Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet

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SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]

11063K–ATARM–05-Nov-13

{

/* galois inverse */

sro[k] = gf_antilog[(gf_log[dmu[i]] + (NB_FIELD_ELEMENTS-

gf_log[dmu[ro]]) + gf_log[sro[k]]) % NB_FIELD_ELEMENTS];

}

}

/* multiply by dmu * dmu[ro]^-1 */

for (k = 0; k < 2*NB_ERROR_MAX+1; k++)

{

smu[i+1][k] = smu[i][k] ^ sro[k];

if (smu[i+1][k])

{

/* find the order of the polynom */

lmu[i+1] = k << 1; 

}

}

}

/*                                               */

/*                                               */

/*      End Compute Sigma (Mu+1)                 */

/*      And L(mu)                                */

/*************************************************/

/* In either case compute delta */

delta[i+1]  = (mu[i+1] * 2 - lmu[i+1]) >> 1;

/* In either case compute the discrepancy */

for (k = 0 ; k <= (lmu[i+1]>>1); k++)

{

if (k == 0)

dmu[i+1] = si[2*(i-1)+3];

/* check if one operand of the multiplier is null, its index is -1 */

else if (smu[i+1][k] && si[2*(i-1)+3-k])

dmu[i+1] = gf_antilog[(gf_log[smu[i+1][k]] + gf_log[si[2*(i-1)+3-k]])%nn] 

^ dmu[i+1];

}

}

return 0;

}

The output of the get_sigma() procedure is a polynomial stored in the smu[NB_ERROR+1][] table. The error position is
the roots of that polynomial. The degree of this polynomial is very important information, as it gives the number of errors.
The PMERRLOC module provides a hardware accelerator for this step.