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+/*
+ * Copyright (c) 2016 Alexandra Hájková
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * bitstream reader API header.
+ */
+
+#ifndef AVCODEC_BITSTREAM_H
+#define AVCODEC_BITSTREAM_H
+
+#include <stdint.h>
+
+#include "config.h"
+
+#include "libavutil/avassert.h"
+#include "libavutil/common.h"
+#include "libavutil/intreadwrite.h"
+#include "libavutil/log.h"
+
+#include "mathops.h"
+#include "vlc.h"
+
+#ifndef UNCHECKED_BITSTREAM_READER
+#define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
+#endif
+
+typedef struct BitstreamContext {
+ uint64_t bits; // stores bits read from the buffer
+ const uint8_t *buffer, *buffer_end;
+ const uint8_t *ptr; // pointer to the position inside a buffer
+ unsigned bits_valid; // number of bits left in bits field
+ unsigned size_in_bits;
+} BitstreamContext;
+
+/**
+ * @return
+ * - 0 on successful refill
+ * - a negative number when bitstream end is hit
+ *
+ * Always succeeds when UNCHECKED_BITSTREAM_READER is enabled.
+ */
+static inline int bits_priv_refill_64(BitstreamContext *bc)
+{
+#if !UNCHECKED_BITSTREAM_READER
+ if (bc->ptr >= bc->buffer_end)
+ return -1;
+#endif
+
+#ifdef BITSTREAM_READER_LE
+ bc->bits = AV_RL64(bc->ptr);
+#else
+ bc->bits = AV_RB64(bc->ptr);
+#endif
+ bc->ptr += 8;
+ bc->bits_valid = 64;
+
+ return 0;
+}
+
+/**
+ * @return
+ * - 0 on successful refill
+ * - a negative number when bitstream end is hit
+ *
+ * Always succeeds when UNCHECKED_BITSTREAM_READER is enabled.
+ */
+static inline int bits_priv_refill_32(BitstreamContext *bc)
+{
+#if !UNCHECKED_BITSTREAM_READER
+ if (bc->ptr >= bc->buffer_end)
+ return -1;
+#endif
+
+#ifdef BITSTREAM_READER_LE
+ bc->bits |= (uint64_t)AV_RL32(bc->ptr) << bc->bits_valid;
+#else
+ bc->bits |= (uint64_t)AV_RB32(bc->ptr) << (32 - bc->bits_valid);
+#endif
+ bc->ptr += 4;
+ bc->bits_valid += 32;
+
+ return 0;
+}
+
+/**
+ * Initialize BitstreamContext.
+ * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
+ * larger than the actual read bits because some optimized bitstream
+ * readers read 32 or 64 bits at once and could read over the end
+ * @param bit_size the size of the buffer in bits
+ * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
+ */
+static inline int bits_init(BitstreamContext *bc, const uint8_t *buffer,
+ unsigned int bit_size)
+{
+ unsigned int buffer_size;
+
+ if (bit_size > INT_MAX - 7 || !buffer) {
+ bc->buffer = NULL;
+ bc->ptr = NULL;
+ bc->bits_valid = 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_valid = 0;
+ bc->bits = 0;
+
+ bits_priv_refill_64(bc);
+
+ return 0;
+}
+
+/**
+ * Initialize BitstreamContext.
+ * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
+ * larger than the actual read bits because some optimized bitstream
+ * readers read 32 or 64 bits at once and could read over the end
+ * @param byte_size the size of the buffer in bytes
+ * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow
+ */
+static inline int bits_init8(BitstreamContext *bc, const uint8_t *buffer,
+ unsigned int byte_size)
+{
+ if (byte_size > INT_MAX / 8)
+ return AVERROR_INVALIDDATA;
+ return bits_init(bc, buffer, byte_size * 8);
+}
+
+/**
+ * Return number of bits already read.
+ */
+static inline int bits_tell(const BitstreamContext *bc)
+{
+ return (bc->ptr - bc->buffer) * 8 - bc->bits_valid;
+}
+
+/**
+ * Return buffer size in bits.
+ */
+static inline int bits_size(const BitstreamContext *bc)
+{
+ return bc->size_in_bits;
+}
+
+/**
+ * Return the number of the bits left in a buffer.
