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Shrinking the MDCT's table by separately rotating by the 1/(8N) factor

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This commit is contained in:
Jean-Marc Valin 2010-04-28 22:10:57 -04:00
parent 65ee67ac55
commit f7547a4e8e
1 changed files with 49 additions and 24 deletions

71
libcelt/mdct.c
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@ -61,29 +61,30 @@
void clt_mdct_init(mdct_lookup *l,int N) void clt_mdct_init(mdct_lookup *l,int N)
{ {
int i; int i;
int N2; int N2, N4;
l->n = N; l->n = N;
N2 = N>>1; N2 = N>>1;
N4 = N>>2;
l->kfft = cpx32_fft_alloc(N>>2); l->kfft = cpx32_fft_alloc(N>>2);
#ifndef ENABLE_TI_DSPLIB55 #ifndef ENABLE_TI_DSPLIB55
if (l->kfft==NULL) if (l->kfft==NULL)
return; return;
#endif #endif
l->trig = (kiss_twiddle_scalar*)celt_alloc(N2*sizeof(kiss_twiddle_scalar)); l->trig = (kiss_twiddle_scalar*)celt_alloc((N4+1)*sizeof(kiss_twiddle_scalar));
if (l->trig==NULL) if (l->trig==NULL)
return; return;
/* We have enough points that sine isn't necessary */ /* We have enough points that sine isn't necessary */
#if defined(FIXED_POINT) #if defined(FIXED_POINT)
#if defined(DOUBLE_PRECISION) & !defined(MIXED_PRECISION) #if defined(DOUBLE_PRECISION) & !defined(MIXED_PRECISION)
for (i=0;i<N2;i++) for (i=0;i<=N4;i++)
l->trig[i] = SAMP_MAX*cos(2*M_PI*(i+1./8.)/N); l->trig[i] = SAMP_MAX*cos(2*M_PI*i/N);
#else #else
for (i=0;i<N2;i++) for (i=0;i<=N4;i++)
l->trig[i] = TRIG_UPSCALE*celt_cos_norm(DIV32(ADD32(SHL32(EXTEND32(i),17),16386),N)); l->trig[i] = TRIG_UPSCALE*celt_cos_norm(DIV32(ADD32(SHL32(EXTEND32(i),17),N2),N));
#endif #endif
#else #else
for (i=0;i<N2;i++) for (i=0;i<=N4;i++)
l->trig[i] = cos(2*M_PI*(i+.125f)/N); l->trig[i] = cos(2*M_PI*i/N);
#endif #endif
} }
@ -102,9 +103,16 @@ void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar
N = l->n; N = l->n;
N2 = N>>1; N2 = N>>1;
N4 = N>>2; N4 = N>>2;
kiss_twiddle_scalar sine;
ALLOC(f, N2, kiss_fft_scalar); ALLOC(f, N2, kiss_fft_scalar);
/* sin(x) ~= x here */
#ifdef FIXED_POINT
sine = TRIG_UPSCALE*(QCONST16(0.7853981f, 15)+N2)/N;
#else
sine = 2*M_PI*(.125f)/N;
#endif
/* Consider the input to be compused of four blocks: [a, b, c, d] */ /* Consider the input to be composed of four blocks: [a, b, c, d] */
/* Window, shuffle, fold */ /* Window, shuffle, fold */
{ {
/* Temp pointers to make it really clear to the compiler what we're doing */ /* Temp pointers to make it really clear to the compiler what we're doing */
@ -150,12 +158,14 @@ void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar
kiss_fft_scalar *t = &l->trig[0]; kiss_fft_scalar *t = &l->trig[0];
for(i=0;i<N4;i++) for(i=0;i<N4;i++)
{ {
kiss_fft_scalar re, im; kiss_fft_scalar re, im, yr, yi;
re = yp[0]; re = yp[0];
im = yp[1]; im = yp[1];
