/* tapi.c - interpolated tap output of a delay line */double tap();double tapi(D, w, p, d)                   /* usage: sd = tapi(D, w, p, d); */double *w, *p, d;                         /* \(d\) = desired non-integer delay */int D;                                    /* \(p\) = circular pointer to \(w\) */{       int i, j;       double si, sj;       i = (int) d;                       /* interpolate between \(s\sb{i}\) and \(s\sb{j}\) */       j = (i+1) % (D+1);                 /* if \(i=D\), then \(j=0\); otherwise, \(j=i+1\) */       si = tap(D, w, p, i);              /* note, \(s\sb{i}(n) = x(n-i)\) */       sj = tap(D, w, p, j);              /* note, \(s\sb{j}(n) = x(n-j)\) */       return si + (d - i) * (sj - si);}