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FFmpeg/libavcodec/golomb.h
Andreas Rheinhardt 2d5407d390 avcodec/golomb: Document return value of get_ue_golomb_31 on error 
get_ue_golomb_31() reads nine bits and an array with 512 entries to
parse golomb codes. The longest golomb codes that fit into 9 bits use
four leading zeroes and five value bits and can encode numbers in the
0..30 range. 31 meanwhile is encoded on 11 bits and if the nine bits
read coincide with the first nine bits of the encoding of 31,
get_ue_golomb_31() returns 31 (and skips 11 bits).

But looking at the first nine bits only makes it impossible to distinguish
31 from 32..34. Therefore the documentation of get_ue_golomb_31() simply
states that the return value is undefined if the value of the encountered
exp golomb code was outside the 0..31 range.

But actually get_ue_golomb_31() does not behave that bad: If the returned
value is in the range of 0..30, then this is the actually encountered value,
so that this function can be used without any problems to parse and validate
parameters whose legal values are a subset of the 0..30 range.

This commit documents this fact.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
2020-07-29 05:06:35 +02:00

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/*
* exp golomb vlc stuff
* Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
* Copyright (c) 2004 Alex Beregszaszi
*
* 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
* @brief
* exp golomb vlc stuff
* @author Michael Niedermayer <michaelni@gmx.at> and Alex Beregszaszi
*/
#ifndef AVCODEC_GOLOMB_H
#define AVCODEC_GOLOMB_H
#include <stdint.h>
#include "get_bits.h"
#include "put_bits.h"
#define INVALID_VLC 0x80000000
extern const uint8_t ff_golomb_vlc_len[512];
extern const uint8_t ff_ue_golomb_vlc_code[512];
extern const int8_t ff_se_golomb_vlc_code[512];
extern const uint8_t ff_ue_golomb_len[256];
extern const uint8_t ff_interleaved_golomb_vlc_len[256];
extern const uint8_t ff_interleaved_ue_golomb_vlc_code[256];
extern const int8_t ff_interleaved_se_golomb_vlc_code[256];
extern const uint8_t ff_interleaved_dirac_golomb_vlc_code[256];
/**
* Read an unsigned Exp-Golomb code in the range 0 to 8190.
*
* @returns the read value or a negative error code.
*/
static inline int get_ue_golomb(GetBitContext *gb)
{
unsigned int buf;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
if (buf >= (1 << 27)) {
buf >>= 32 - 9;
skip_bits_long(gb, ff_golomb_vlc_len[buf]);
return ff_ue_golomb_vlc_code[buf];
} else {
int log = 2 * av_log2(buf) - 31;
skip_bits_long(gb, 32 - log);
if (log < 7)
return AVERROR_INVALIDDATA;
buf >>= log;
buf--;
return buf;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
if (buf >= (1 << 27)) {
buf >>= 32 - 9;
LAST_SKIP_BITS(re, gb, ff_golomb_vlc_len[buf]);
CLOSE_READER(re, gb);
return ff_ue_golomb_vlc_code[buf];
} else {
int log = 2 * av_log2(buf) - 31;
LAST_SKIP_BITS(re, gb, 32 - log);
CLOSE_READER(re, gb);
if (log < 7)
return AVERROR_INVALIDDATA;
buf >>= log;
buf--;
return buf;
}
#endif
}
/**
* Read an unsigned Exp-Golomb code in the range 0 to UINT32_MAX-1.
*/
static inline unsigned get_ue_golomb_long(GetBitContext *gb)
{
unsigned buf, log;
buf = show_bits_long(gb, 32);
log = 31 - av_log2(buf);
skip_bits_long(gb, log);
return get_bits_long(gb, log + 1) - 1;
}
/**
* read unsigned exp golomb code, constraint to a max of 31.
* If the value encountered is not in 0..31, the return value
* is outside the range 0..30.
