ref: c093829c17dac65ff7bd4d595bc66d6070ff9a45
parent: aa3a599caa2aa2e4f3036eb0e3b848bf3946821e
author: Nils Wallménius <[email protected]>
date: Sun Dec 2 11:06:27 EST 2012
Do imdct post-rotate and deshuffle in-place. Gets rid of one stack buffer. Signed-off-by: Jean-Marc Valin <[email protected]>
--- a/celt/mdct.c
+++ b/celt/mdct.c
@@ -214,7 +214,6 @@
int i;
int N, N2, N4;
kiss_twiddle_scalar sine;
- VARDECL(kiss_fft_scalar, f);
VARDECL(kiss_fft_scalar, f2);
SAVE_STACK;
N = l->n;
@@ -221,7 +220,6 @@
N >>= shift;
N2 = N>>1;
N4 = N>>2;
- ALLOC(f, N2, kiss_fft_scalar);
ALLOC(f2, N2, kiss_fft_scalar);
/* sin(x) ~= x here */
#ifdef FIXED_POINT
@@ -251,26 +249,41 @@
}
/* Inverse N/4 complex FFT. This one should *not* downscale even in fixed-point */
- opus_ifft(l->kfft[shift], (kiss_fft_cpx *)f2, (kiss_fft_cpx *)f);
+ opus_ifft(l->kfft[shift], (kiss_fft_cpx *)f2, (kiss_fft_cpx *)(out+(overlap>>1)));
- /* Post-rotate and de-shuffle */
+ /* Post-rotate and de-shuffle from both ends of the buffer at once to make
+ it in-place. */
{- kiss_fft_scalar * OPUS_RESTRICT fp = f;
- kiss_fft_scalar * OPUS_RESTRICT yp0 = out+overlap/2;
- kiss_fft_scalar * OPUS_RESTRICT yp1 = out+overlap/2+N2-1;
+ kiss_fft_scalar * OPUS_RESTRICT yp0 = out+(overlap>>1);
+ kiss_fft_scalar * OPUS_RESTRICT yp1 = out+(overlap>>1)+N2-2;
const kiss_twiddle_scalar *t = &l->trig[0];
-
- for(i=0;i<N4;i++)
+ /* Loop to (N4+1)>>1 to handle odd N4. When N4 is odd, the
+ middle pair will be computed twice. */
+ for(i=0;i<(N4+1)>>1;i++)
{kiss_fft_scalar re, im, yr, yi;
- re = *fp++;
- im = *fp++;
+ kiss_twiddle_scalar t0, t1;
+ re = yp0[0];
+ im = yp0[1];
+ t0 = t[i<<shift];
+ t1 = t[(N4-i)<<shift];
/* We'd scale up by 2 here, but instead it's done when mixing the windows */
- yr = S_MUL(re,t[i<<shift]) - S_MUL(im,t[(N4-i)<<shift]);
- yi = S_MUL(im,t[i<<shift]) + S_MUL(re,t[(N4-i)<<shift]);
+ yr = S_MUL(re,t0) - S_MUL(im,t1);
+ yi = S_MUL(im,t0) + S_MUL(re,t1);
+ re = yp1[0];
+ im = yp1[1];
/* works because the cos is nearly one */
- *yp0 = -(yr - S_MUL(yi,sine));
- *yp1 = yi + S_MUL(yr,sine);
+ yp0[0] = -(yr - S_MUL(yi,sine));
+ yp1[1] = yi + S_MUL(yr,sine);
+
+ t0 = t[(N4-i-1)<<shift];
+ t1 = t[(i+1)<<shift];
+ /* We'd scale up by 2 here, but instead it's done when mixing the windows */
+ yr = S_MUL(re,t0) - S_MUL(im,t1);
+ yi = S_MUL(im,t0) + S_MUL(re,t1);
+ /* works because the cos is nearly one */
+ yp1[0] = -(yr - S_MUL(yi,sine));
+ yp0[1] = yi + S_MUL(yr,sine);
yp0 += 2;
yp1 -= 2;
}