The Tor Browser / file comparison
comparison: media/libvpx/vp9/decoder/vp9_dboolhuff.c
media/libvpx/vp9/decoder/vp9_dboolhuff.c
- branch
- TOR_BUG_9701
- changeset 10
- ac0c01689b40
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| -1:000000000000 | 0:b68870ba8835 |
|---|---|
| 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 | |
| 11 #include "vpx_ports/mem.h" | |
| 12 #include "vpx_mem/vpx_mem.h" | |
| 13 | |
| 14 #include "vp9/decoder/vp9_dboolhuff.h" | |
| 15 | |
| 16 // This is meant to be a large, positive constant that can still be efficiently | |
| 17 // loaded as an immediate (on platforms like ARM, for example). | |
| 18 // Even relatively modest values like 100 would work fine. | |
| 19 #define LOTS_OF_BITS 0x40000000 | |
| 20 | |
| 21 | |
| 22 int vp9_reader_init(vp9_reader *r, const uint8_t *buffer, size_t size) { | |
| 23 int marker_bit; | |
| 24 | |
| 25 r->buffer_end = buffer + size; | |
| 26 r->buffer = buffer; | |
| 27 r->value = 0; | |
| 28 r->count = -8; | |
| 29 r->range = 255; | |
| 30 | |
| 31 if (size && !buffer) | |
| 32 return 1; | |
| 33 | |
| 34 vp9_reader_fill(r); | |
| 35 marker_bit = vp9_read_bit(r); | |
| 36 return marker_bit != 0; | |
| 37 } | |
| 38 | |
| 39 void vp9_reader_fill(vp9_reader *r) { | |
| 40 const uint8_t *const buffer_end = r->buffer_end; | |
| 41 const uint8_t *buffer = r->buffer; | |
| 42 VP9_BD_VALUE value = r->value; | |
| 43 int count = r->count; | |
| 44 int shift = BD_VALUE_SIZE - 8 - (count + 8); | |
| 45 int loop_end = 0; | |
| 46 const int bits_left = (int)((buffer_end - buffer)*CHAR_BIT); | |
| 47 const int x = shift + CHAR_BIT - bits_left; | |
| 48 | |
| 49 if (x >= 0) { | |
| 50 count += LOTS_OF_BITS; | |
| 51 loop_end = x; | |
| 52 } | |
| 53 | |
| 54 if (x < 0 || bits_left) { | |
| 55 while (shift >= loop_end) { | |
| 56 count += CHAR_BIT; | |
| 57 value |= (VP9_BD_VALUE)*buffer++ << shift; | |
| 58 shift -= CHAR_BIT; | |
| 59 } | |
| 60 } | |
| 61 | |
| 62 r->buffer = buffer; | |
| 63 r->value = value; | |
| 64 r->count = count; | |
| 65 } | |
| 66 | |
| 67 const uint8_t *vp9_reader_find_end(vp9_reader *r) { | |
| 68 // Find the end of the coded buffer | |
| 69 while (r->count > CHAR_BIT && r->count < BD_VALUE_SIZE) { | |
| 70 r->count -= CHAR_BIT; | |
| 71 r->buffer--; | |
| 72 } | |
| 73 return r->buffer; | |
| 74 } | |
| 75 | |
| 76 int vp9_reader_has_error(vp9_reader *r) { | |
| 77 // Check if we have reached the end of the buffer. | |
| 78 // | |
| 79 // Variable 'count' stores the number of bits in the 'value' buffer, minus | |
| 80 // 8. The top byte is part of the algorithm, and the remainder is buffered | |
| 81 // to be shifted into it. So if count == 8, the top 16 bits of 'value' are | |
| 82 // occupied, 8 for the algorithm and 8 in the buffer. | |
| 83 // | |
| 84 // When reading a byte from the user's buffer, count is filled with 8 and | |
| 85 // one byte is filled into the value buffer. When we reach the end of the | |
| 86 // data, count is additionally filled with LOTS_OF_BITS. So when | |
| 87 // count == LOTS_OF_BITS - 1, the user's data has been exhausted. | |
| 88 // | |
| 89 // 1 if we have tried to decode bits after the end of stream was encountered. | |
| 90 // 0 No error. | |
| 91 return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS; | |
| 92 } |
