crc.h
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1 /*
2  * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * FFmpeg is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with FFmpeg; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #ifndef AVUTIL_CRC_H
22 #define AVUTIL_CRC_H
23 
24 #include <stdint.h>
25 #include <stddef.h>
26 #include "attributes.h"
27 
28 typedef uint32_t AVCRC;
29 
30 typedef enum {
35  AV_CRC_32_IEEE_LE, /*< reversed bitorder version of AV_CRC_32_IEEE */
36  AV_CRC_MAX, /*< Not part of public API! Do not use outside libavutil. */
37 }AVCRCId;
38 
39 /**
40  * Initialize a CRC table.
41  * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
42  * @param le If 1, the lowest bit represents the coefficient for the highest
43  * exponent of the corresponding polynomial (both for poly and
44  * actual CRC).
45  * If 0, you must swap the CRC parameter and the result of av_crc
46  * if you need the standard representation (can be simplified in
47  * most cases to e.g. bswap16):
48  * av_bswap32(crc << (32-bits))
49  * @param bits number of bits for the CRC
50  * @param poly generator polynomial without the x**bits coefficient, in the
51  * representation as specified by le
52  * @param ctx_size size of ctx in bytes
53  * @return <0 on failure
54  */
55 int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size);
56 
57 /**
58  * Get an initialized standard CRC table.
59  * @param crc_id ID of a standard CRC
60  * @return a pointer to the CRC table or NULL on failure
61  */
62 const AVCRC *av_crc_get_table(AVCRCId crc_id);
63 
64 /**
65  * Calculate the CRC of a block.
66  * @param crc CRC of previous blocks if any or initial value for CRC
67  * @return CRC updated with the data from the given block
68  *
69  * @see av_crc_init() "le" parameter
70  */
71 uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
72  const uint8_t *buffer, size_t length) av_pure;
73 
74 #endif /* AVUTIL_CRC_H */
Definition: crc.h:36
uint32_t poly
Definition: crc.c:217
const AVCRC * av_crc_get_table(AVCRCId crc_id)
Get an initialized standard CRC table.
Definition: crc.c:261
#define av_pure
Definition: attributes.h:62
uint32_t av_crc(const AVCRC *ctx, uint32_t crc, const uint8_t *buffer, size_t length) av_pure
Calculate the CRC of a block.
Definition: crc.c:275
Macro definitions for various function/variable attributes.
uint8_t bits
Definition: crc.c:216
uint8_t
AVCRCId
Definition: crc.h:30
uint8_t le
Definition: crc.c:215
int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
Initialize a CRC table.
Definition: crc.c:228
the buffer and buffer reference mechanism is intended to as much as expensive copies of that data while still allowing the filters to produce correct results The data is stored in buffers represented by AVFilterBuffer structures They must not be accessed but through references stored in AVFilterBufferRef structures Several references can point to the same buffer
uint32_t AVCRC
Definition: crc.h:28
const char int length
Definition: avisynth_c.h:668