crc.h File Reference

#include <stdint.h>
#include <stddef.h>
#include "common.h"

Go to the source code of this file.

Typedefs
typedef uint32_t	AVCRC
Enumerations
enum	AVCRCId {   AV_CRC_8_ATM, AV_CRC_16_ANSI, AV_CRC_16_CCITT, AV_CRC_32_IEEE,   AV_CRC_32_IEEE_LE, AV_CRC_MAX }
Functions
int	av_crc_init (AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
const AVCRC *	av_crc_get_table (AVCRCId crc_id)
uint32_t	av_crc (const AVCRC *ctx, uint32_t start_crc, const uint8_t *buffer, size_t length) av_pure

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Typedef Documentation

typedef uint32_t AVCRC

Definition at line 28 of file crc.h.

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Enumeration Type Documentation

enum AVCRCId

Enumerator:

AV_CRC_8_ATM
AV_CRC_16_ANSI
AV_CRC_16_CCITT
AV_CRC_32_IEEE
AV_CRC_32_IEEE_LE
AV_CRC_MAX

Definition at line 30 of file crc.h.

             {
    AV_CRC_8_ATM,
    AV_CRC_16_ANSI,
    AV_CRC_16_CCITT,
    AV_CRC_32_IEEE,
    AV_CRC_32_IEEE_LE,  /*< reversed bitorder version of AV_CRC_32_IEEE */
    AV_CRC_MAX,         /*< not part of public API! don't use outside lavu */
}AVCRCId;

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Function Documentation

uint32_t av_crc	(	const AVCRC *	ctx,
		uint32_t	crc,
		const uint8_t *	buffer,
		size_t	length
	)

Calculate the CRC of a block

Parameters:

crc

CRC of previous blocks if any or initial value for CRC.

Returns:

CRC updated with the data from the given block

See also:

av_crc_init() "le" parameter

Definition at line 112 of file crc.c.

References le2me_32.

Referenced by ac3_decode_frame(), ac3_probe(), decode_frame(), ff_crc04C11DB7_update(), mlp_checksum16(), mlp_checksum8(), mlp_restart_checksum(), mpegts_write_section(), output_frame_end(), output_frame_footer(), output_frame_header(), and write_section_data().

                                                                                     {
    const uint8_t *end= buffer+length;

#ifndef CONFIG_SMALL
    if(!ctx[256])
        while(buffer<end-3){
            crc ^= le2me_32(*(const uint32_t*)buffer); buffer+=4;
            crc =  ctx[3*256 + ( crc     &0xFF)]
                  ^ctx[2*256 + ((crc>>8 )&0xFF)]
                  ^ctx[1*256 + ((crc>>16)&0xFF)]
                  ^ctx[0*256 + ((crc>>24)     )];
        }
#endif
    while(buffer<end)
        crc = ctx[((uint8_t)crc) ^ *buffer++] ^ (crc >> 8);

    return crc;
}

const AVCRC* av_crc_get_table

(

AVCRCId

crc_id

)

Get an initialized standard CRC table.

Parameters:

crc_id

ID of a standard CRC

Returns:

a pointer to the CRC table or NULL on failure

Definition at line 92 of file crc.c.

References av_crc_init(), av_crc_table, av_crc_table_params, bits, le, NULL, and poly.

Referenced by ac3_decode_frame(), ac3_probe(), decode_frame(), ff_crc04C11DB7_update(), mpegts_write_section(), output_frame_end(), output_frame_footer(), output_frame_header(), and write_section_data().

                                             {
#ifndef CONFIG_HARDCODED_TABLES
    if (!av_crc_table[crc_id][sizeof(av_crc_table[crc_id])/sizeof(av_crc_table[crc_id][0])-1])
        if (av_crc_init(av_crc_table[crc_id],
                        av_crc_table_params[crc_id].le,
                        av_crc_table_params[crc_id].bits,
                        av_crc_table_params[crc_id].poly,
                        sizeof(av_crc_table[crc_id])) < 0)
            return NULL;
#endif
    return av_crc_table[crc_id];
}

int av_crc_init	(	AVCRC *	ctx,
		int	le,
		int	bits,
		uint32_t	poly,
		int	ctx_size
	)

Inits a crc table.

Parameters:

	ctx	must be an array of sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
	cts_size	size of ctx in bytes
	le	if 1, lowest bit represents coefficient for highest exponent of corresponding polynomial (both for poly and actual CRC). If 0, you must swap the crc parameter and the result of av_crc if you need the standard representation (can be simplified in most cases to e.g. bswap16): bswap_32(crc << (32-bits))
	bits	number of bits for the CRC
	poly	generator polynomial without the x**bits coefficient, in the representation as specified by le

Returns:

<0 on failure

Definition at line 56 of file crc.c.

References bswap_32(), and c.

Referenced by av_crc_get_table(), init_static(), and mlp_checksum16().

                                                                          {
    int i, j;
    uint32_t c;

    if (bits < 8 || bits > 32 || poly >= (1LL<<bits))
        return -1;
    if (ctx_size != sizeof(AVCRC)*257 && ctx_size != sizeof(AVCRC)*1024)
        return -1;

    for (i = 0; i < 256; i++) {
        if (le) {
            for (c = i, j = 0; j < 8; j++)
                c = (c>>1)^(poly & (-(c&1)));
            ctx[i] = c;
        } else {
            for (c = i << 24, j = 0; j < 8; j++)
                c = (c<<1) ^ ((poly<<(32-bits)) & (((int32_t)c)>>31) );
            ctx[i] = bswap_32(c);
        }
    }
    ctx[256]=1;
#ifndef CONFIG_SMALL
    if(ctx_size >= sizeof(AVCRC)*1024)
        for (i = 0; i < 256; i++)
            for(j=0; j<3; j++)
                ctx[256*(j+1) + i]= (ctx[256*j + i]>>8) ^ ctx[ ctx[256*j + i]&0xFF ];
#endif

    return 0;
}

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