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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 */