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/* file: ccoding_byte.c
purpose: Encoding routines for implementing 802.11 convolutionally-coded waveforms
author: raymond.knopp@eurecom.fr, based on similar code for 3GPP convolutional code (UMTS) by P. Humblet (2000)
date: 10.2004
*/
#include "defs.h"
unsigned short gdot11[] = { 0133, 0171 }; // {A,B}
unsigned short gdot11_rev[] = { 0155, 0117 }; // {A,B}
unsigned char ccodedot11_table[128];
unsigned char ccodedot11_table_rev[128];
/*************************************************************************
Encodes for an arbitrary convolutional code of rate 1/2
with a constraint length of 7 bits.
The inputs are bit packed in octets (from MSB to LSB).
Trellis termination is included here
*************************************************************************/
void
ccodedot11_encode (unsigned int numbytes,
unsigned char *inPtr,
unsigned char *outPtr,
unsigned char puncturing)
{
unsigned int state;
unsigned char c, out, shiftbit =0;
// printf("In ccodedot11_encode (%d,%p,%p,%d)\n",numbytes,inPtr,outPtr,puncturing);
#ifdef DEBUG_CCODE
unsigned int dummy;
#endif //DEBUG_CCODE
int bit_index;
/* The input bit is shifted in position 8 of the state.
Shiftbit will take values between 1 and 8 */
state = 0;
#ifdef DEBUG_CCODE
dummy = 0;
#endif //DEBUG_CCODE
/* Do not increment inPtr until we read the next octet */
bit_index=0;
while (numbytes-- > 0) {
c = *inPtr++;
#ifdef DEBUG_CCODE
printf("** %d **\n",c);
#endif //DEBUG_CCODE
switch (puncturing) {
case 0: //rate 1/2
for (shiftbit = 0; shiftbit<8;shiftbit++) {
state >>= 1;
if ((c&(1<<shiftbit)) != 0){
state |= 64;
}
out = ccodedot11_table[state];
*outPtr++ = out & 1;
*outPtr++ = (out>>1)&1;
#ifdef DEBUG_CCODE
printf("%d: %d -> %d (%d)\n",dummy,state,out,ccodedot11_table[state]);
dummy+=2;
#endif //DEBUG_CCODE
}
break;
case 1: // rate 3/4
for (shiftbit = 0; shiftbit<8;shiftbit++) {
state >>= 1;
if ((c&(1<<shiftbit)) != 0){
state |= 64;
}
out = ccodedot11_table[state];
if (bit_index<2)
*outPtr++ = out & 1;
if (bit_index!=1)
*outPtr++ = (out>>1)&1;
#ifdef DEBUG_CCODE
printf("%d: %d -> %d (%d)\n",dummy,state,out,ccodedot11_table[state]);
dummy+=2;
#endif //DEBUG_CCODE
bit_index=(bit_index==2)?0:(bit_index+1);
}
break;
case 2: // rate 2/3
for (shiftbit = 0; shiftbit<8;shiftbit++) {
state >>= 1;
if ((c&(1<<shiftbit)) != 0){
state |= 64;
}
out = ccodedot11_table[state];
*outPtr++ = out & 1;
if (bit_index==0)
*outPtr++ = (out>>1)&1;
#ifdef DEBUG_CCODE
printf("%d: %d -> %d (%d)\n",dummy,state,out,ccodedot11_table[state]);
dummy+=2;
#endif //DEBUG_CCODE
bit_index=(bit_index==0)?1:0;
}
break;
default:
break;
}
}
/*
// Termination - Add one NULL byte to terminate trellis
#ifdef DEBUG_CCODE
printf("Termination\n");
#endif //DEBUG_CCODE
for (shiftbit = 0; shiftbit<8;shiftbit++) {
state >>= 1;
out = ccodedot11_table[state];
*outPtr++ = out & 1;
*outPtr++ = (out>>1)&1;
#ifdef DEBUG_CCODE
printf("%d: %d -> %d (%d)\n",dummy,state,out,ccodedot11_table[state]);
dummy+=2;
#endif //DEBUG_CCODE
printf("%d -> %d (%d)\n",state,out,ccodedot11_table[state]);
}
*/
}
/*************************************************************************
Functions to initialize the code tables
*************************************************************************/
/* Basic code table initialization for constraint length 7 */
/* Input in MSB, followed by state in 6 LSBs */
void ccodedot11_init(void)
{
unsigned int i, j, k, sum;
for (i = 0; i < 128; i++) {
ccodedot11_table[i] = 0;
/* Compute R output bits */
for (j = 0; j < 2; j++) {
sum = 0;
for (k = 0; k < 7; k++)
if ((i & gdot11[j]) & (1 << k))
sum++;
/* Write the sum modulo 2 in bit j */
ccodedot11_table[i] |= (sum & 1) << j;
}
}
}
/* Input in LSB, followed by state in 6 MSBs */
void ccodedot11_init_inv(void)
{
unsigned int i, j, k, sum;
for (i = 0; i < 128; i++) {
ccodedot11_table_rev[i] = 0;
/* Compute R output bits */
for (j = 0; j < 2; j++) {
sum = 0;
for (k = 0; k < 7; k++)
if ((i & gdot11_rev[j]) & (1 << k))
sum++;
/* Write the sum modulo 2 in bit j */
ccodedot11_table_rev[i] |= (sum & 1) << j;
}
}
}
/*****************************************************************/
/**
Test program
******************************************************************/
#ifdef DEBUG_CCODE
#include <stdio.h>
main()
{
unsigned char test[] = "0Thebigredfox";
unsigned char output[512], *inPtr, *outPtr;
unsigned int i;
test[0] = 128;
test[1] = 0;
ccodedot11_init();
inPtr = test;
outPtr = output;
ccodedot11_encode(16, inPtr, outPtr,0);
for (i = 0; i < 32; i++) printf("%x ", output[i]);
printf("\n");
}
#endif
/** @}*/