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
35 enum dirac_arith_contexts {
36 CTX_ZPZN_F1,
37 CTX_ZPNN_F1,
38 CTX_NPZN_F1,
39 CTX_NPNN_F1,
40 CTX_ZP_F2,
41 CTX_ZP_F3,
42 CTX_ZP_F4,
43 CTX_ZP_F5,
44 CTX_ZP_F6,
45 CTX_NP_F2,
46 CTX_NP_F3,
47 CTX_NP_F4,
48 CTX_NP_F5,
49 CTX_NP_F6,
50 CTX_COEFF_DATA,
51 CTX_SIGN_NEG,
52 CTX_SIGN_ZERO,
53 CTX_SIGN_POS,
54 CTX_ZERO_BLOCK,
55 CTX_DELTA_Q_F,
56 CTX_DELTA_Q_DATA,
57 CTX_DELTA_Q_SIGN,
58
59 DIRAC_CTX_COUNT
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
80 const uint8_t *bytestream;
81 const uint8_t *bytestream_end;
82
83 uint16_t contexts[DIRAC_CTX_COUNT];
84 int error;
85 int overread;
86 } DiracArith;
87
88 extern const uint8_t ff_dirac_next_ctx[DIRAC_CTX_COUNT];
89 extern const uint16_t ff_dirac_prob[256];
90 extern int16_t ff_dirac_prob_branchless[256][2];
91
renorm(DiracArith * c)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
refill(DiracArith * c)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)
125 c->error = AVERROR_INVALIDDATA;
126 }
127
128 c->low += new << counter;
129 counter -= 16;
130 }
131 c->counter = counter;
132 }
133
dirac_get_arith_bit(DiracArith * c,int ctx)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
dirac_get_arith_uint(DiracArith * c,int follow_ctx,int data_ctx)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");
181 c->error = AVERROR_INVALIDDATA;
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
dirac_get_arith_int(DiracArith * c,int follow_ctx,int data_ctx)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);
200 void ff_dirac_init_arith_decoder(DiracArith *c, GetBitContext *gb, int length);
201
202 #endif /* AVCODEC_DIRAC_ARITH_H */
203