1 /*
2 * Copyright (c) 2010 The WebM project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10 #include <stdlib.h>
11
12 #include "./vpx_config.h"
13
14 #include "vpx_dsp/bitreader.h"
15 #include "vpx_dsp/prob.h"
16 #include "vpx_dsp/vpx_dsp_common.h"
17 #include "vpx_ports/mem.h"
18 #include "vpx_mem/vpx_mem.h"
19 #include "vpx_util/endian_inl.h"
20
vpx_reader_init(vpx_reader * r,const uint8_t * buffer,size_t size,vpx_decrypt_cb decrypt_cb,void * decrypt_state)21 int vpx_reader_init(vpx_reader *r,
22 const uint8_t *buffer,
23 size_t size,
24 vpx_decrypt_cb decrypt_cb,
25 void *decrypt_state) {
26 if (size && !buffer) {
27 return 1;
28 } else {
29 r->buffer_end = buffer + size;
30 r->buffer = buffer;
31 r->value = 0;
32 r->count = -8;
33 r->range = 255;
34 r->decrypt_cb = decrypt_cb;
35 r->decrypt_state = decrypt_state;
36 vpx_reader_fill(r);
37 return vpx_read_bit(r) != 0; // marker bit
38 }
39 }
40
vpx_reader_fill(vpx_reader * r)41 void vpx_reader_fill(vpx_reader *r) {
42 const uint8_t *const buffer_end = r->buffer_end;
43 const uint8_t *buffer = r->buffer;
44 const uint8_t *buffer_start = buffer;
45 BD_VALUE value = r->value;
46 int count = r->count;
47 const size_t bytes_left = buffer_end - buffer;
48 const size_t bits_left = bytes_left * CHAR_BIT;
49 int shift = BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT);
50
51 if (r->decrypt_cb) {
52 size_t n = VPXMIN(sizeof(r->clear_buffer), bytes_left);
53 r->decrypt_cb(r->decrypt_state, buffer, r->clear_buffer, (int)n);
54 buffer = r->clear_buffer;
55 buffer_start = r->clear_buffer;
56 }
57 if (bits_left > BD_VALUE_SIZE) {
58 const int bits = (shift & 0xfffffff8) + CHAR_BIT;
59 BD_VALUE nv;
60 BD_VALUE big_endian_values;
61 memcpy(&big_endian_values, buffer, sizeof(BD_VALUE));
62 #if SIZE_MAX == 0xffffffffffffffffULL
63 big_endian_values = HToBE64(big_endian_values);
64 #else
65 big_endian_values = HToBE32(big_endian_values);
66 #endif
67 nv = big_endian_values >> (BD_VALUE_SIZE - bits);
68 count += bits;
69 buffer += (bits >> 3);
70 value = r->value | (nv << (shift & 0x7));
71 } else {
72 const int bits_over = (int)(shift + CHAR_BIT - bits_left);
73 int loop_end = 0;
74 if (bits_over >= 0) {
75 count += LOTS_OF_BITS;
76 loop_end = bits_over;
77 }
78
79 if (bits_over < 0 || bits_left) {
80 while (shift >= loop_end) {
81 count += CHAR_BIT;
82 value |= (BD_VALUE)*buffer++ << shift;
83 shift -= CHAR_BIT;
84 }
85 }
86 }
87
88 // NOTE: Variable 'buffer' may not relate to 'r->buffer' after decryption,
89 // so we increase 'r->buffer' by the amount that 'buffer' moved, rather than
90 // assign 'buffer' to 'r->buffer'.
91 r->buffer += buffer - buffer_start;
92 r->value = value;
93 r->count = count;
94 }
95
vpx_reader_find_end(vpx_reader * r)96 const uint8_t *vpx_reader_find_end(vpx_reader *r) {
97 // Find the end of the coded buffer
98 while (r->count > CHAR_BIT && r->count < BD_VALUE_SIZE) {
99 r->count -= CHAR_BIT;
100 r->buffer--;
101 }
102 return r->buffer;
103 }
104