+ */
+static inline int bits_left(const BitstreamContext *bc)
+{
+ return (bc->buffer - bc->ptr) * 8 + bc->size_in_bits + bc->bits_valid;
+}
+
+static inline uint64_t bits_priv_val_show(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n > 0 && n <= 64);
+
+#ifdef BITSTREAM_READER_LE
+ return bc->bits & (UINT64_MAX >> (64 - n));
+#else
+ return bc->bits >> (64 - n);
+#endif
+}
+
+static inline void bits_priv_skip_remaining(BitstreamContext *bc, unsigned int n)
+{
+#ifdef BITSTREAM_READER_LE
+ bc->bits >>= n;
+#else
+ bc->bits <<= n;
+#endif
+ bc->bits_valid -= n;
+}
+
+static inline uint64_t bits_priv_val_get(BitstreamContext *bc, unsigned int n)
+{
+ uint64_t ret;
+
+ av_assert2(n > 0 && n < 64);
+
+ ret = bits_priv_val_show(bc, n);
+ bits_priv_skip_remaining(bc, n);
+
+ return ret;
+}
+
+/**
+ * Return one bit from the buffer.
+ */
+static inline unsigned int bits_read_bit(BitstreamContext *bc)
+{
+ if (!bc->bits_valid && bits_priv_refill_64(bc) < 0)
+ return 0;
+
+ return bits_priv_val_get(bc, 1);
+}
+
+/**
+ * Return n bits from the buffer, n has to be in the 1-32 range.
+ * May be faster than bits_read() when n is not a compile-time constant and is
+ * known to be non-zero;
+ */
+static inline uint32_t bits_read_nz(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n > 0 && n <= 32);
+
+ if (n > bc->bits_valid) {
+ if (bits_priv_refill_32(bc) < 0)
+ bc->bits_valid = n;
+ }
+
+ return bits_priv_val_get(bc, n);
+}
+
+/**
+ * Return n bits from the buffer, n has to be in the 0-32 range.
+ */
+static inline uint32_t bits_read(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n <= 32);
+
+ if (!n)
+ return 0;
+
+ return bits_read_nz(bc, n);
+}
+
+/**
+ * Return n bits from the buffer, n has to be in the 0-63 range.
+ */
+static inline uint64_t bits_read_63(BitstreamContext *bc, unsigned int n)
+{
+ uint64_t ret = 0;
+ unsigned left = 0;
+
+ av_assert2(n <= 63);
+
+ if (!n)
+ return 0;
+
+ if (n > bc->bits_valid) {
+ left = bc->bits_valid;
+ n -= left;
+
+ if (left)
+ ret = bits_priv_val_get(bc, left);
+
+ if (bits_priv_refill_64(bc) < 0)
+ bc->bits_valid = n;
+
+ }
+
+#ifdef BITSTREAM_READER_LE
+ ret = bits_priv_val_get(bc, n) << left | ret;
+#else
+ ret = bits_priv_val_get(bc, n) | ret << n;
+#endif
+
+ return ret;
+}
+
+/**
+ * Return n bits from the buffer, n has to be in the 0-64 range.
+ */
+static inline uint64_t bits_read_64(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n <= 64);
+
+ if (n == 64) {
+ uint64_t ret = bits_read_63(bc, 63);
+#ifdef BITSTREAM_READER_LE
+ return ret | ((uint64_t)bits_read_bit(bc) << 63);
+#else
+ return (ret << 1) | (uint64_t)bits_read_bit(bc);
+#endif
+ }
+ return bits_read_63(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 bits_read_signed(BitstreamContext *bc, unsigned int n)
+{
+ return sign_extend(bits_read(bc, n), n);
+}
+
+/**
+ * Return n bits from the buffer but do not change the buffer state.
+ * n has to be in the 1-32 range. May
+ */
+static inline uint32_t bits_peek_nz(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n > 0 && n <= 32);
+
+ if (n > bc->bits_valid)
+ bits_priv_refill_32(bc);
+
+ return bits_priv_val_show(bc, n);
+}
+
+/**
+ * Return n bits from the buffer but do not change the buffer state.
+ * n has to be in the 0-32 range.
+ */
+static inline uint32_t bits_peek(BitstreamContext *bc, unsigned int n)
+{
+ av_assert2(n <= 32);
+
+ if (!n)
+ return 0;
+
+ return bits_peek_nz(bc, n);
+}
+
+/**
+ * Return n bits from the buffer as a signed integer,
+ * do not change the buffer state.
+ * n has to be in the 0-32 range.
+ */
+static inline int bits_peek_signed(BitstreamContext *bc, unsigned int n)
+{
+ return sign_extend(bits_peek(bc, n), n);
+}
+
+/**
+ * Skip n bits in the buffer.
+ */
+static inline void bits_skip(BitstreamContext *bc, unsigned int n)
+{
+ if (n < bc->bits_valid)
+ bits_priv_skip_remaining(bc, n);
+ else {
+ n -= bc->bits_valid;
+ bc->bits = 0;
+ bc->bits_valid = 0;
+
+ if (n >= 64) {
+ unsigned int skip = n / 8;
+
+ n -= skip * 8;
+ bc->ptr += skip;
+ }
+ bits_priv_refill_64(bc);
+ if (n)
+ bits_priv_skip_remaining(bc, n);
+ }
+}
+
+/**
+ * Seek to the given bit position.
