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lavu/tx: refactor power-of-two FFT

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This commit refactors the power-of-two FFT, making it faster and
halving the size of all tables, making the code much smaller on
all systems.
This removes the big/small pass split, because on modern systems
the "big" pass is always faster, and even on older machines there
is no measurable speed difference.
pull/362/head
Lynne 4 years ago
parent aa910a7ecd
commit 89da62f2fc
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GPG Key ID: A2FEA5F03F034464
2 changed files with 79 additions and 87 deletions
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  1. 2
      libavutil/tx_priv.h
  2. 164
      libavutil/tx_template.c

2
libavutil/tx_priv.h
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@ -105,7 +105,7 @@ typedef void FFTComplex;
CMUL((c).re, (c).im, (a).re, (a).im, (b).re, (b).im)
#define COSTABLE(size) \
DECLARE_ALIGNED(32, FFTSample, TX_NAME(ff_cos_##size))[size/2]
DECLARE_ALIGNED(32, FFTSample, TX_NAME(ff_cos_##size))[size/4 + 1]
/* Used by asm, reorder with care */
struct AVTXContext {

164
libavutil/tx_template.c
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@ -1,6 +1,8 @@
/*
* Copyright (c) 2019 Lynne <dev@lynne.ee>
* Copyright (c) Lynne
*
* Power of two FFT:
* Copyright (c) Lynne
* Copyright (c) 2008 Loren Merritt
* Copyright (c) 2002 Fabrice Bellard
* Partly based on libdjbfft by D. J. Bernstein
@ -65,10 +67,11 @@ static av_always_inline void init_cos_tabs_idx(int index)
int m = 1 << index;
double freq = 2*M_PI/m;
FFTSample *tab = cos_tabs[index];
for(int i = 0; i <= m/4; i++)
tab[i] = RESCALE(cos(i*freq));
for(int i = 1; i < m/4; i++)
tab[m/2 - i] = tab[i];
for (int i = 0; i < m/4; i++)
*tab++ = RESCALE(cos(i*freq));
*tab = 0;
}
#define INIT_FF_COS_TABS_FUNC(index, size) \
@ -214,76 +217,60 @@ static av_always_inline void fft15(FFTComplex *out, FFTComplex *in,
fft5_m3(out, tmp + 10, stride);
}
#define BUTTERFLIES(a0,a1,a2,a3) {\
BF(t3, t5, t5, t1);\
BF(a2.re, a0.re, a0.re, t5);\
BF(a3.im, a1.im, a1.im, t3);\
BF(t4, t6, t2, t6);\
BF(a3.re, a1.re, a1.re, t4);\
BF(a2.im, a0.im, a0.im, t6);\
}
// force loading all the inputs before storing any.
// this is slightly slower for small data, but avoids store->load aliasing
// for addresses separated by large powers of 2.
#define BUTTERFLIES_BIG(a0,a1,a2,a3) {\
FFTSample r0=a0.re, i0=a0.im, r1=a1.re, i1=a1.im;\
BF(t3, t5, t5, t1);\
BF(a2.re, a0.re, r0, t5);\
BF(a3.im, a1.im, i1, t3);\
BF(t4, t6, t2, t6);\
BF(a3.re, a1.re, r1, t4);\
BF(a2.im, a0.im, i0, t6);\
}
#define TRANSFORM(a0,a1,a2,a3,wre,wim) {\
CMUL(t1, t2, a2.re, a2.im, wre, -wim);\
CMUL(t5, t6, a3.re, a3.im, wre, wim);\
BUTTERFLIES(a0,a1,a2,a3)\
}
#define TRANSFORM_ZERO(a0,a1,a2,a3) {\
t1 = a2.re;\
t2 = a2.im;\
t5 = a3.re;\
t6 = a3.im;\
BUTTERFLIES(a0,a1,a2,a3)\
}
#define BUTTERFLIES(a0,a1,a2,a3) \
do { \
r0=a0.re; \
i0=a0.im; \
r1=a1.re; \
i1=a1.im; \
BF(t3, t5, t5, t1); \
BF(a2.re, a0.re, r0, t5); \
BF(a3.im, a1.im, i1, t3); \
BF(t4, t6, t2, t6); \
BF(a3.re, a1.re, r1, t4); \
BF(a2.im, a0.im, i0, t6); \
} while (0)
#define TRANSFORM(a0,a1,a2,a3,wre,wim) \
do { \
CMUL(t1, t2, a2.re, a2.im, wre, -wim); \
CMUL(t5, t6, a3.re, a3.im, wre, wim); \
BUTTERFLIES(a0, a1, a2, a3); \
} while (0)
/* z[0...8n-1], w[1...2n-1] */
#define PASS(name)\
static void name(FFTComplex *z, const FFTSample *wre, unsigned int n)\
{\
FFTSample t1, t2, t3, t4, t5, t6;\
int o1 = 2*n;\
int o2 = 4*n;\
int o3 = 6*n;\
const FFTSample *wim = wre+o1;\
n--;\
\
TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3]);\
TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
