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hammingenc.c
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hammingenc.c
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
void usage(void) {
printf("Usage: hammingenc (takes input from stdin and outputs to stdout)\n");
exit(1);
}
#define DATA_VALUES 16
#define CODE_VALUES 128
/* Tables from hamming library of Michael Dipperstein */
/* table of Hamming codes hammingCodes[x] is the x encoded */
const unsigned char hammingCodes[DATA_VALUES] =
{
0x00, /* 0 */
0x71, /* 1 */
0x62, /* 2 */
0x13, /* 3 */
0x54, /* 4 */
0x25, /* 5 */
0x36, /* 6 */
0x47, /* 7 */
0x38, /* 8 */
0x49, /* 9 */
0x5A, /* A */
0x2B, /* B */
0x6C, /* C */
0x1D, /* D */
0x0E, /* E */
0x7F /* F */
};
/* table convering encoded value (with error) to original data */
/* hammingDecodeValues[code] = original data */
const unsigned char hammingDecodeValues[CODE_VALUES] =
{
0x00, 0x00, 0x00, 0x03, 0x00, 0x05, 0x0E, 0x07, /* 0x00 to 0x07 */
0x00, 0x09, 0x0E, 0x0B, 0x0E, 0x0D, 0x0E, 0x0E, /* 0x08 to 0x0F */
0x00, 0x03, 0x03, 0x03, 0x04, 0x0D, 0x06, 0x03, /* 0x10 to 0x17 */
0x08, 0x0D, 0x0A, 0x03, 0x0D, 0x0D, 0x0E, 0x0D, /* 0x18 to 0x1F */
0x00, 0x05, 0x02, 0x0B, 0x05, 0x05, 0x06, 0x05, /* 0x20 to 0x27 */
0x08, 0x0B, 0x0B, 0x0B, 0x0C, 0x05, 0x0E, 0x0B, /* 0x28 to 0x2F */
0x08, 0x01, 0x06, 0x03, 0x06, 0x05, 0x06, 0x06, /* 0x30 to 0x37 */
0x08, 0x08, 0x08, 0x0B, 0x08, 0x0D, 0x06, 0x0F, /* 0x38 to 0x3F */
0x00, 0x09, 0x02, 0x07, 0x04, 0x07, 0x07, 0x07, /* 0x40 to 0x47 */
0x09, 0x09, 0x0A, 0x09, 0x0C, 0x09, 0x0E, 0x07, /* 0x48 to 0x4F */
0x04, 0x01, 0x0A, 0x03, 0x04, 0x04, 0x04, 0x07, /* 0x50 to 0x57 */
0x0A, 0x09, 0x0A, 0x0A, 0x04, 0x0D, 0x0A, 0x0F, /* 0x58 to 0x5F */
0x02, 0x01, 0x02, 0x02, 0x0C, 0x05, 0x02, 0x07, /* 0x60 to 0x67 */
0x0C, 0x09, 0x02, 0x0B, 0x0C, 0x0C, 0x0C, 0x0F, /* 0x68 to 0x6F */
0x01, 0x01, 0x02, 0x01, 0x04, 0x01, 0x06, 0x0F, /* 0x70 to 0x77 */
0x08, 0x01, 0x0A, 0x0F, 0x0C, 0x0F, 0x0F, 0x0F /* 0x78 to 0x7F */
};
int main(int argc, char **argv)
{
int len,i,inval,outval;
char in[4];
char out[7];
if (argc>1) usage();
if (strstr(argv[0],"hammingenc"))
{ // codifica 4 bits en 7 hamming bits
while((len=fread(&in,1,4,stdin))==4) {
/* encode input bits */
inval=0;
for (i=0;i<4;i++)
if (in[i]=='1') inval+=1<<i;
/* hamming */
outval=hammingCodes[inval];
/* encode output bits */
for (i=0;i<7;i++)
if (outval & (1<<i)) out[i]='1';
else out[i]='0';
if ((len=write(1,&out,7)) !=7)
fprintf(stderr,"Error: write\n");
}
}
else {// decodifica un bloomfilter en un canal
while((len=fread(out,1,7,stdin))==7) {
/* encode input bits */
outval=0;
for (i=0;i<7;i++)
if (out[i]=='1') outval+=1<<i;
/* hamming */
inval= hammingDecodeValues[outval];
/* encode output bits */
for (i=0;i<4;i++)
if (inval & (1<<i)) in[i]='1';
else in[i]='0';
if ((len=write(1,&in,4)) !=4)
fprintf(stderr,"Error: write\n");
}
}
return 0;
}