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lavu: support arbitrary-point FFTs and all even (i)MDCT transforms

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This patch adds support for arbitrary-point FFTs and all even MDCT
transforms.
Odd MDCTs are not supported yet as they're based on the DCT-II and DCT-III
and they're very niche.

With this we can now write tests.
This commit is contained in:
Lynne 2021-01-12 08:11:47 +01:00
parent ca21cb1e36
commit 06a8596825
No known key found for this signature in database
GPG Key ID: A2FEA5F03F034464
4 changed files with 102 additions and 9 deletions
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5
libavutil/tx.h
View File

@ -51,6 +51,8 @@ enum AVTXType {
* For inverse transforms, the stride specifies the spacing between each
* sample in the input array in bytes. The output will be a flat array.
* Stride must be a non-zero multiple of sizeof(float).
* NOTE: the inverse transform is half-length, meaning the output will not
* contain redundant data. This is what most codecs work with.
*/
AV_TX_FLOAT_MDCT = 1,
/**
@ -93,8 +95,7 @@ typedef void (*av_tx_fn)(AVTXContext *s, void *out, void *in, ptrdiff_t stride);
/**
* Initialize a transform context with the given configuration
* Currently power of two lengths from 2 to 131072 are supported, along with
* any length decomposable to a power of two and either 3, 5 or 15.
* (i)MDCTs with an odd length are currently not supported.
*
* @param ctx the context to allocate, will be NULL on error
* @param tx pointer to the transform function pointer to set

3
libavutil/tx_priv.h
View File

@ -58,6 +58,7 @@ typedef void FFTComplex;
(dim) = (are) * (bim) - (aim) * (bre); \
} while (0)
#define UNSCALE(x) (x)
#define RESCALE(x) (x)
#define FOLD(a, b) ((a) + (b))
@ -85,6 +86,7 @@ typedef void FFTComplex;
(dim) = (int)(((accu) + 0x40000000) >> 31); \
} while (0)
#define UNSCALE(x) ((double)x/2147483648.0)
#define RESCALE(x) (av_clip64(lrintf((x) * 2147483648.0), INT32_MIN, INT32_MAX))
#define FOLD(x, y) ((int)((x) + (unsigned)(y) + 32) >> 6)
@ -108,6 +110,7 @@ struct AVTXContext {
int m; /* Ptwo part */
int inv; /* Is inverted */
int type; /* Type */
double scale; /* Scale */
FFTComplex *exptab; /* MDCT exptab */
FFTComplex *tmp; /* Temporary buffer needed for all compound transforms */