do {\
z += 2;\
wre += 2;\
wim -= 2;\
TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0]);\
TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
} while(--n);\
static void split_radix_combine(FFTComplex *z, const FFTSample *cos, int n)
{
int o1 = 2*n;
int o2 = 4*n;
int o3 = 6*n;
const FFTSample *wim = cos + o1 - 7;
FFTSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
for (int i = 0; i < n; i += 4) {
TRANSFORM(z[0], z[o1 + 0], z[o2 + 0], z[o3 + 0], cos[0], wim[7]);
TRANSFORM(z[2], z[o1 + 2], z[o2 + 2], z[o3 + 2], cos[2], wim[5]);
TRANSFORM(z[4], z[o1 + 4], z[o2 + 4], z[o3 + 4], cos[4], wim[3]);
TRANSFORM(z[6], z[o1 + 6], z[o2 + 6], z[o3 + 6], cos[6], wim[1]);
TRANSFORM(z[1], z[o1 + 1], z[o2 + 1], z[o3 + 1], cos[1], wim[6]);
TRANSFORM(z[3], z[o1 + 3], z[o2 + 3], z[o3 + 3], cos[3], wim[4]);
TRANSFORM(z[5], z[o1 + 5], z[o2 + 5], z[o3 + 5], cos[5], wim[2]);
TRANSFORM(z[7], z[o1 + 7], z[o2 + 7], z[o3 + 7], cos[7], wim[0]);
z += 2*4;
cos += 2*4;
wim -= 2*4;
}
}
PASS(pass)
#undef BUTTERFLIES
#define BUTTERFLIES BUTTERFLIES_BIG
PASS(pass_big)
#define DECL_FFT(n,n2,n4)\
static void fft##n(FFTComplex *z)\
{\
fft##n2(z);\
fft##n4(z+n4*2);\
fft##n4(z+n4*3);\
pass(z,TX_NAME(ff_cos_##n),n4/2);\
#define DECL_FFT(n, n2, n4) \
static void fft##n(FFTComplex *z) \
{ \
fft##n2(z); \
fft##n4(z + n4*2); \
fft##n4(z + n4*3); \
split_radix_combine(z, TX_NAME(ff_cos_##n), n4/2); \
}
static void fft2(FFTComplex *z)
@ -310,7 +297,7 @@ static void fft4(FFTComplex *z)
static void fft8(FFTComplex *z)
{
FFTSample t1, t2, t3, t4, t5, t6;
FFTSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
fft4(z);
@ -319,24 +306,30 @@ static void fft8(FFTComplex *z)
BF(t5, z[7].re, z[6].re, -z[7].re);
BF(t6, z[7].im, z[6].im, -z[7].im);
BUTTERFLIES(z[0],z[2],z[4],z[6]);
TRANSFORM(z[1],z[3],z[5],z[7],RESCALE(M_SQRT1_2),RESCALE(M_SQRT1_2));
BUTTERFLIES(z[0], z[2], z[4], z[6]);
TRANSFORM(z[1], z[3], z[5], z[7], RESCALE(M_SQRT1_2), RESCALE(M_SQRT1_2));
}
static void fft16(FFTComplex *z)
{
FFTSample t1, t2, t3, t4, t5, t6;
FFTSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
FFTSample cos_16_1 = TX_NAME(ff_cos_16)[1];
FFTSample cos_16_2 = TX_NAME(ff_cos_16)[2];
FFTSample cos_16_3 = TX_NAME(ff_cos_16)[3];
fft8(z);
fft4(z+8);
fft4(z+12);
fft8(z + 0);
fft4(z + 8);
fft4(z + 12);
t1 = z[ 8].re;
t2 = z[ 8].im;
t5 = z[12].re;
t6 = z[12].im;
BUTTERFLIES(z[0], z[4], z[8], z[12]);
TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
TRANSFORM(z[2],z[6],z[10],z[14],RESCALE(M_SQRT1_2),RESCALE(M_SQRT1_2));
TRANSFORM(z[1],z[5],z[9],z[13],cos_16_1,cos_16_3);
TRANSFORM(z[3],z[7],z[11],z[15],cos_16_3,cos_16_1);
TRANSFORM(z[ 2], z[ 6], z[10], z[14], cos_16_2, cos_16_2);
TRANSFORM(z[ 1], z[ 5], z[ 9], z[13], cos_16_1, cos_16_3);
TRANSFORM(z[ 3], z[ 7], z[11], z[15], cos_16_3, cos_16_1);
}
DECL_FFT(32,16,8)
@ -344,7 +337,6 @@ DECL_FFT(64,32,16)
DECL_FFT(128,64,32)
DECL_FFT(256,128,64)
DECL_FFT(512,256,128)
#define pass pass_big
DECL_FFT(1024,512,256)
DECL_FFT(2048,1024,512)
DECL_FFT(4096,2048,1024)
@ -386,8 +378,8 @@ DECL_COMP_FFT(3)
DECL_COMP_FFT(5)
DECL_COMP_FFT(15)
static void monolithic_fft(AVTXContext *s, void *_out, void *_in,
ptrdiff_t stride)
static void split_radix_fft(AVTXContext *s, void *_out, void *_in,
ptrdiff_t stride)
{
FFTComplex *in = _in;
FFTComplex *out = _out;
@ -730,7 +722,7 @@ int TX_NAME(ff_tx_init_mdct_fft)(AVTXContext *s, av_tx_fn *tx,
n == 5 ? inv ? compound_imdct_5xM : compound_mdct_5xM :
inv ? compound_imdct_15xM : compound_mdct_15xM;
} else { /* Direct transform case */
*tx = monolithic_fft;
*tx = split_radix_fft;
if (is_mdct)
*tx = inv ? monolithic_imdct : monolithic_mdct;
}

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