*/
static inline int get_ue_golomb_31(GetBitContext *gb)
{
unsigned int buf;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
buf >>= 32 - 9;
skip_bits_long(gb, ff_golomb_vlc_len[buf]);
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
buf >>= 32 - 9;
LAST_SKIP_BITS(re, gb, ff_golomb_vlc_len[buf]);
CLOSE_READER(re, gb);
#endif
return ff_ue_golomb_vlc_code[buf];
}
static inline unsigned get_interleaved_ue_golomb(GetBitContext *gb)
{
uint32_t buf;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
if (buf & 0xAA800000) {
buf >>= 32 - 8;
skip_bits_long(gb, ff_interleaved_golomb_vlc_len[buf]);
return ff_interleaved_ue_golomb_vlc_code[buf];
} else {
unsigned ret = 1;
do {
buf >>= 32 - 8;
skip_bits_long(gb, FFMIN(ff_interleaved_golomb_vlc_len[buf], 8));
if (ff_interleaved_golomb_vlc_len[buf] != 9) {
ret <<= (ff_interleaved_golomb_vlc_len[buf] - 1) >> 1;
ret |= ff_interleaved_dirac_golomb_vlc_code[buf];
break;
}
ret = (ret << 4) | ff_interleaved_dirac_golomb_vlc_code[buf];
buf = show_bits_long(gb, 32);
} while (get_bits_left(gb) > 0);
return ret - 1;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
if (buf & 0xAA800000) {
buf >>= 32 - 8;
LAST_SKIP_BITS(re, gb, ff_interleaved_golomb_vlc_len[buf]);
CLOSE_READER(re, gb);
return ff_interleaved_ue_golomb_vlc_code[buf];
} else {
unsigned ret = 1;
do {
buf >>= 32 - 8;
LAST_SKIP_BITS(re, gb,
FFMIN(ff_interleaved_golomb_vlc_len[buf], 8));
if (ff_interleaved_golomb_vlc_len[buf] != 9) {
ret <<= (ff_interleaved_golomb_vlc_len[buf] - 1) >> 1;
ret |= ff_interleaved_dirac_golomb_vlc_code[buf];
break;
}
ret = (ret << 4) | ff_interleaved_dirac_golomb_vlc_code[buf];
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
} while (ret<0x8000000U && BITS_AVAILABLE(re, gb));
CLOSE_READER(re, gb);
return ret - 1;
}
#endif
}
/**
* read unsigned truncated exp golomb code.
*/
static inline int get_te0_golomb(GetBitContext *gb, int range)
{
av_assert2(range >= 1);
if (range == 1)
return 0;
else if (range == 2)
return get_bits1(gb) ^ 1;
else
return get_ue_golomb(gb);
}
/**
* read unsigned truncated exp golomb code.
*/
static inline int get_te_golomb(GetBitContext *gb, int range)
{
av_assert2(range >= 1);
if (range == 2)
return get_bits1(gb) ^ 1;
else
return get_ue_golomb(gb);
}
/**
* read signed exp golomb code.
