Lsp.java

/* -*-mode:java; c-basic-offset:2; indent-tabs-mode:nil -*- */
/* JOrbis
 * Copyright (C) 2000 ymnk, JCraft,Inc.
 *  
 * Written by: 2000 ymnk<ymnk@jcraft.com>
 *   
 * Many thanks to 
 *   Monty <monty@xiph.org> and 
 *   The XIPHOPHORUS Company http://www.xiph.org/ .
 * JOrbis has been based on their awesome works, Vorbis codec.
 *   
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License
 * as published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
   
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package com.jcraft.jorbis;

/*
  function: LSP (also called LSF) conversion routines

  The LSP generation code is taken (with minimal modification) from
  "On the Computation of the LSP Frequencies" by Joseph Rothweiler
  <rothwlr@altavista.net>, available at:
  
  http://www2.xtdl.com/~rothwlr/lsfpaper/lsfpage.html 
 ********************************************************************/

class Lsp {

    static final float M_PI = (float) (3.1415926539);

    static void lsp_to_curve(float[] curve, int[] map, int n, int ln,
                             float[] lsp, int m, float amp, float ampoffset) {
        int i;
        float wdel = M_PI / ln;
        for (i = 0; i < m; i++)
            lsp[i] = Lookup.coslook(lsp[i]);
        int m2 = (m / 2) * 2;

        i = 0;
        while (i < n) {
            int k = map[i];
            float p = .7071067812f;
            float q = .7071067812f;
            float w = Lookup.coslook(wdel * k);

            for (int j = 0; j < m2; j += 2) {
                q *= lsp[j] - w;
                p *= lsp[j + 1] - w;
            }

            if ((m & 1) != 0) {
                /* odd order filter; slightly assymetric */
                /* the last coefficient */
                q *= lsp[m - 1] - w;
                q *= q;
                p *= p * (1.f - w * w);
            } else {
                /* even order filter; still symmetric */
                q *= q * (1.f + w);
                p *= p * (1.f - w);
            }

            //  q=frexp(p+q,&qexp);
            q = p + q;
            int hx = Float.floatToIntBits(q);
            int ix = 0x7fffffff & hx;
            int qexp = 0;

            if (ix >= 0x7f800000 || (ix == 0)) {
                // 0,inf,nan
            } else {
                if (ix < 0x00800000) { // subnormal
                    q *= 3.3554432000e+07; // 0x4c000000
                    hx = Float.floatToIntBits(q);
                    ix = 0x7fffffff & hx;
                    qexp = -25;
                }
                qexp += ((ix >>> 23) - 126);
                hx = (hx & 0x807fffff) | 0x3f000000;
                q = Float.intBitsToFloat(hx);
            }

            q = Lookup.fromdBlook(amp * Lookup.invsqlook(q) * Lookup.invsq2explook(qexp + m)
                    - ampoffset);

            do {
                curve[i++] *= q;
            }
            while (i < n && map[i] == k);

        }
    }
}