summaryrefslogtreecommitdiffstats
path: root/apps/codecs/libspeex/lsp.c
blob: fcc12515c3604634c573adf537196135533345c8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
/*---------------------------------------------------------------------------*\
Original copyright
	FILE........: lsp.c
	AUTHOR......: David Rowe
	DATE CREATED: 24/2/93

Heavily modified by Jean-Marc Valin (c) 2002-2006 (fixed-point, 
                       optimizations, additional functions, ...)

   This file contains functions for converting Linear Prediction
   Coefficients (LPC) to Line Spectral Pair (LSP) and back. Note that the
   LSP coefficients are not in radians format but in the x domain of the
   unit circle.

   Speex License:

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:
   
   - Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
   
   - Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
   
   - Neither the name of the Xiph.org Foundation nor the names of its
   contributors may be used to endorse or promote products derived from
   this software without specific prior written permission.
   
   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*---------------------------------------------------------------------------*\

  Introduction to Line Spectrum Pairs (LSPs)
  ------------------------------------------

  LSPs are used to encode the LPC filter coefficients {ak} for
  transmission over the channel.  LSPs have several properties (like
  less sensitivity to quantisation noise) that make them superior to
  direct quantisation of {ak}.

  A(z) is a polynomial of order lpcrdr with {ak} as the coefficients.

  A(z) is transformed to P(z) and Q(z) (using a substitution and some
  algebra), to obtain something like:

    A(z) = 0.5[P(z)(z+z^-1) + Q(z)(z-z^-1)]  (1)

  As you can imagine A(z) has complex zeros all over the z-plane. P(z)
  and Q(z) have the very neat property of only having zeros _on_ the
  unit circle.  So to find them we take a test point z=exp(jw) and
  evaluate P (exp(jw)) and Q(exp(jw)) using a grid of points between 0
  and pi.

  The zeros (roots) of P(z) also happen to alternate, which is why we
  swap coefficients as we find roots.  So the process of finding the
  LSP frequencies is basically finding the roots of 5th order
  polynomials.

  The root so P(z) and Q(z) occur in symmetrical pairs at +/-w, hence
  the name Line Spectrum Pairs (LSPs).

  To convert back to ak we just evaluate (1), "clocking" an impulse
  thru it lpcrdr times gives us the impulse response of A(z) which is
  {ak}.

\*---------------------------------------------------------------------------*/

#ifdef HAVE_CONFIG_H
#include "config-speex.h"
#endif

#include <math.h>
#include "lsp.h"
#include "stack_alloc.h"
#include "math_approx.h"

#ifndef M_PI
#define M_PI           3.14159265358979323846  /* pi */
#endif

#ifndef NULL
#define NULL 0
#endif

#ifdef FIXED_POINT

#define FREQ_SCALE 16384

/*#define ANGLE2X(a) (32768*cos(((a)/8192.)))*/
#define ANGLE2X(a) (SHL16(spx_cos(a),2))

/*#define X2ANGLE(x) (acos(.00006103515625*(x))*LSP_SCALING)*/
#define X2ANGLE(x) (spx_acos(x))

#ifdef BFIN_ASM
#include "lsp_bfin.h"
#endif

#else

/*#define C1 0.99940307
#define C2 -0.49558072
#define C3 0.03679168*/

#define FREQ_SCALE 1.
#define ANGLE2X(a) (spx_cos(a))
#define X2ANGLE(x) (acos(x))

#endif


/*---------------------------------------------------------------------------*\

   FUNCTION....: cheb_poly_eva()

   AUTHOR......: David Rowe
   DATE CREATED: 24/2/93

   This function evaluates a series of Chebyshev polynomials

\*---------------------------------------------------------------------------*/

#ifdef FIXED_POINT

#ifndef OVERRIDE_CHEB_POLY_EVA
static inline spx_word32_t cheb_poly_eva(
  spx_word16_t *coef, /* P or Q coefs in Q13 format               */
  spx_word16_t     x, /* cos of freq (-1.0 to 1.0) in Q14 format  */
  int              m, /* LPC order/2                              */
  char         *stack
)
{
    int i;
    spx_word16_t b0, b1;
    spx_word32_t sum;

    /*Prevents overflows*/
    if (x>16383)
       x = 16383;
    if (x<-16383)
       x = -16383;

    /* Initialise values */
    b1=16384;
    b0=x;