*/
static inline int get_se_golomb(GetBitContext *gb)
{
unsigned int buf;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
if (buf >= (1 << 27)) {
buf >>= 32 - 9;
skip_bits_long(gb, ff_golomb_vlc_len[buf]);
return ff_se_golomb_vlc_code[buf];
} else {
int log = 2 * av_log2(buf) - 31;
buf >>= log;
skip_bits_long(gb, 32 - log);
if (buf & 1)
buf = -(buf >> 1);
else
buf = (buf >> 1);
return buf;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
if (buf >= (1 << 27)) {
buf >>= 32 - 9;
LAST_SKIP_BITS(re, gb, ff_golomb_vlc_len[buf]);
CLOSE_READER(re, gb);
return ff_se_golomb_vlc_code[buf];
} else {
int log = av_log2(buf), sign;
LAST_SKIP_BITS(re, gb, 31 - log);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
buf >>= log;
LAST_SKIP_BITS(re, gb, 32 - log);
CLOSE_READER(re, gb);
sign = -(buf & 1);
buf = ((buf >> 1) ^ sign) - sign;
return buf;
}
#endif
}
static inline int get_se_golomb_long(GetBitContext *gb)
{
unsigned int buf = get_ue_golomb_long(gb);
int sign = (buf & 1) - 1;
return ((buf >> 1) ^ sign) + 1;
}
static inline int get_interleaved_se_golomb(GetBitContext *gb)
{
unsigned int buf;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
if (buf & 0xAA800000) {
buf >>= 32 - 8;
skip_bits_long(gb, ff_interleaved_golomb_vlc_len[buf]);
return ff_interleaved_se_golomb_vlc_code[buf];
} else {
int log;
skip_bits(gb, 8);
buf |= 1 | show_bits(gb, 24);
if ((buf & 0xAAAAAAAA) == 0)
return INVALID_VLC;
for (log = 31; (buf & 0x80000000) == 0; log--)
buf = (buf << 2) - ((buf << log) >> (log - 1)) + (buf >> 30);
skip_bits_long(gb, 63 - 2 * log - 8);
return (signed) (((((buf << log) >> log) - 1) ^ -(buf & 0x1)) + 1) >> 1;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
if (buf & 0xAA800000) {
buf >>= 32 - 8;
LAST_SKIP_BITS(re, gb, ff_interleaved_golomb_vlc_len[buf]);
CLOSE_READER(re, gb);
return ff_interleaved_se_golomb_vlc_code[buf];
} else {
int log;
LAST_SKIP_BITS(re, gb, 8);
UPDATE_CACHE(re, gb);
buf |= 1 | (GET_CACHE(re, gb) >> 8);
if ((buf & 0xAAAAAAAA) == 0)
return INVALID_VLC;
for (log = 31; (buf & 0x80000000) == 0; log--)
buf = (buf << 2) - ((buf << log) >> (log - 1)) + (buf >> 30);
LAST_SKIP_BITS(re, gb, 63 - 2 * log - 8);
CLOSE_READER(re, gb);
return (signed) (((((buf << log) >> log) - 1) ^ -(buf & 0x1)) + 1) >> 1;
}
#endif
}
static inline int dirac_get_se_golomb(GetBitContext *gb)
{
uint32_t ret = get_interleaved_ue_golomb(gb);
if (ret) {
int sign = -get_bits1(gb);
ret = (ret ^ sign) - sign;
}
return ret;
}
/**
* read unsigned golomb rice code (ffv1).
*/
static inline int get_ur_golomb(GetBitContext *gb, int k, int limit,
int esc_len)
{
unsigned int buf;
int log;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
log = av_log2(buf);
if (log > 31 - limit) {
buf >>= log - k;
buf += (30 - log) << k;
skip_bits_long(gb, 32 + k - log);
return buf;
} else {
skip_bits_long(gb, limit);
buf = get_bits_long(gb, esc_len);
return buf + limit - 1;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
log = av_log2(buf);
if (log > 31 - limit) {
buf >>= log - k;
buf += (30U - log) << k;
LAST_SKIP_BITS(re, gb, 32 + k - log);
CLOSE_READER(re, gb);
return buf;
} else {
LAST_SKIP_BITS(re, gb, limit);
UPDATE_CACHE(re, gb);
buf = SHOW_UBITS(re, gb, esc_len);
LAST_SKIP_BITS(re, gb, esc_len);
CLOSE_READER(re, gb);
return buf + limit - 1;
}
#endif
}
/**
* read unsigned golomb rice code (jpegls).
