sinegen.c

Fax and soft modem library source code.

/* Modem for MIPS   AJF	  January 1995
   Sine generator */

#include <stdio.h>
#include <math.h>

#include "private.h"
#include "complex.h"
#include "sinegen.h"
#include "myaudio.h"

#define SLENK	11 // ??? was 15
#define SINELEN (1 << SLENK)
#define TWO32	4.294967296e9	/* 2^32 */
#define TWOPI	(2.0 * M_PI)

static struct Init_Sines
  { Init_Sines();
  }
init_sines;

static float *sinetab;

Init_Sines::Init_Sines()
  { /* once-only initialization, done before main() is called */
    sinetab = new float[SINELEN];
    if (sinetab == NULL)
      { fprintf(stderr, "No room! Init_Sines\r\n");
	exit(1);
      }
    for (int k = 0; k < SINELEN; k++)
      { float th = TWOPI * (float) k / (float) SINELEN;
	sinetab[k] = sin(th);
      }
  }

sinegen::sinegen(float f)
  { setfreq(f);
    resetphase();
  }

void sinegen::setfreq(float f)
  { phinc = (int) (f * TWO32 / (float) SAMPLERATE);
  }

float sinegen::fnext()
  { float x = sinetab[ptr >> (32-SLENK)];	/* keep top SLENK bits */
    ptr += phinc;
    return x;
  }

complex sinegen::cnext()
  { complex z = complex(sinetab[ptr >> (32-SLENK)],
			sinetab[(ptr + (1 << 30)) >> (32-SLENK)]);
    ptr += phinc;
    return z;
  }