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#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "rs.h"
extern unsigned int KK;
unsigned int
rs_kkcompute (unsigned int n, unsigned int fix);
void
rs_trans (unsigned char *buffer, unsigned long int buf_len,
unsigned int *trans, unsigned long int trans_len);
void
rs_detrans (unsigned char *buffer, unsigned long int buf_len,
unsigned int *trans, unsigned long int trans_len);
int
main (int argc, char *argv[])
{
int n;
unsigned char buffer[6144];
unsigned int transform[4096];
memset (buffer, '\0', sizeof (buffer));
strcpy (buffer, "This is a test for the Reed Solomon encoder/decoder");
printf ("before: %s\n", buffer);
rs_trans (buffer, strlen (buffer), transform, sizeof (transform) /
sizeof (transform[0]));
memset (buffer, '\0', sizeof (buffer));
KK = rs_kkcompute (NN, (36 * 8) / 12 + 1);
encode_rs (&transform[0], &transform[KK]);
srandom (time (NULL));
for (n = 0 ; n < 25 ; ++n) {
unsigned int ai;
do {
ai = random () % KK;
} while ((transform[ai] & 0x1000) == 0x1000);
transform[ai] = (random () & 0x0fff) | 0x1000;
}
for (n = 0 ; n < KK ; ++n)
transform[n] &= ~ 0x1000;
// printf (" trash: %s\n", buffer);
n = eras_dec_rs (transform, NULL, 0);
rs_detrans (buffer, sizeof (buffer), transform, sizeof (transform) /
sizeof (transform[0]));
printf ("c (%2d): %s\n", n, buffer);
exit (EXIT_SUCCESS);
}
/* rs_kkcompute
*
* for our fingerprint deviation method we need to go the reverse way in error
* correction. instead of trying to find the optimum signal-noise/correction
* ratio, we know exactly how many bytes we want to fix and can guarantee a
* perfect reliability for our parity check bits. so this is the function that
* computes the correct KK value for `n' symbols, where we want to be able to
* fixup up to `fix' symbols.
*
* return the correct value for KK
*/
unsigned int
rs_kkcompute (unsigned int n, unsigned int fix)
{
/* assume sanity of all input values */
return (n - (2 * fix));
}
void
rs_trans (unsigned char *buffer, unsigned long int buf_len,
unsigned int *trans, unsigned long int trans_len)
{
unsigned int n,
t;
memset (trans, '\0', sizeof (trans[0]) * trans_len);
if (((((buf_len + 1) * 12) / 8)) > trans_len) {
fprintf (stderr, "translation output size too low\n");
exit (EXIT_FAILURE);
}
/* 8 to 12 bit expander to use 2^12 galois field */
for (n = 0, t = 0 ; n < buf_len ; ++n) {
switch (n % 3) {
case (0):
trans[t] = buffer[n];
break;
case (1):
trans[t] |= (buffer[n] & 0x0f) << 8;
trans[t + 1] = buffer[n] >> 4;
t += 1;
break;
case (2):
trans[t] |= buffer[n] << 4;
t += 1;
break;
}
}
return;
}
/* and the reverse (12 to 8 bit)
*/
void
rs_detrans (unsigned char *buffer, unsigned long int buf_len,
unsigned int *trans, unsigned long int trans_len)
{
unsigned int n,
t;
memset (buffer, '\0', buf_len);
if (((trans_len * 12) / 8) > buf_len) {
fprintf (stderr, "translation output buffer too low\n");
exit (EXIT_FAILURE);
}
for (n = 0, t = 0 ; t < trans_len ; ++t) {
switch (t % 2) {
case (0):
buffer[n] = trans[t] & 0xff;
buffer[n + 1] = trans[t] >> 8;
n += 1;
break;
case (1):
buffer[n] |= (trans[t] & 0x0f) << 4;
buffer[n + 1] = trans[t] >> 4;
n += 2;
break;
}
}
return;
}
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