/* cfir.c - FIR filter implemented with circular delay-line buffer */void wrap();double cfir(M, h, w, p, x)double *h, *w, **p, x;                         /* \(p\) = circular pointer to \(w\) */int M;                                         /* \(M\) = filter order */{                               int i;       double y;       **p = x;                                /* read input sample \(x\) */       for (y=0, i=0; i<=M; i++) {             /* compute output sample \(y\) */              y += (*h++) * (*(*p)++);              wrap(M, w, p);              }       (*p)--;                                 /* update circular delay line */       wrap(M, w, p);       return y;}