+ */
+static inline void bits_seek(BitstreamContext *bc, unsigned pos)
+{
+ bc->ptr = bc->buffer;
+ bc->bits = 0;
+ bc->bits_valid = 0;
+
+ bits_skip(bc, pos);
+}
+
+/**
+ * Skip bits to a byte boundary.
+ */
+static inline const uint8_t *bits_align(BitstreamContext *bc)
+{
+ unsigned int n = -bits_tell(bc) & 7;
+ if (n)
+ bits_skip(bc, n);
+ return bc->buffer + (bits_tell(bc) >> 3);
+}
+
+/**
+ * Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
+ * If MSB not set it is negative.
+ * @param n length in bits
+ */
+static inline int bits_read_xbits(BitstreamContext *bc, unsigned int n)
+{
+ int32_t cache = bits_peek(bc, 32);
+ int sign = ~cache >> 31;
+ bits_priv_skip_remaining(bc, n);
+
+ return ((((uint32_t)(sign ^ cache)) >> (32 - n)) ^ sign) - sign;
+}
+
+/**
+ * Return decoded truncated unary code for the values 0, 1, 2.
+ */
+static inline int bits_decode012(BitstreamContext *bc)
+{
+ if (!bits_read_bit(bc))
+ return 0;
+ else
+ return bits_read_bit(bc) + 1;
+}
+
+/**
+ * Return decoded truncated unary code for the values 2, 1, 0.
+ */
+static inline int bits_decode210(BitstreamContext *bc)
+{
+ if (bits_read_bit(bc))
+ return 0;
+ else
+ return 2 - bits_read_bit(bc);
+}
+
+/* Read sign bit and flip the sign of the provided value accordingly. */
+static inline int bits_apply_sign(BitstreamContext *bc, int val)
+{
+ int sign = bits_read_signed(bc, 1);
+ return (val ^ sign) - sign;
+}
+
+static inline int bits_skip_1stop_8data(BitstreamContext *s)
+{
+ if (bits_left(s) <= 0)
+ return AVERROR_INVALIDDATA;
+
+ while (bits_read_bit(s)) {
+ bits_skip(s, 8);
+ if (bits_left(s) <= 0)
+ return AVERROR_INVALIDDATA;
+ }
+
+ return 0;
+}
+
+/**
+ * Return the LUT element for the given bitstream configuration.
+ */
+static inline int bits_priv_set_idx(BitstreamContext *bc, int code, int *n, int *nb_bits,
+ const VLCElem *table)
+{
+ unsigned idx;
+
+ *nb_bits = -*n;
+ idx = bits_peek(bc, *nb_bits) + code;
+ *n = table[idx].len;
+
+ return table[idx].sym;
+}
+
+/**
+ * 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 bits_read_vlc(BitstreamContext *bc, const VLCElem *table,
+ int bits, int max_depth)
+{
+ int nb_bits;
+ unsigned idx = bits_peek(bc, bits);
+ int code = table[idx].sym;
+ int n = table[idx].len;
+
+ if (max_depth > 1 && n < 0) {
+ bits_priv_skip_remaining(bc, bits);
+ code = bits_priv_set_idx(bc, code, &n, &nb_bits, table);
+ if (max_depth > 2 && n < 0) {
+ bits_priv_skip_remaining(bc, nb_bits);
+ code = bits_priv_set_idx(bc, code, &n, &nb_bits, table);
+ }
+ }
+ bits_priv_skip_remaining(bc, n);
+
+ return code;
+}
+
+#define BITS_RL_VLC(level, run, bc, table, bits, max_depth) \
+ do { \
+ int n, nb_bits; \
+ unsigned int index = bits_peek(bc, bits); \
+ level = table[index].level; \
+ n = table[index].len; \
+ \
+ if (max_depth > 1 && n < 0) { \
+ bits_skip(bc, bits); \
+ \
+ nb_bits = -n; \
+ \
+ index = bits_peek(bc, nb_bits) + level; \
+ level = table[index].level; \
+ n = table[index].len; \
+ if (max_depth > 2 && n < 0) { \
+ bits_skip(bc, nb_bits); \
+ nb_bits = -n; \
+ \
+ index = bits_peek(bc, nb_bits) + level; \
+ level = table[index].level; \
+ n = table[index].len; \
+ } \
+ } \
+ run = table[index].run; \
+ bits_skip(bc, n); \
+ } while (0)
+
+#endif /* AVCODEC_BITSTREAM_H */