    /* Evaluate Chebyshev series formulation usin g iterative approach  */
    sum = ADD32(EXTEND32(coef[m]), EXTEND32(MULT16_16_P14(coef[m-1],x)));
    for(i=2;i<=m;i++)
    {
       spx_word16_t tmp=b0;
       b0 = SUB16(MULT16_16_Q13(x,b0), b1);
       b1 = tmp;
       sum = ADD32(sum, EXTEND32(MULT16_16_P14(coef[m-i],b0)));
    }
    
    return sum;
}
#endif

#else

static float cheb_poly_eva(spx_word32_t *coef, spx_word16_t x, int m, char *stack)
{
   int k;
   float b0, b1, tmp;

   /* Initial conditions */
   b0=0; /* b_(m+1) */
   b1=0; /* b_(m+2) */

   x*=2;

   /* Calculate the b_(k) */
   for(k=m;k>0;k--)
   {
      tmp=b0;                           /* tmp holds the previous value of b0 */
      b0=x*b0-b1+coef[m-k];    /* b0 holds its new value based on b0 and b1 */
      b1=tmp;                           /* b1 holds the previous value of b0 */
   }

   return(-b1+.5*x*b0+coef[m]);
}
#endif

/*---------------------------------------------------------------------------*\

    FUNCTION....: lpc_to_lsp()

    AUTHOR......: David Rowe
    DATE CREATED: 24/2/93

    This function converts LPC coefficients to LSP
    coefficients.

\*---------------------------------------------------------------------------*/

#ifdef FIXED_POINT
#define SIGN_CHANGE(a,b) (((a)&0x70000000)^((b)&0x70000000)||(b==0))
#else
#define SIGN_CHANGE(a,b) (((a)*(b))<0.0)
#endif


int lpc_to_lsp (spx_coef_t *a,int lpcrdr,spx_lsp_t *freq,int nb,spx_word16_t delta, char *stack)
/*  float *a 		     	lpc coefficients			*/
/*  int lpcrdr			order of LPC coefficients (10) 		*/
/*  float *freq 	      	LSP frequencies in the x domain       	*/
/*  int nb			number of sub-intervals (4) 		*/
/*  float delta			grid spacing interval (0.02) 		*/


{
    spx_word16_t temp_xr,xl,xr,xm=0;
    spx_word32_t psuml,psumr,psumm,temp_psumr/*,temp_qsumr*/;
    int i,j,m,flag,k;
    VARDECL(spx_word32_t *Q);                 	/* ptrs for memory allocation 		*/
    VARDECL(spx_word32_t *P);
    VARDECL(spx_word16_t *Q16);         /* ptrs for memory allocation 		*/
    VARDECL(spx_word16_t *P16);
    spx_word32_t *px;                	/* ptrs of respective P'(z) & Q'(z)	*/
    spx_word32_t *qx;
    spx_word32_t *p;
    spx_word32_t *q;
    spx_word16_t *pt;                	/* ptr used for cheb_poly_eval()
				whether P' or Q' 			*/
    int roots=0;              	/* DR 8/2/94: number of roots found 	*/
    flag = 1;                	/*  program is searching for a root when,
				1 else has found one 			*/
    m = lpcrdr/2;            	/* order of P'(z) & Q'(z) polynomials 	*/

    /* Allocate memory space for polynomials */
    ALLOC(Q, (m+1), spx_word32_t);
    ALLOC(P, (m+1), spx_word32_t);

    /* determine P'(z)'s and Q'(z)'s coefficients where
      P'(z) = P(z)/(1 + z^(-1)) and Q'(z) = Q(z)/(1-z^(-1)) */

    px = P;                      /* initialise ptrs 			*/
    qx = Q;
    p = px;
    q = qx;

#ifdef FIXED_POINT
    *px++ = LPC_SCALING;
    *qx++ = LPC_SCALING;
    for(i=0;i<m;i++){
       *px++ = SUB32(ADD32(EXTEND32(a[i]),EXTEND32(a[lpcrdr-i-1])), *p++);
       *qx++ = ADD32(SUB32(EXTEND32(a[i]),EXTEND32(a[lpcrdr-i-1])), *q++);
    }
    px = P;
    qx = Q;
    for(i=0;i<m;i++)
    {
       /*if (fabs(*px)>=32768)
          speex_warning_int("px", *px);
       if (fabs(*qx)>=32768)
       speex_warning_int("qx", *qx);*/
       *px = PSHR32(*px,2);
       *qx = PSHR32(*qx,2);
       px++;
       qx++;
    }
    /* The reason for this lies in the way cheb_poly_eva() is implemented for fixed-point */
    P[m] = PSHR32(P[m],3);
    Q[m] = PSHR32(Q[m],3);
#else
    *px++ = LPC_SCALING;
    *qx++ = LPC_SCALING;
    for(i=0;i<m;i++){
       *px++ = (a[i]+a[lpcrdr-1-i]) - *p++;
       *qx++ = (a[i]-a[lpcrdr-1-i]) + *q++;
    }
    px = P;
    qx = Q;
    for(i=0;i<m;i++){
       *px = 2**px;
       *qx = 2**qx;
       px++;
       qx++;
    }
#endif

    px = P;             	/* re-initialise ptrs 			*/
    qx = Q;

