crcgen.c

TI的DSP C55X的应用程序

/***********************************************************************************/
/*                      IS54 Baseband Simulation Software                          */
/*                                                                                 */
/*  File Description : IS54 VSELP CRC Generator                                    */
/*  File Name        : crcgen.c                                                    */
/*  Date             : 12/30/93                                                    */
/*                   : July, 20001 - Modified for TMS320C55x project               */
/*                                                                                 */
/*    This file contains the function crcgen(), which takes a pointer              */
/*    to an array of IS54 VSELP parameters, extracts the CRC bits from             */
/*    the VSELP parameters, and then applies a generator polynomial to             */
/*    generate an output CRC which is re-stored back into the CRC field            */
/*    of the VSELP parameter array.                                                */
/*                                                                                 */
/*    Inputs:                                                                      */
/*            vselp      : Pointer to array of VSELP parameters                    */
/*                                                                                 */
/*    Outputs:                                                                     */
/*            vselp[CRC] : The CRC field of the VSELP parameter array              */
/*                         is updated with a re-generated CRC value.               */
/*                                                                                 */
/*    Return Value:                                                                */
/*              NONE                                                               */
/*                                                                                 */
/***********************************************************************************/

/* Include Files */

#include    "vselp.h"

/* Defines */ 

#define BIT0    0x0001
#define BIT1    0x0002
#define BIT2    0x0004
#define BIT3    0x0008
#define BIT4    0x0010
#define BIT5    0x0020
#define BIT6    0x0040
#define BIT7    0x0080 
#define BIT8    0x0100
#define BIT9    0x0200
#define BIT10   0x0400
#define BIT11   0x0800

#define TEST_BIT(num,mask)   (num & mask)   

/* Function Prototypes */

void    crcgen( unsigned * );

/* External Function Prototypes */

/* Data */

/* External Data */  

/* Code */

void    crcgen( unsigned *vselp )
{
    long unsigned   crcseed; /* generator polynomial */
    long unsigned   crcin;   /* CRC embedded in VSELP data */
    long unsigned   remain;  /* crc remainder */
    long unsigned   mask;    /* mask to AND with crcin to
                                determine whether MSB is 1 or 0  */
    int     i;               /* index value */   
    

   /* Extract CRC bits from VSELP parameters */
   
    crcin = 0;        
    if( TEST_BIT( vselp[ VSELP_LPC5 ], BIT3 ) ) crcin |= BIT0;
    if( TEST_BIT( vselp[ VSELP_LPC3 ], BIT3 ) ) crcin |= BIT1;
    if( TEST_BIT( vselp[ VSELP_LPC1 ], BIT3 ) ) crcin |= BIT2;
    if( TEST_BIT( vselp[ VSELP_LPC2 ], BIT3 ) ) crcin |= BIT3;
    if( TEST_BIT( vselp[ VSELP_LPC4 ], BIT3 ) ) crcin |= BIT4;
    if( TEST_BIT( vselp[ VSELP_LPC1 ], BIT4 ) ) crcin |= BIT5;
    if( TEST_BIT( vselp[ VSELP_LPC3 ], BIT4 ) ) crcin |= BIT6;
    if( TEST_BIT( vselp[ VSELP_LPC2 ], BIT4 ) ) crcin |= BIT7;
    if( TEST_BIT( vselp[ VSELP_R0 ],   BIT2 ) ) crcin |= BIT8; 
    if( TEST_BIT( vselp[ VSELP_LPC1 ], BIT5 ) ) crcin |= BIT9;
    if( TEST_BIT( vselp[ VSELP_R0 ],   BIT3 ) ) crcin |= BIT10;
    if( TEST_BIT( vselp[ VSELP_R0 ],   BIT4 ) ) crcin |= BIT11;


   /* Apply generator polynomial to CRC bits to generate CRC */
   
    mask    =  (long unsigned)0x00040000L;
    remain  = crcin << 7;
    crcseed =  (long unsigned)0x0005b800L;

    for(i = 0; i < 12; i++)
    {
        if( remain & mask ) remain ^= crcseed;
        mask    >>= 1;
        crcseed >>= 1;
    }

   /* Update CRC field in VSELP parameter array */
   
    vselp[ VSELP_CRC ] = (unsigned)remain;
    return;
}