1 /********************************************************************
3 * THIS FILE IS PART OF THE Ogg Vorbis SOFTWARE CODEC SOURCE CODE. *
4 * USE, DISTRIBUTION AND REPRODUCTION OF THIS SOURCE IS GOVERNED BY *
5 * THE GNU PUBLIC LICENSE 2, WHICH IS INCLUDED WITH THIS SOURCE. *
6 * PLEASE READ THESE TERMS DISTRIBUTING. *
8 * THE OggSQUISH SOURCE CODE IS (C) COPYRIGHT 1994-1999 *
9 * by 1999 Monty <monty@xiph.org> and The XIPHOPHORUS Company *
10 * http://www.xiph.org/ *
12 ********************************************************************
14 function: modified discrete cosine transform
15 power of two length transform only [16 <= n ]
17 author: Monty <xiphmont@mit.edu>
18 modifications by: Monty
19 last modification date: Oct 10 1999
21 Algorithm adapted from _The use of multirate filter banks for coding
22 of high quality digital audio_, by T. Sporer, K. Brandenburg and
23 B. Edler, collection of the European Signal Processing Conference
24 (EUSIPCO), Amsterdam, June 1992, Vol.1, pp 211-214
26 Note that the below code won't make much sense without the paper;
27 The presented algorithm was already fairly polished, and the code
28 once followed it closely. The current code both corrects several
29 typos in the paper and goes beyond the presented optimizations
30 (steps 4 through 6 are, for example, entirely eliminated).
32 This module DOES NOT INCLUDE code to generate the window function.
33 Everybody has their own weird favorite including me... I happen to
34 like the properties of y=sin(2PI*sin^2(x)), but others may vehemently
37 ********************************************************************/
45 /* build lookups for trig functions; also pre-figure scaling and
46 some window function algebra. */
48 void mdct_init(mdct_lookup *lookup,int n){
49 int *bitrev=malloc(sizeof(int)*(n/4));
50 double *trig=malloc(sizeof(double)*(n+n/4));
59 int log2n=lookup->log2n=rint(log(n)/log(2));
62 lookup->bitrev=bitrev;
67 AE[i*2]=cos((M_PI/n)*(4*i));
68 AO[i*2]=-sin((M_PI/n)*(4*i));
69 BE[i*2]=cos((M_PI/(2*n))*(2*i+1));
70 BO[i*2]=sin((M_PI/(2*n))*(2*i+1));
73 CE[i*2]=cos((M_PI/n)*(4*i+2));
74 CO[i*2]=-sin((M_PI/n)*(4*i+2));
77 /* bitreverse lookup... */
80 int mask=(1<<(log2n-1))-1,i,j;
85 if((msb>>j)&i)acc|=1<<j;
86 bitrev[i*2]=((~acc)&mask);
92 void mdct_clear(mdct_lookup *l){
94 if(l->trig)free(l->trig);
95 if(l->bitrev)free(l->bitrev);
96 memset(l,0,sizeof(mdct_lookup));
100 static inline double *_mdct_kernel(double *x, double *w,
101 int n, int n2, int n4, int n8,
110 double *A=init->trig+n2;
115 w2[i]= *xA++ + *xB++;
121 w[i++]= x0 * A[0] + x1 * A[1];
122 w[i]= x1 * A[0] - x0 * A[1];
124 w2[i++]= *xA++ + *xB++;
133 for(i=0;i<init->log2n-3;i++){
137 double *A=init->trig;
140 for(r=0;r<(k0>>2);r++){
148 for(s=0;s<(2<<i);s++){
152 wA =w[++w1] -w[++w2];
155 x[w2] =wA*AEv - wB*AOv;
156 x[w2-1]=wB*AEv + wA*AOv;
172 /* step 4, 5, 6, 7 */
174 double *C=init->trig+n;
175 int *bit=init->bitrev;
182 double wA=w[t1]-w[t2+1];
183 double wB=w[t1-1]+w[t2];
184 double wC=w[t1]+w[t2+1];
185 double wD=w[t1-1]-w[t2];
188 double wBCE=wB* *C++;
190 double wBCO=wB* *C++;
192 *x1++=( wC+wACO+wBCE)*.5;
193 *x2--=(-wD+wBCO-wACE)*.5;
194 *x1++=( wD+wBCO-wACE)*.5;
195 *x2--=( wC-wACO-wBCE)*.5;
201 void mdct_forward(mdct_lookup *init, double *in, double *out, double *window){
211 /* window + rotate + step 1 */
216 double *A=init->trig+n2;
222 tempA= in[in1+2]*window[in1+2] + in[in2]*window[in2];
223 tempB= in[in1]*window[in1] + in[in2+2]*window[in2+2];
225 x[i]= tempB*A[1] + tempA*A[0];
226 x[i+1]= tempB*A[0] - tempA*A[1];
233 tempA= in[in1+2]*window[in1+2] - in[in2]*window[in2];
234 tempB= in[in1]*window[in1] - in[in2+2]*window[in2+2];
236 x[i]= tempB*A[1] + tempA*A[0];
237 x[i+1]= tempB*A[0] - tempA*A[1];
244 tempA= -in[in1+2]*window[in1+2] - in[in2]*window[in2];
245 tempB= -in[in1]*window[in1] - in[in2+2]*window[in2+2];
247 x[i]= tempB*A[1] + tempA*A[0];
248 x[i+1]= tempB*A[0] - tempA*A[1];
252 xx=_mdct_kernel(x,w,n,n2,n4,n8,init);
257 double *B=init->trig+n2;
261 out[i] =(xx[0]*B[0]+xx[1]*B[1])*scale;
262 *(--out2)=(xx[0]*B[1]-xx[1]*B[0])*scale;
270 void mdct_backward(mdct_lookup *init, double *in, double *out, double *window){
280 /* window + rotate + step 1 */
284 double *A=init->trig+n2;
288 *xO++=-*(inO+2)*A[1] - *inO*A[0];
289 *xO++= *inO*A[1] - *(inO+2)*A[0];
297 *xO++=*inO*A[1] + *(inO+2)*A[0];
298 *xO++=*inO*A[0] - *(inO+2)*A[1];
304 xx=_mdct_kernel(x,w,n,n2,n4,n8,init);
309 double *B=init->trig+n2;
311 int o3=n4+n2,o4=o3-1;
314 double temp1= (*xx * B[1] - *(xx+1) * B[0]);
315 double temp2=-(*xx * B[0] + *(xx+1) * B[1]);
317 out[o1]=-temp1*window[o1];
318 out[o2]= temp1*window[o2];
319 out[o3]= temp2*window[o3];
320 out[o4]= temp2*window[o4];