    /* now that we have computed P and Q convert to 16 bits to
       speed up cheb_poly_eval */

    ALLOC(P16, m+1, spx_word16_t);
    ALLOC(Q16, m+1, spx_word16_t);

    for (i=0;i<m+1;i++)
    {
       P16[i] = P[i];
       Q16[i] = Q[i];
    }

    /* Search for a zero in P'(z) polynomial first and then alternate to Q'(z).
    Keep alternating between the two polynomials as each zero is found 	*/

    xr = 0;             	/* initialise xr to zero 		*/
    xl = FREQ_SCALE;               	/* start at point xl = 1 		*/

    for(j=0;j<lpcrdr;j++){
	if(j&1)            	/* determines whether P' or Q' is eval. */
	    pt = Q16;
	else
	    pt = P16;

	psuml = cheb_poly_eva(pt,xl,m,stack);	/* evals poly. at xl 	*/
	flag = 1;
	while(flag && (xr >= -FREQ_SCALE)){
           spx_word16_t dd;
           /* Modified by JMV to provide smaller steps around x=+-1 */
#ifdef FIXED_POINT
           dd = MULT16_16_Q15(delta,SUB16(FREQ_SCALE, MULT16_16_Q14(MULT16_16_Q14(xl,xl),14000)));
           if (psuml<512 && psuml>-512)
              dd = PSHR16(dd,1);
#else
           dd=delta*(1-.9*xl*xl);
           if (fabs(psuml)<.2)
              dd *= .5;
#endif
           xr = SUB16(xl, dd);                        	/* interval spacing 	*/
	    psumr = cheb_poly_eva(pt,xr,m,stack);/* poly(xl-delta_x) 	*/
	    temp_psumr = psumr;
	    temp_xr = xr;

    /* if no sign change increment xr and re-evaluate poly(xr). Repeat til
    sign change.
    if a sign change has occurred the interval is bisected and then
    checked again for a sign change which determines in which
    interval the zero lies in.
    If there is no sign change between poly(xm) and poly(xl) set interval
    between xm and xr else set interval between xl and xr and repeat till
    root is located within the specified limits 			*/

	    if(SIGN_CHANGE(psumr,psuml))
            {
		roots++;

		psumm=psuml;
		for(k=0;k<=nb;k++){
#ifdef FIXED_POINT
		    xm = ADD16(PSHR16(xl,1),PSHR16(xr,1));        	/* bisect the interval 	*/
#else
                    xm = .5*(xl+xr);        	/* bisect the interval 	*/
#endif
		    psumm=cheb_poly_eva(pt,xm,m,stack);
		    /*if(psumm*psuml>0.)*/
		    if(!SIGN_CHANGE(psumm,psuml))
                    {
			psuml=psumm;
			xl=xm;
		    } else {
			psumr=psumm;
			xr=xm;
		    }
		}

	       /* once zero is found, reset initial interval to xr 	*/
	       freq[j] = X2ANGLE(xm);
	       xl = xm;
	       flag = 0;       		/* reset flag for next search 	*/
	    }
	    else{
		psuml=temp_psumr;
		xl=temp_xr;
	    }
	}
    }
    return(roots);
}

/*---------------------------------------------------------------------------*\

	FUNCTION....: lsp_to_lpc()

	AUTHOR......: David Rowe
	DATE CREATED: 24/2/93

        Converts LSP coefficients to LPC coefficients.