*/
static inline int get_ur_golomb_jpegls(GetBitContext *gb, int k, int limit,
int esc_len)
{
unsigned int buf;
int log;
#if CACHED_BITSTREAM_READER
buf = show_bits_long(gb, 32);
log = av_log2(buf);
if (log - k >= 1 && 32 - log < limit) {
buf >>= log - k;
buf += (30 - log) << k;
skip_bits_long(gb, 32 + k - log);
return buf;
} else {
int i;
for (i = 0;
i < limit && get_bits1(gb) == 0 && get_bits_left(gb) > 0;
i++);
if (i < limit - 1) {
buf = get_bits_long(gb, k);
return buf + (i << k);
} else if (i == limit - 1) {
buf = get_bits_long(gb, esc_len);
return buf + 1;
} else
return -1;
}
#else
OPEN_READER(re, gb);
UPDATE_CACHE(re, gb);
buf = GET_CACHE(re, gb);
log = av_log2(buf);
av_assert2(k <= 31);
if (log - k >= 32 - MIN_CACHE_BITS + (MIN_CACHE_BITS == 32) &&
32 - log < limit) {
buf >>= log - k;
buf += (30U - log) << k;
LAST_SKIP_BITS(re, gb, 32 + k - log);
CLOSE_READER(re, gb);
return buf;
} else {
int i;
for (i = 0; i + MIN_CACHE_BITS <= limit && SHOW_UBITS(re, gb, MIN_CACHE_BITS) == 0; i += MIN_CACHE_BITS) {
if (gb->size_in_bits <= re_index) {
CLOSE_READER(re, gb);
return -1;
}
LAST_SKIP_BITS(re, gb, MIN_CACHE_BITS);
UPDATE_CACHE(re, gb);
}
for (; i < limit && SHOW_UBITS(re, gb, 1) == 0; i++) {
SKIP_BITS(re, gb, 1);
}
LAST_SKIP_BITS(re, gb, 1);
UPDATE_CACHE(re, gb);
if (i < limit - 1) {
if (k) {
if (k > MIN_CACHE_BITS - 1) {
buf = SHOW_UBITS(re, gb, 16) << (k-16);
LAST_SKIP_BITS(re, gb, 16);
UPDATE_CACHE(re, gb);
buf |= SHOW_UBITS(re, gb, k-16);
LAST_SKIP_BITS(re, gb, k-16);
} else {
buf = SHOW_UBITS(re, gb, k);
LAST_SKIP_BITS(re, gb, k);
}
} else {
buf = 0;
}
buf += ((SUINT)i << k);
} else if (i == limit - 1) {
buf = SHOW_UBITS(re, gb, esc_len);
LAST_SKIP_BITS(re, gb, esc_len);
buf ++;
} else {
buf = -1;
}
CLOSE_READER(re, gb);
return buf;
}
#endif
}
/**
* read signed golomb rice code (ffv1).
*/
static inline int get_sr_golomb(GetBitContext *gb, int k, int limit,
int esc_len)
{
unsigned v = get_ur_golomb(gb, k, limit, esc_len);
return (v >> 1) ^ -(v & 1);
}
/**
* read signed golomb rice code (flac).
*/
static inline int get_sr_golomb_flac(GetBitContext *gb, int k, int limit,
int esc_len)
{
unsigned v = get_ur_golomb_jpegls(gb, k, limit, esc_len);
return (v >> 1) ^ -(v & 1);
}
/**
* read unsigned golomb rice code (shorten).
*/
static inline unsigned int get_ur_golomb_shorten(GetBitContext *gb, int k)
{
return get_ur_golomb_jpegls(gb, k, INT_MAX, 0);
}
/**
* read signed golomb rice code (shorten).
