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opus: use two pointers for mdct pre and post rotation

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avoids complicated index calculations in the loops.
saves 0.3MHz decoding a 64kbps test file on h300 (cf) and
0.2MHz on c200 (pp)

Change-Id: I1918912d9a4502f89980c6bb270ec2ef10a07010
Signed-off-by: Nils Wallménius <nils@rockbox.org>
This commit is contained in:
Andree Buschmann 2012-10-16 18:06:16 +02:00 • committed by Nils Wallménius
parent c8e7dae362
commit 091619b4a5
1 changed files with 12 additions and 7 deletions
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19
lib/rbcodec/codecs/libopus/celt/mdct.c
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@ -249,17 +249,20 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala
const kiss_fft_scalar * OPUS_RESTRICT xp1 = in;
const kiss_fft_scalar * OPUS_RESTRICT xp2 = in+stride*(N2-1);
kiss_fft_scalar * OPUS_RESTRICT yp = f2;
const kiss_twiddle_scalar *t = &l->trig[0];
const kiss_twiddle_scalar *t0 = &l->trig[0];
const kiss_twiddle_scalar *t1 = &l->trig[N4<<shift];
for(i=0;i<N4;i++)
{
kiss_fft_scalar yr, yi;
yr = -S_MUL(*xp2, t[i<<shift]) + S_MUL(*xp1,t[(N4-i)<<shift]);
yi = -S_MUL(*xp2, t[(N4-i)<<shift]) - S_MUL(*xp1,t[i<<shift]);
yr = -S_MUL(*xp2, *t0) + S_MUL(*xp1, *t1);
yi = -S_MUL(*xp2, *t1) - S_MUL(*xp1, *t0);
/* works because the cos is nearly one */
*yp++ = yr - S_MUL(yi,sine);
*yp++ = yi + S_MUL(yr,sine);
xp1+=2*stride;
xp2-=2*stride;
t0 += stride;
t1 -= stride;
}
}
@ -269,19 +272,21 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala
/* Post-rotate */
{
kiss_fft_scalar * OPUS_RESTRICT fp = f;
const kiss_twiddle_scalar *t = &l->trig[0];
const kiss_twiddle_scalar *t0 = &l->trig[0];
const kiss_twiddle_scalar *t1 = &l->trig[N4<<shift];
for(i=0;i<N4;i++)
{
kiss_fft_scalar re, im, yr, yi;
re = fp[0];
im = fp[1];
/* 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);
/* works because the cos is nearly one */
*fp++ = yr - S_MUL(yi,sine);
*fp++ = yi + S_MUL(yr,sine);
t0 += stride;
t1 -= stride;
}
}
/* De-shuffle the components for the middle of the window only */