\*---------------------------------------------------------------------------*/

#ifdef FIXED_POINT

void lsp_to_lpc(spx_lsp_t *freq,spx_coef_t *ak,int lpcrdr, char *stack)
/*  float *freq 	array of LSP frequencies in the x domain	*/
/*  float *ak 		array of LPC coefficients 			*/
/*  int lpcrdr  	order of LPC coefficients 			*/
{
    int i,j;
    spx_word32_t xout1,xout2,xin;
    spx_word32_t mult, a;
    VARDECL(spx_word16_t *freqn);
    VARDECL(spx_word32_t **xp);
    VARDECL(spx_word32_t *xpmem);
    VARDECL(spx_word32_t **xq);
    VARDECL(spx_word32_t *xqmem);
    int m = lpcrdr>>1;

    /* 
    
       Reconstruct P(z) and Q(z) by cascading second order polynomials
       in form 1 - 2cos(w)z(-1) + z(-2), where w is the LSP frequency.
       In the time domain this is:

       y(n) = x(n) - 2cos(w)x(n-1) + x(n-2)
    
       This is what the ALLOCS below are trying to do:

         int xp[m+1][lpcrdr+1+2]; // P matrix in QIMP
         int xq[m+1][lpcrdr+1+2]; // Q matrix in QIMP

       These matrices store the output of each stage on each row.  The
       final (m-th) row has the output of the final (m-th) cascaded
       2nd order filter.  The first row is the impulse input to the
       system (not written as it is known).

       The version below takes advantage of the fact that a lot of the
       outputs are zero or known, for example if we put an inpulse
       into the first section the "clock" it 10 times only the first 3
       outputs samples are non-zero (it's an FIR filter).
    */

    ALLOC(xp, (m+1), spx_word32_t*);
    ALLOC(xpmem, (m+1)*(lpcrdr+1+2), spx_word32_t);

    ALLOC(xq, (m+1), spx_word32_t*);
    ALLOC(xqmem, (m+1)*(lpcrdr+1+2), spx_word32_t);
    
    for(i=0; i<=m; i++) {
      xp[i] = xpmem + i*(lpcrdr+1+2);
      xq[i] = xqmem + i*(lpcrdr+1+2);
    }

    /* work out 2cos terms in Q14 */

    ALLOC(freqn, lpcrdr, spx_word16_t);
    for (i=0;i<lpcrdr;i++) 
       freqn[i] = ANGLE2X(freq[i]);

    #define QIMP  21   /* scaling for impulse */

    xin = SHL32(EXTEND32(1), (QIMP-1)); /* 0.5 in QIMP format */
   
    /* first col and last non-zero values of each row are trivial */
    
    for(i=0;i<=m;i++) {
     xp[i][1] = 0;
     xp[i][2] = xin;
     xp[i][2+2*i] = xin;
     xq[i][1] = 0;
     xq[i][2] = xin;
     xq[i][2+2*i] = xin;
    }

    /* 2nd row (first output row) is trivial */

    xp[1][3] = -MULT16_32_Q14(freqn[0],xp[0][2]);
    xq[1][3] = -MULT16_32_Q14(freqn[1],xq[0][2]);

    xout1 = xout2 = 0;

    /* now generate remaining rows */

    for(i=1;i<m;i++) {

      for(j=1;j<2*(i+1)-1;j++) {
	mult = MULT16_32_Q14(freqn[2*i],xp[i][j+1]);
	xp[i+1][j+2] = ADD32(SUB32(xp[i][j+2], mult), xp[i][j]);
	mult = MULT16_32_Q14(freqn[2*i+1],xq[i][j+1]);
	xq[i+1][j+2] = ADD32(SUB32(xq[i][j+2], mult), xq[i][j]);
      }

      /* for last col xp[i][j+2] = xq[i][j+2] = 0 */

      mult = MULT16_32_Q14(freqn[2*i],xp[i][j+1]);
      xp[i+1][j+2] = SUB32(xp[i][j], mult);
      mult = MULT16_32_Q14(freqn[2*i+1],xq[i][j+1]);
      xq[i+1][j+2] = SUB32(xq[i][j], mult);
    }

    /* process last row to extra a{k} */

    for(j=1;j<=lpcrdr;j++) {
      int shift = QIMP-13;

      /* final filter sections */
      a = PSHR32(xp[m][j+2] + xout1 + xq[m][j+2] - xout2, shift); 
      xout1 = xp[m][j+2];
      xout2 = xq[m][j+2];
      
      /* hard limit ak's to +/- 32767 */

      if (a < -32767) a = -32767;
      if (a > 32767) a = 32767;
      ak[j-1] = (short)a;
     
    }

}

#else

void lsp_to_lpc(spx_lsp_t *freq,spx_coef_t *ak,int lpcrdr, char *stack)
/*  float *freq 	array of LSP frequencies in the x domain	*/
/*  float *ak 		array of LPC coefficients 			*/
/*  int lpcrdr  	order of LPC coefficients 			*/


