1 /*************************************************************************/
2 /* */
3 /* Centre for Speech Technology Research */
4 /* University of Edinburgh, UK */
5 /* Copyright (c) 1996,1997 */
6 /* All Rights Reserved. */
7 /* */
8 /* Permission is hereby granted, free of charge, to use and distribute */
9 /* this software and its documentation without restriction, including */
10 /* without limitation the rights to use, copy, modify, merge, publish, */
11 /* distribute, sublicense, and/or sell copies of this work, and to */
12 /* permit persons to whom this work is furnished to do so, subject to */
13 /* the following conditions: */
14 /* 1. The code must retain the above copyright notice, this list of */
15 /* conditions and the following disclaimer. */
16 /* 2. Any modifications must be clearly marked as such. */
17 /* 3. Original authors' names are not deleted. */
18 /* 4. The authors' names are not used to endorse or promote products */
19 /* derived from this software without specific prior written */
20 /* permission. */
21 /* */
22 /* THE UNIVERSITY OF EDINBURGH AND THE CONTRIBUTORS TO THIS WORK */
23 /* DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING */
24 /* ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT */
25 /* SHALL THE UNIVERSITY OF EDINBURGH NOR THE CONTRIBUTORS BE LIABLE */
26 /* FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES */
27 /* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN */
28 /* AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, */
29 /* ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF */
30 /* THIS SOFTWARE. */
31 /* */
32 /*************************************************************************/
33 /* Author : Steve Isard */
34 /* Date : 1984 */
35 /* This version was gifted by Steve for this new */
36 /* copyright, the original retains their original copyright */
37 /* */
38 /*************************************************************************/
39 #include <math.h>
40 #include <stdio.h>
41 #include "t2s.h"
42
43 /* transform a set of reflection coefficients to linear prediction
44 * coefficients using algorithm from HCL-H
45 */
46
rfctolpc(float * buf)47 void rfctolpc(float *buf)
48 {
49 float a,b;
50 register float *cptr;
51 register int n,k;
52
53 /* HCL-H algorithm goes through coeffs in reverse of order in which they
54 * appear here, working on buffer numbered from 1 upwards. To get same
55 * effect, we make cptr point at space just after last coeff and let n and
56 * k go down from -1 instead of up from 1.
57 */
58 cptr = buf + NCOEFFS; /* There should be NCOEFFS coeffs. Point just
59 * after last one.
60 */
61
62 for(n = -1; n >= -NCOEFFS; n--) {
63 *(cptr+n) = -(*(cptr+n));
64 for(k = -1; 2*k >= n; k--) {
65 a = *(cptr+k);
66 b = *(cptr+n-k);
67 *(cptr+k) = a - b * *(cptr+n);
68 *(cptr+n-k) = b - a * *(cptr+n);
69 }
70 }
71 }
72
73