*yp++ = -S_MUL(re,t[0]) + S_MUL(im,t[N4]); yr = -S_MUL(re,t[i]) - S_MUL(im,t[N4-i]);
*yp++ = -S_MUL(im,t[0]) - S_MUL(re,t[N4]); yi = -S_MUL(im,t[i]) + S_MUL(re,t[N4-i]);
t++; /* works because the cos is nearly one */
*yp++ = yr + S_MUL(yi,sine);
*yp++ = yi - S_MUL(yr,sine);
} }
} }
@ -172,12 +182,15 @@ void clt_mdct_forward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scalar
/* Temp pointers to make it really clear to the compiler what we're doing */ /* Temp pointers to make it really clear to the compiler what we're doing */
for(i=0;i<N4;i++) for(i=0;i<N4;i++)
{ {
*yp1 = -S_MUL(fp[1],t[N4]) + S_MUL(fp[0],t[0]); kiss_fft_scalar yr, yi;
*yp2 = -S_MUL(fp[0],t[N4]) - S_MUL(fp[1],t[0]); yr = S_MUL(fp[1],t[N4-i]) + S_MUL(fp[0],t[i]);
yi = S_MUL(fp[0],t[N4-i]) - S_MUL(fp[1],t[i]);
/* works because the cos is nearly one */
*yp1 = yr - S_MUL(yi,sine);
*yp2 = yi + S_MUL(yr,sine);;
fp += 2; fp += 2;
yp1 += 2; yp1 += 2;
yp2 -= 2; yp2 -= 2;
t++;
} }
} }
RESTORE_STACK; RESTORE_STACK;
@ -194,8 +207,15 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala
N = l->n; N = l->n;
N2 = N>>1; N2 = N>>1;
N4 = N>>2; N4 = N>>2;
kiss_twiddle_scalar sine;
ALLOC(f, N2, kiss_fft_scalar); ALLOC(f, N2, kiss_fft_scalar);
ALLOC(f2, N2, kiss_fft_scalar); ALLOC(f2, N2, kiss_fft_scalar);
/* sin(x) ~= x here */
#ifdef FIXED_POINT
sine = TRIG_UPSCALE*(QCONST16(0.7853981f, 15)+N2)/N;
#else
sine = 2*M_PI*(.125f)/N;
#endif
/* Pre-rotate */ /* Pre-rotate */
{ {
@ -206,11 +226,14 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala
kiss_fft_scalar *t = &l->trig[0]; kiss_fft_scalar *t = &l->trig[0];
for(i=0;i<N4;i++) for(i=0;i<N4;i++)
{ {
*yp++ = -S_MUL(*xp2, t[0]) - S_MUL(*xp1,t[N4]); kiss_fft_scalar yr, yi;
*yp++ = S_MUL(*xp2, t[N4]) - S_MUL(*xp1,t[0]); yr = -S_MUL(*xp2, t[i]) + S_MUL(*xp1,t[N4-i]);
yi = -S_MUL(*xp2, t[N4-i]) - S_MUL(*xp1,t[i]);
/* works because the cos is nearly one */
*yp++ = yr - S_MUL(yi,sine);
*yp++ = yi + S_MUL(yr,sine);
xp1+=2; xp1+=2;
xp2-=2; xp2-=2;
t++;
} }
} }
@ -224,13 +247,15 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala
for(i=0;i<N4;i++) for(i=0;i<N4;i++)
{ {
kiss_fft_scalar re, im; kiss_fft_scalar re, im, yr, yi;
re = fp[0]; re = fp[0];
im = fp[1]; im = fp[1];
/* We'd scale up by 2 here, but instead it's done when mixing the windows */ /* We'd scale up by 2 here, but instead it's done when mixing the windows */
*fp++ = S_MUL(re,*t) + S_MUL(im,t[N4]); yr = S_MUL(re,t[i]) - S_MUL(im,t[N4-i]);
*fp++ = S_MUL(im,*t) - S_MUL(re,t[N4]); yi = S_MUL(im,t[i]) + S_MUL(re,t[N4-i]);
t++; /* works because the cos is nearly one */
*fp++ = yr - S_MUL(yi,sine);
*fp++ = yi + S_MUL(yr,sine);
} }
} }
/* De-shuffle the components for the middle of the window only */ /* De-shuffle the components for the middle of the window only */