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//
// interleaver_scatterplot_example.c
//
// generate interleaver scatterplot figure
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <assert.h>
#include "liquid.h"
#define OUTPUT_FILENAME "interleaver_scatterplot_example.m"
// print usage/help message
void usage()
{
printf("interleaver_scatterplot_example [options]\n");
printf(" u/h : print usage\n");
printf(" n : number of bytes, default: 8\n");
printf(" d : interleaver depth, default: 4\n");
}
// find most significant bit in array (starting from left)
unsigned int interleaver_find_bit(unsigned char * _x,
unsigned int _n);
int main(int argc, char*argv[]) {
// options
unsigned int n=8; // message length
unsigned int depth = 4;
int dopt;
while ((dopt = getopt(argc,argv,"uhn:d:")) != EOF) {
switch (dopt) {
case 'u':
case 'h': usage(); return 0;
case 'n': n = atoi(optarg); break;
case 'd': depth = atoi(optarg); break;
default:
exit(1);
}
}
// create the interleaver
interleaver q = interleaver_create(n);
interleaver_set_depth(q, depth);
// create arrays
unsigned char x[n]; // original message data
unsigned char y[n]; // interleaved data
unsigned int index[8*n];
unsigned int i;
unsigned int j;
unsigned int k=0;
// initialize data
memset(x, 0, n*sizeof(unsigned char));
for (i=0; i<n; i++) {
for (j=0; j<8; j++) {
x[i] = 1 << (8-j-1);
// run interleaver and find most significant
// bit in resulting array
interleaver_encode(q,x,y);
index[k] = interleaver_find_bit(y,n);
// increment index counter
k++;
}
// reset input message sequence
x[i] = 0;
}
assert(k==8*n);
// destroy the interleaver object
interleaver_destroy(q);
// write output file
FILE * fid = fopen(OUTPUT_FILENAME,"w");
if (fid == NULL) {
fprintf(stderr,"error: %s, could not open file '%s' for writing.\n", argv[0],OUTPUT_FILENAME);
exit(1);
}
// print header
fprintf(fid,"%% %s : auto-generated file (do not edit)\n", OUTPUT_FILENAME);
fprintf(fid,"%% invoked as :");
for (i=0; i<argc; i++)
fprintf(fid," %s",argv[i]);
fprintf(fid,"\n");
fprintf(fid,"clear all\n");
fprintf(fid,"close all\n");
fprintf(fid,"n = %u;\n", 8*n);
// export data to file
for (i=0; i<8*n; i++)
fprintf(fid,"index(%6u) = %6u;\n", i+1, index[i]);
fprintf(fid,"figure;\n");
fprintf(fid,"i = [0:(n-1)];\n");
fprintf(fid,"plot(i/n,index/n,'x');\n");
fprintf(fid,"axis square\n");
fprintf(fid,"axis([0 1 0 1]);\n");
// close it up
fclose(fid);
printf("results written to '%s'\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
// find most significant bit in array (starting from left)
unsigned int interleaver_find_bit(unsigned char * _x,
unsigned int _n)
{
unsigned int i;
for (i=0; i<_n; i++) {
if (_x[i] != 0)
break;
}
unsigned char byte = _x[i];
// find most significant bit in byte
switch (byte) {
case (1<<7): return 8*i + 0; // 1000 0000
case (1<<6): return 8*i + 1; // 0100 0000
case (1<<5): return 8*i + 2; // 0010 0000
case (1<<4): return 8*i + 3; // 0001 0000
case (1<<3): return 8*i + 4; // 0000 1000
case (1<<2): return 8*i + 5; // 0000 0100
case (1<<1): return 8*i + 6; // 0000 0010
case (1<<0): return 8*i + 7; // 0000 0001
default:
fprintf(stderr,"error: interleaver_find_bid(), invalid array\n");
exit(1);
}
}
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