitstream_skip(bc, n); \ + } while (0) + +/* Return decoded truncated unary code for the values 0, 1, 2. */ +static inline int bitstream_decode012(BitstreamContext *bc) +{ + if (!bitstream_read_bit(bc)) + return 0; + else + return bitstream_read_bit(bc) + 1; +} + +/* Return decoded truncated unary code for the values 2, 1, 0. */ +static inline int bitstream_decode210(BitstreamContext *bc) +{ + if (bitstream_read_bit(bc)) + return 0; + else + return 2 - bitstream_read_bit(bc); +} + +/* Read sign bit and flip the sign of the provided value accordingly. */ +static inline int bitstream_apply_sign(BitstreamContext *bc, int val) +{ + int sign = bitstream_read_signed(bc, 1); + return (val ^ sign) - sign; +} + +#endif /* AVCODEC_BITSTREAM_H */