/*====================================================================*/
void
sbt ( float vbuf[], float samp[] )
{
int i;
vbuf += 1152;
for ( i = 0; i < 36; i++ )
{
vbuf -= 32;
window ( vbuf );
fidct ( samp );
samp += 64; /* interleaved output */
}
/*-- done --*/
}
void flot2(float *x, float *y, int logm)
{
static int n, m, m2, m4;
static float tmp, fac, *xp1, *xp2, *yp1, *yp2;
/* Check range of logm */
if ((logm < 2) || (logm >MAXLOGM)) {
printf("Error : FLOT : logm = %d is out of bounds [%d, %d]\n",
logm, 2, MAXLOGM);
error_exit();
}
/* Define m */
m = 1 << logm;
m2 = m / 2;
m4 = m2 / 2;
/* Compute DCT */
fdct(x, logm);
/* Copy even-indexed x's on y[0] and
odd-indexed x's on y[m/2] */
xp1 = x;
yp1 = y;
yp2 = y + m2;
for (n = 0; n < m2; n++) {
*(yp1++) = *(xp1++);
*(yp2++) = *(xp1++);
}
/* First butterflies with +1/-1 factors, with 1/2 factor,
output in x */
xp1 = x;
xp2 = x + m2;
yp1 = y;
yp2 = y + m2;
for (n = 0; n < m2; n++ ) {
*(xp1++) = 0.5 * ( *yp1 + *yp2 );
*(xp2++) = 0.5 * ( *(yp1++) - *(yp2++) );
}
/* This piece of code correspond to the z^-1 delays in Section 4.4.
The stored values are in the last m/2 samples of y */
memcpy(y, y + m, m2 * sizeof(float));
memcpy(y + m, x + m2, m2 * sizeof(float));
/* Copy first m/2 coefficients of y in x[m/2] */
memcpy(x + m2, y, m2 * sizeof(float));
/* Second stage of +1/-1 butterflies, output in y */
xp1 = x;
xp2 = x + m2;
yp1 = y;
yp2 = y + m2;
for (n = 0; n < m2; n++) {
*(yp1++) = *xp1 + *xp2;
*(yp2++) = *xp1 - *xp2;
xp1++; xp2++;
}
/* Length-(n/2) IDCT */
fidct(y + m2, logm-1);
/* Length-(n/2) DST-IV via DCT-IV */
yp1 = y + m2 + 1;
for (n = 0; n < m4; n++) {
*yp1 = - *yp1;
yp1++; yp1++;
}
fdctiv(y + m2, logm-1);
yp1 = y + m2; yp2 = y + m - 1;
fac = sqrt(m2);
for (n = 0; n < m4; n++) {
tmp = *yp2;
*yp2 = fac * *yp1;
*yp1 = fac * tmp;
yp1++; yp2--;
}
/* Even/odd re-indexing, output in x */
xp1 = x;
yp1 = y;
yp2 = y + m2;
for (n = 0; n < m2; n++) {
*(xp1++) = *(yp1++);
*(xp1++) = *(yp2++);
}
}
