This is unconvert.c in view mode; [Download] [Up]
#include "pv.h"
/*
* unconvert essentially undoes what convert does, i.e., it
* turns N2+1 PAIRS of amplitude and frequency values in
* C into N2 PAIR of complex spectrum data (in rfft format)
* in output array S; sampling rate R and interpolation factor
* I are used to recompute phase values from frequencies
*/
unconvert( C, S, N2, I, R )
float C[], S[] ; int N2, I, R ;
{
static int first = 1 ;
static float *lastphase, fundamental, factor ;
int i, real, imag, amp, freq ;
float mag, phase ;
/*
* FIRST TIME ONLY: allocate memory and compute constants
*/
if ( first ) {
first = 0 ;
fvec( lastphase, N2+1 ) ;
fundamental = (float) R/(N2<<1) ;
factor = TWOPI*I/R ;
}
/*
* subtract out frequencies associated with each channel,
* compute phases in terms of radians per I samples, and
* convert to complex form
*/
for ( i = 0 ; i <= N2 ; i++ ) {
imag = freq = ( real = amp = i<<1 ) + 1 ;
if ( i == N2 )
real = 1 ;
mag = C[amp] ;
lastphase[i] += C[freq] - i*fundamental ;
phase = lastphase[i]*factor ;
S[real] = mag*cos( phase ) ;
if ( i != N2 )
S[imag] = -mag*sin( phase ) ;
}
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.