*/
static inline int get_sr_golomb_shorten(GetBitContext *gb, int k)
{
int uvar = get_ur_golomb_jpegls(gb, k + 1, INT_MAX, 0);
return (uvar >> 1) ^ -(uvar & 1);
}
#ifdef TRACE
static inline int get_ue(GetBitContext *s, const char *file, const char *func,
int line)
{
int show = show_bits(s, 24);
int pos = get_bits_count(s);
int i = get_ue_golomb(s);
int len = get_bits_count(s) - pos;
int bits = show >> (24 - len);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d ue @%5d in %s %s:%d\n",
bits, len, i, pos, file, func, line);
return i;
}
static inline int get_se(GetBitContext *s, const char *file, const char *func,
int line)
{
int show = show_bits(s, 24);
int pos = get_bits_count(s);
int i = get_se_golomb(s);
int len = get_bits_count(s) - pos;
int bits = show >> (24 - len);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d se @%5d in %s %s:%d\n",
bits, len, i, pos, file, func, line);
return i;
}
static inline int get_te(GetBitContext *s, int r, char *file, const char *func,
int line)
{
int show = show_bits(s, 24);
int pos = get_bits_count(s);
int i = get_te0_golomb(s, r);
int len = get_bits_count(s) - pos;
int bits = show >> (24 - len);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d te @%5d in %s %s:%d\n",
bits, len, i, pos, file, func, line);
return i;
}
#define get_ue_golomb(a) get_ue(a, __FILE__, __func__, __LINE__)
#define get_se_golomb(a) get_se(a, __FILE__, __func__, __LINE__)
#define get_te_golomb(a, r) get_te(a, r, __FILE__, __func__, __LINE__)
#define get_te0_golomb(a, r) get_te(a, r, __FILE__, __func__, __LINE__)
#endif /* TRACE */
/**
* write unsigned exp golomb code. 2^16 - 2 at most
*/
static inline void set_ue_golomb(PutBitContext *pb, int i)
{
av_assert2(i >= 0);
av_assert2(i <= 0xFFFE);
if (i < 256)
put_bits(pb, ff_ue_golomb_len[i], i + 1);
else {
int e = av_log2(i + 1);
put_bits(pb, 2 * e + 1, i + 1);
}
}
/**
* write unsigned exp golomb code. 2^32-2 at most.
*/
static inline void set_ue_golomb_long(PutBitContext *pb, uint32_t i)
{
av_assert2(i <= (UINT32_MAX - 1));
if (i < 256)
put_bits(pb, ff_ue_golomb_len[i], i + 1);
else {
int e = av_log2(i + 1);
put_bits64(pb, 2 * e + 1, i + 1);
}
}
/**
* write truncated unsigned exp golomb code.
*/
static inline void set_te_golomb(PutBitContext *pb, int i, int range)
{
av_assert2(range >= 1);
av_assert2(i <= range);
if (range == 2)
put_bits(pb, 1, i ^ 1);
else
set_ue_golomb(pb, i);
}
/**
* write signed exp golomb code. 16 bits at most.
*/
static inline void set_se_golomb(PutBitContext *pb, int i)
{
i = 2 * i - 1;
if (i < 0)
i ^= -1; //FIXME check if gcc does the right thing
set_ue_golomb(pb, i);
}
/**
* write unsigned golomb rice code (ffv1).
*/
static inline void set_ur_golomb(PutBitContext *pb, int i, int k, int limit,
int esc_len)
{
int e;
av_assert2(i >= 0);
e = i >> k;
if (e < limit)
put_bits(pb, e + k + 1, (1 << k) + av_mod_uintp2(i, k));
else
put_bits(pb, limit + esc_len, i - limit + 1);
}
/**
* write unsigned golomb rice code (jpegls).
*/
static inline void set_ur_golomb_jpegls(PutBitContext *pb, int i, int k,
int limit, int esc_len)
{
int e;
av_assert2(i >= 0);
e = (i >> k) + 1;
if (e < limit) {
while (e > 31) {
put_bits(pb, 31, 0);
e -= 31;
}
put_bits(pb, e, 1);
if (k)
put_sbits(pb, k, i);
} else {
while (limit > 31) {
put_bits(pb, 31, 0);
limit -= 31;
}
put_bits(pb, limit, 1);
put_bits(pb, esc_len, i - 1);
}
}
/**
* write signed golomb rice code (ffv1).
*/
static inline void set_sr_golomb(PutBitContext *pb, int i, int k, int limit,
int esc_len)
{
int v;
v = -2 * i - 1;
v ^= (v >> 31);
set_ur_golomb(pb, v, k, limit, esc_len);
}
/**
* write signed golomb rice code (flac).
*/
static inline void set_sr_golomb_flac(PutBitContext *pb, int i, int k,
int limit, int esc_len)
{
int v;
v = -2 * i - 1;
v ^= (v >> 31);
set_ur_golomb_jpegls(pb, v, k, limit, esc_len);
}
#endif /* AVCODEC_GOLOMB_H */
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