equalize.c

Fax and soft modem library source code.

/* Modem for MIPS   AJF	  October 1996
   Equalizer routines */

#include <stdio.h>
#include <string.h>

#include "private.h"
#include "complex.h"
#include "equalize.h"


void equalizer::reset()
  { for (int i = 0; i < 2*np+1; i++) coeffs[i] = 0.0;
    coeffs[np] = 1.0;
    for (int i = 0; i < size; i++) in[i] = 0.0;
    next = 0;
  }

void equalizer::insert(complex z)
  { /* circular buffer */
    in[next] = z;
    if (++next >= size) next = 0;
  }

complex equalizer::get()
  { /* get equalized value */
    complex z = 0.0; int ncs = 2*np+1;
    for (int i = 0; i < ncs; i++)
      { int p = (next+i) & (size-1);
	z += coeffs[i] * in[p];
      }
    return z;
  }

void equalizer::upd(complex eps, int n)
  { complex deps = (delta / (2*n+1)) * eps;
    for (int i = np-n; i <= np+n; i++)
      { int p = (next+i) & (size-1);
	coeffs[i] += deps * cconj(in[p]);
      }
  }

int equalizer::getdt()
  { int k1 = 0, k2 = 2*np;
    float p1 = 0.0, p2 = 0.0;	/* total power to left of k1, right of k2 */
    while (k1 < k2)
      { if (p1 > p2) p2 += power(coeffs[k2--]);
	else p1 += power(coeffs[k1++]);
      }
    return k1-np;	/* return timing (sample point) error, in units of half a symbol */
  }

void equalizer::shift(int dt)
  { int ncs = 2*np+1;
    if (dt > 0)
      { memmove(&coeffs[dt], &coeffs[0], (ncs-dt) * sizeof(complex));
	memset(&coeffs[0], 0, dt * sizeof(complex));
      }
    if (dt < 0)
      { dt = -dt;
	memmove(&coeffs[0], &coeffs[dt], (ncs-dt) * sizeof(complex));
	memset(&coeffs[ncs-dt], 0, dt * sizeof(complex));
      }
  }

void equalizer::print(char *fn)
  { FILE *fi = fopen(fn, "w");
    if (fi != NULL)
      { fprintf(fi, ".sp 0.5i\n.G1 8i\n");
	fprintf(fi, "new solid\n");
	for (int j = -np; j <= +np; j++) fprintf(fi, "%d %g\n", j, coeffs[np+j].re);
	fprintf(fi, "new dashed\n");
	for (int j = -np; j <= +np; j++) fprintf(fi, "%d %g\n", j, coeffs[np+j].im);
	fprintf(fi, "new dotted\n");
	for (int j = -np; j <= +np; j++) fprintf(fi, "%d %g\n", j, power(coeffs[np+j]));
	fprintf(fi, ".G2\n.bp\n");
	for (int j = -np; j <= +np; j++) fprintf(fi, "{ %10.6f, %10.6f },\n", coeffs[np+j].re, coeffs[np+j].im);
	fclose(fi);
      }
    else fprintf(stderr, "can't create %s\n", fn);
  }