101
libavutil/tx_template.c
View File

@ -397,6 +397,31 @@ static void monolithic_fft(AVTXContext *s, void *_out, void *_in,
fft_dispatch[mb](out);
}
static void naive_fft(AVTXContext *s, void *_out, void *_in,
ptrdiff_t stride)
{
FFTComplex *in = _in;
FFTComplex *out = _out;
const int n = s->n;
double phase = s->inv ? 2.0*M_PI/n : -2.0*M_PI/n;
for(int i = 0; i < n; i++) {
FFTComplex tmp = { 0 };
for(int j = 0; j < n; j++) {
const double factor = phase*i*j;
const FFTComplex mult = {
RESCALE(cos(factor)),
RESCALE(sin(factor)),
};
FFTComplex res;
CMUL3(res, in[j], mult);
tmp.re += res.re;
tmp.im += res.im;
}
out[i] = tmp;
}
}
#define DECL_COMP_IMDCT(N) \
static void compound_imdct_##N##xM(AVTXContext *s, void *_dst, void *_src, \
ptrdiff_t stride) \
@ -553,6 +578,57 @@ static void monolithic_mdct(AVTXContext *s, void *_dst, void *_src,
}
}
static void naive_imdct(AVTXContext *s, void *_dst, void *_src,
ptrdiff_t stride)
{
int len = s->n;
int len2 = len*2;
FFTSample *src = _src;
FFTSample *dst = _dst;
double scale = s->scale;
const double phase = M_PI/(4.0*len2);
stride /= sizeof(*src);
for (int i = 0; i < len; i++) {
double sum_d = 0.0;
double sum_u = 0.0;
double i_d = phase * (4*len - 2*i - 1);
double i_u = phase * (3*len2 + 2*i + 1);
for (int j = 0; j < len2; j++) {
double a = (2 * j + 1);
double a_d = cos(a * i_d);
double a_u = cos(a * i_u);
double val = UNSCALE(src[j*stride]);
sum_d += a_d * val;
sum_u += a_u * val;
}
dst[i + 0] = RESCALE( sum_d*scale);
dst[i + len] = RESCALE(-sum_u*scale);
}
}
static void naive_mdct(AVTXContext *s, void *_dst, void *_src,
ptrdiff_t stride)
{
int len = s->n*2;
FFTSample *src = _src;
FFTSample *dst = _dst;
double scale = s->scale;
const double phase = M_PI/(4.0*len);
stride /= sizeof(*dst);
for (int i = 0; i < len; i++) {
double sum = 0.0;
for (int j = 0; j < len*2; j++) {
int a = (2*j + 1 + len) * (2*i + 1);
sum += UNSCALE(src[j]) * cos(a * phase);
}
dst[i*stride] = RESCALE(sum*scale);
}
}
static int gen_mdct_exptab(AVTXContext *s, int len4, double scale)
{
const double theta = (scale < 0 ? len4 : 0) + 1.0/8.0;
@ -575,11 +651,13 @@ int TX_NAME(ff_tx_init_mdct_fft)(AVTXContext *s, av_tx_fn *tx,
const void *scale, uint64_t flags)
{
const int is_mdct = ff_tx_type_is_mdct(type);
int err, n = 1, m = 1, max_ptwo = 1 << (FF_ARRAY_ELEMS(fft_dispatch) - 1);
int err, l, n = 1, m = 1, max_ptwo = 1 << (FF_ARRAY_ELEMS(fft_dispatch) - 1);
if (is_mdct)
len >>= 1;
l = len;
#define CHECK_FACTOR(DST, FACTOR, SRC) \
if (DST == 1 && !(SRC % FACTOR)) { \
DST = FACTOR; \
@ -601,12 +679,23 @@ int TX_NAME(ff_tx_init_mdct_fft)(AVTXContext *s, av_tx_fn *tx,
s->inv = inv;
s->type = type;
/* Filter out direct 3, 5 and 15 transforms, too niche */
/* If we weren't able to split the length into factors we can handle,
* resort to using the naive and slow FT. This also filters out
* direct 3, 5 and 15 transforms as they're too niche. */
if (len > 1 || m == 1) {
av_log(NULL, AV_LOG_ERROR, "Unsupported transform size: n = %i, "
"m = %i, residual = %i!\n", n, m, len);
return AVERROR(EINVAL);
} else if (n > 1 && m > 1) { /* 2D transform case */
if (is_mdct && (l & 1)) /* Odd (i)MDCTs are not supported yet */
return AVERROR(ENOTSUP);
s->n = l;
s->m = 1;
*tx = naive_fft;
if (is_mdct) {
s->scale = *((SCALE_TYPE *)scale);
*tx = inv ? naive_imdct : naive_mdct;
}
return 0;
}
if (n > 1 && m > 1) { /* 2D transform case */
if ((err = ff_tx_gen_compound_mapping(s)))
return err;
if (!(s->tmp = av_malloc(n*m*sizeof(*s->tmp))))

2
libavutil/version.h
View File

@ -80,7 +80,7 @@
#define LIBAVUTIL_VERSION_MAJOR 56
#define LIBAVUTIL_VERSION_MINOR 63
#define LIBAVUTIL_VERSION_MICRO 100
#define LIBAVUTIL_VERSION_MICRO 101
#define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
LIBAVUTIL_VERSION_MINOR, \