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));
62 int log2n=lookup->log2n=rint(log(n)/log(2));
65 lookup->bitrev=bitrev;
70 AE[i*2]=cos((M_PI/n)*(4*i));
71 AO[i*2]=-sin((M_PI/n)*(4*i));
72 BE[i*2]=cos((M_PI/(2*n))*(2*i+1));
73 BO[i*2]=sin((M_PI/(2*n))*(2*i+1));
76 CE[i*2]=cos((M_PI/n)*(4*i+2));
77 CO[i*2]=-sin((M_PI/n)*(4*i+2));
80 /* bitreverse lookup... */
83 int mask=(1<<(log2n-1))-1,i,j;
88 if((msb>>j)&i)acc|=1<<j;
89 bitA[i*2]=((~acc)&mask);
95 void mdct_clear(mdct_lookup *l){
97 if(l->trig)free(l->trig);
98 if(l->bitrev)free(l->bitrev);
99 memset(l,0,sizeof(mdct_lookup));
103 static inline double *_mdct_kernel(double *x, double *w,
104 int n, int n2, int n4, int n8,
113 double *A=init->trig+n2;
118 w2[i]= *xA++ + *xB++;
124 w[i++]= x0 * A[0] + x1 * A[1];
125 w[i]= x1 * A[0] - x0 * A[1];
127 w2[i++]= *xA++ + *xB++;
136 for(i=0;i<init->log2n-3;i++){
140 double *A=init->trig;
143 for(r=0;r<(k0>>2);r++){
151 for(s=0;s<(2<<i);s++){
155 wA =w[++w1] -w[++w2];
158 x[w2] =wA*AEv - wB*AOv;
159 x[w2-1]=wB*AEv + wA*AOv;
175 /* step 4, 5, 6, 7 */
177 double *C=init->trig+n;
178 int *bit=init->bitrev;
185 double wA=w[t1]-w[t2+1];
186 double wB=w[t1-1]+w[t2];
187 double wC=w[t1]+w[t2+1];
188 double wD=w[t1-1]-w[t2];
191 double wBCE=wB* *C++;
193 double wBCO=wB* *C++;
195 *x1++=( wC+wACO+wBCE)*.5;
196 *x2--=(-wD+wBCO-wACE)*.5;
197 *x1++=( wD+wBCO-wACE)*.5;
198 *x2--=( wC-wACO-wBCE)*.5;
204 void mdct_forward(mdct_lookup *init, double *in, double *out, double *window){
214 /* window + rotate + step 1 */
219 double *A=init->trig+n2;
225 tempA= in[in1+2]*window[in1+2] + in[in2]*window[in2];
226 tempB= in[in1]*window[in1] + in[in2+2]*window[in2+2];
228 x[i]= tempB*A[1] + tempA*A[0];
229 x[i+1]= tempB*A[0] - tempA*A[1];
236 tempA= in[in1+2]*window[in1+2] - in[in2]*window[in2];
237 tempB= in[in1]*window[in1] - in[in2+2]*window[in2+2];
239 x[i]= tempB*A[1] + tempA*A[0];
240 x[i+1]= tempB*A[0] - tempA*A[1];
247 tempA= -in[in1+2]*window[in1+2] - in[in2]*window[in2];
248 tempB= -in[in1]*window[in1] - in[in2+2]*window[in2+2];
250 x[i]= tempB*A[1] + tempA*A[0];
251 x[i+1]= tempB*A[0] - tempA*A[1];
255 xx=_mdct_kernel(x,w,n,n2,n4,n8,init);
260 double *B=init->trig+n2;
264 out[i] =(xx[0]*B[0]+xx[1]*B[1])*scale;
265 *(--out2)=(xx[0]*B[1]-xx[1]*B[0])*scale;
273 void mdct_backward(mdct_lookup *init, double *in, double *out, double *window){
283 /* window + rotate + step 1 */
287 double *A=init->trig+n2;
291 *xO++=-*(inO+2)*A[1] - *inO*A[0];
292 *xO++= *inO*A[1] - *(inO+2)*A[0];
300 *xO++=*inO*A[1] + *(inO+2)*A[0];
301 *xO++=*inO*A[0] - *(inO+2)*A[1];
307 xx=_mdct_kernel(x,w,n,n2,n4,n8,init);
312 double *B=init->trig+n2;
314 int o3=n4+n2,o4=o3-1;
317 double temp1= (*xx * B[1] - *(xx+1) * B[0]);
318 double temp2=-(*xx * B[0] + *(xx+1) * B[1]);
320 out[o1]=-temp1*window[o1];
321 out[o2]= temp1*window[o2];
322 out[o3]= temp2*window[o3];
323 out[o4]= temp2*window[o4];