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Clean VP8 header parser

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The old implementation has undefined behavior in it (unaligned read of uint32_t)
Now it's closer to the reference implementation:
https://tools.ietf.org/html/rfc6386#section-20.2

Also, added some comments and named some variables to make it more clear, that the
parser actually does.

Bug: chromium:1057551
Change-Id: I84c1912867e2794502e8a63302c938a0cbab2c4e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169545
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30661}
This commit is contained in:
Ilya Nikolaevskiy
2020-03-02 15:04:55 +01:00
committed by Commit Bot
parent 7d3f602dbc
commit ae92244054
2 changed files with 103 additions and 137 deletions
Download Patch File Download Diff File Expand all files Collapse all files

34
modules/video_coding/utility/vp8_header_parser.h
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@ -18,45 +18,17 @@ namespace webrtc {
namespace vp8 {
enum {
MB_FEATURE_TREE_PROBS = 3,
NUM_MB_SEGMENTS = 4,
NUM_REF_LF_DELTAS = 4,
NUM_MODE_LF_DELTAS = 4,
};
typedef struct VP8BitReader VP8BitReader;
struct VP8BitReader {
// Boolean decoder.
uint32_t value_; // Current value.
uint32_t range_; // Current range minus 1. In [127, 254] interval.
int bits_; // Number of valid bits left.
uint32_t value_; // Current value (2 bytes).
uint32_t range_; // Current range (always in [128..255] interval).
int bits_; // Number of bits shifted out of value, at most 7.
// Read buffer.
const uint8_t* buf_; // Next byte to be read.
const uint8_t* buf_end_; // End of read buffer.
int eof_; // True if input is exhausted.
};
const uint8_t kVP8Log2Range[128] = {
7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0};
// range = ((range - 1) << kVP8Log2Range[range]) + 1
const uint8_t kVP8NewRange[128] = {
127, 127, 191, 127, 159, 191, 223, 127, 143, 159, 175, 191, 207, 223, 239,
127, 135, 143, 151, 159, 167, 175, 183, 191, 199, 207, 215, 223, 231, 239,
247, 127, 131, 135, 139, 143, 147, 151, 155, 159, 163, 167, 171, 175, 179,
183, 187, 191, 195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239,
243, 247, 251, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149,
151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179,
181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201, 203, 205, 207, 209,
211, 213, 215, 217, 219, 221, 223, 225, 227, 229, 231, 233, 235, 237, 239,
241, 243, 245, 247, 249, 251, 253, 127};
// Gets the QP, QP range: [0, 127].
// Returns true on success, false otherwise.
bool GetQp(const uint8_t* buf, size_t length, int* qp);