{
    int i,j;
    float xout1,xout2,xin1,xin2;
    VARDECL(float *Wp);
    float *pw,*n1,*n2,*n3,*n4=NULL;
    VARDECL(float *x_freq);
    int m = lpcrdr>>1;

    ALLOC(Wp, 4*m+2, float);
    pw = Wp;

    /* initialise contents of array */

    for(i=0;i<=4*m+1;i++){       	/* set contents of buffer to 0 */
	*pw++ = 0.0;
    }

    /* Set pointers up */

    pw = Wp;
    xin1 = 1.0;
    xin2 = 1.0;

    ALLOC(x_freq, lpcrdr, float);
    for (i=0;i<lpcrdr;i++)
       x_freq[i] = ANGLE2X(freq[i]);

    /* reconstruct P(z) and Q(z) by  cascading second order
      polynomials in form 1 - 2xz(-1) +z(-2), where x is the
      LSP coefficient */

    for(j=0;j<=lpcrdr;j++){
       int i2=0;
	for(i=0;i<m;i++,i2+=2){
	    n1 = pw+(i*4);
	    n2 = n1 + 1;
	    n3 = n2 + 1;
	    n4 = n3 + 1;
	    xout1 = xin1 - 2.f*x_freq[i2] * *n1 + *n2;
	    xout2 = xin2 - 2.f*x_freq[i2+1] * *n3 + *n4;
	    *n2 = *n1;
	    *n4 = *n3;
	    *n1 = xin1;
	    *n3 = xin2;
	    xin1 = xout1;
	    xin2 = xout2;
	}
	xout1 = xin1 + *(n4+1);
	xout2 = xin2 - *(n4+2);
	if (j>0)
	   ak[j-1] = (xout1 + xout2)*0.5f;
	*(n4+1) = xin1;
	*(n4+2) = xin2;

	xin1 = 0.0;
	xin2 = 0.0;
    }

}
#endif


#ifdef FIXED_POINT

/*Makes sure the LSPs are stable*/
void lsp_enforce_margin(spx_lsp_t *lsp, int len, spx_word16_t margin)
{
   int i;
   spx_word16_t m = margin;
   spx_word16_t m2 = 25736-margin;
  
   if (lsp[0]<m)
      lsp[0]=m;
   if (lsp[len-1]>m2)
      lsp[len-1]=m2;
   for (i=1;i<len-1;i++)
   {
      if (lsp[i]<lsp[i-1]+m)
         lsp[i]=lsp[i-1]+m;

      if (lsp[i]>lsp[i+1]-m)
         lsp[i]= SHR16(lsp[i],1) + SHR16(lsp[i+1]-m,1);
   }
}


void lsp_interpolate(spx_lsp_t *old_lsp, spx_lsp_t *new_lsp, spx_lsp_t *interp_lsp, int len, int subframe, int nb_subframes)
{
   int i;
   spx_word16_t tmp = DIV32_16(SHL32(EXTEND32(1 + subframe),14),nb_subframes);
   spx_word16_t tmp2 = 16384-tmp;
   for (i=0;i<len;i++)
   {
      interp_lsp[i] = MULT16_16_P14(tmp2,old_lsp[i]) + MULT16_16_P14(tmp,new_lsp[i]);
   }
}

#else

/*Makes sure the LSPs are stable*/
void lsp_enforce_margin(spx_lsp_t *lsp, int len, spx_word16_t margin)
{
   int i;
   if (lsp[0]<LSP_SCALING*margin)
      lsp[0]=LSP_SCALING*margin;
   if (lsp[len-1]>LSP_SCALING*(M_PI-margin))
      lsp[len-1]=LSP_SCALING*(M_PI-margin);
   for (i=1;i<len-1;i++)
   {
      if (lsp[i]<lsp[i-1]+LSP_SCALING*margin)
         lsp[i]=lsp[i-1]+LSP_SCALING*margin;

      if (lsp[i]>lsp[i+1]-LSP_SCALING*margin)
         lsp[i]= .5f* (lsp[i] + lsp[i+1]-LSP_SCALING*margin);
   }
}


void lsp_interpolate(spx_lsp_t *old_lsp, spx_lsp_t *new_lsp, spx_lsp_t *interp_lsp, int len, int subframe, int nb_subframes)
{
   int i;
   float tmp = (1.0f + subframe)/nb_subframes;
   for (i=0;i<len;i++)
   {
      interp_lsp[i] = (1-tmp)*old_lsp[i] + tmp*new_lsp[i];
   }
}

#endif