FFmpeg  4.2.1
dirac_arith.h
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1 /*
2  * Copyright (C) 2007 Marco Gerards <marco@gnu.org>
3  * Copyright (C) 2009 David Conrad
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 /**
23  * @file
24  * Arithmetic decoder for Dirac
25  * @author Marco Gerards <marco@gnu.org>
26  */
27 
28 #ifndef AVCODEC_DIRAC_ARITH_H
29 #define AVCODEC_DIRAC_ARITH_H
30 
31 #include "libavutil/x86/asm.h"
32 #include "bytestream.h"
33 #include "get_bits.h"
34 
58 
60 };
61 
62 // Dirac resets the arith decoder between decoding various types of data,
63 // so many contexts are never used simultaneously. Thus, we can reduce
64 // the number of contexts needed by reusing them.
65 #define CTX_SB_F1 CTX_ZP_F5
66 #define CTX_SB_DATA 0
67 #define CTX_PMODE_REF1 0
68 #define CTX_PMODE_REF2 1
69 #define CTX_GLOBAL_BLOCK 2
70 #define CTX_MV_F1 CTX_ZP_F2
71 #define CTX_MV_DATA 0
72 #define CTX_DC_F1 CTX_ZP_F5
73 #define CTX_DC_DATA 0
74 
75 typedef struct {
76  unsigned low;
77  uint16_t range;
78  int16_t counter;
79 
82 
83  uint16_t contexts[DIRAC_CTX_COUNT];
84  int error;
85  int overread;
86 } DiracArith;
87 
89 extern const uint16_t ff_dirac_prob[256];
90 extern int16_t ff_dirac_prob_branchless[256][2];
91 
92 static inline void renorm(DiracArith *c)
93 {
94 #if HAVE_FAST_CLZ
95  int shift = 14 - av_log2_16bit(c->range-1) + ((c->range-1)>>15);
96 
97  c->low <<= shift;
98  c->range <<= shift;
99  c->counter += shift;
100 #else
101  while (c->range <= 0x4000) {
102  c->low <<= 1;
103  c->range <<= 1;
104  c->counter++;
105  }
106 #endif
107 }
108 
109 static inline void refill(DiracArith *c)
110 {
111  int counter = c->counter;
112 
113  if (counter >= 0) {
114  int new = bytestream_get_be16(&c->bytestream);
115 
116  // the spec defines overread bits to be 1, and streams rely on this
117  if (c->bytestream > c->bytestream_end) {
118  new |= 0xff;
119  if (c->bytestream > c->bytestream_end+1)
120  new |= 0xff00;
121 
122  c->bytestream = c->bytestream_end;
123  c->overread ++;
124  if (c->overread > 4)
126  }
127 
128  c->low += new << counter;
129  counter -= 16;
130  }
131  c->counter = counter;
132 }
133 
134 static inline int dirac_get_arith_bit(DiracArith *c, int ctx)
135 {
136  int prob_zero = c->contexts[ctx];
137  int range_times_prob, bit;
138  unsigned low = c->low;
139  int range = c->range;
140 
141  range_times_prob = (c->range * prob_zero) >> 16;
142 
143 #if ARCH_X86 && HAVE_FAST_CMOV && HAVE_INLINE_ASM && HAVE_6REGS
144  low -= range_times_prob << 16;
145  range -= range_times_prob;
146  bit = 0;
147  __asm__(
148  "cmpl %5, %4 \n\t"
149  "setae %b0 \n\t"
150  "cmovb %3, %2 \n\t"
151  "cmovb %5, %1 \n\t"
152  : "+q"(bit), "+r"(range), "+r"(low)
153  : "r"(c->low), "r"(c->low>>16),
154  "r"(range_times_prob)
155  );
156 #else
157  bit = (low >> 16) >= range_times_prob;
158  if (bit) {
159  low -= range_times_prob << 16;
160  range -= range_times_prob;
161  } else {
162  range = range_times_prob;
163  }
164 #endif
165 
166  c->contexts[ctx] += ff_dirac_prob_branchless[prob_zero>>8][bit];
167  c->low = low;
168  c->range = range;
169 
170  renorm(c);
171  refill(c);
172  return bit;
173 }
174 
175 static inline int dirac_get_arith_uint(DiracArith *c, int follow_ctx, int data_ctx)
176 {
177  int ret = 1;
178  while (!dirac_get_arith_bit(c, follow_ctx)) {
179  if (ret >= 0x40000000) {
180  av_log(NULL, AV_LOG_ERROR, "dirac_get_arith_uint overflow\n");
182  return -1;
183  }
184  ret <<= 1;
185  ret += dirac_get_arith_bit(c, data_ctx);
186  follow_ctx = ff_dirac_next_ctx[follow_ctx];
187  }
188  return ret-1;
189 }
190 
191 static inline int dirac_get_arith_int(DiracArith *c, int follow_ctx, int data_ctx)
192 {
193  int ret = dirac_get_arith_uint(c, follow_ctx, data_ctx);
194  if (ret && dirac_get_arith_bit(c, data_ctx+1))
195  ret = -ret;
196  return ret;
197 }
198 
199 void ff_dirac_init_arith_tables(void);
201 
202 #endif /* AVCODEC_DIRAC_ARITH_H */
#define NULL
Definition: coverity.c:32
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
static int shift(int a, int b)
Definition: sonic.c:82
int16_t ff_dirac_prob_branchless[256][2]
Definition: dirac_arith.c:84
uint16_t contexts[DIRAC_CTX_COUNT]
Definition: dirac_arith.h:83
static int dirac_get_arith_uint(DiracArith *c, int follow_ctx, int data_ctx)
Definition: dirac_arith.h:175
int16_t counter
Definition: dirac_arith.h:78
const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT]
Definition: dirac_arith.c:66
uint8_t
static void renorm(DiracArith *c)
Definition: dirac_arith.h:92
bitstream reader API header.
static void refill(DiracArith *c)
Definition: dirac_arith.h:109
uint16_t range
Definition: dirac_arith.h:77
#define av_log(a,...)
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:176
AVFormatContext * ctx
Definition: movenc.c:48
const uint8_t * bytestream
Definition: dirac_arith.h:80
const uint8_t * bytestream_end
Definition: dirac_arith.h:81
int overread
Definition: dirac_arith.h:85
static int dirac_get_arith_bit(DiracArith *c, int ctx)
Definition: dirac_arith.h:134
const uint16_t ff_dirac_prob[256]
Definition: dirac_arith.c:31
#define av_log2_16bit
Definition: intmath.h:84
unsigned low
Definition: dirac_arith.h:76
static double c[64]
static int dirac_get_arith_int(DiracArith *c, int follow_ctx, int data_ctx)
Definition: dirac_arith.h:191
void ff_dirac_init_arith_tables(void)
Definition: dirac_arith.c:86
const char int length
Definition: avisynth_c.h:860
dirac_arith_contexts
Definition: dirac_arith.h:35
void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length)
Definition: dirac_arith.c:96