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Implement the discrete sine/cosine transforms DCT-I and DST-I 

Originally committed as revision 22649 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Vitor Sessak 2010-03-23 19:48:16 +00:00
parent be548816dc
commit e1484ebed6
5 changed files with 93 additions and 16 deletions
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3
doc/APIchanges
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@ -12,6 +12,9 @@ libavutil: 2009-03-08
API changes, most recent first:
2010-03-15 - r22649 - lavc 52.59.0 - av_dct_init()
Support DCT-I and DST-I
2010-03-15 - r22540 - lavf 52.56.0 - AVFormatContext.start_time_realtime
Add AVFormatContext.start_time_realtime field.

2
libavcodec/avfft.c
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@ -116,7 +116,7 @@ void av_rdft_end(RDFTContext *s)
#if CONFIG_DCT
DCTContext *av_dct_init(int nbits, int inverse)
DCTContext *av_dct_init(int nbits, enum DCTTransformType inverse)
{
DCTContext *s = av_malloc(sizeof(*s));

18
libavcodec/avfft.h
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@ -77,12 +77,22 @@ void av_rdft_end(RDFTContext *s);
typedef struct DCTContext DCTContext;
enum DCTTransformType {
DCT_II = 0,
DCT_III,
DCT_I,
DST_I,
};
/**
* Set up (Inverse)DCT.
* @param nbits log2 of the length of the input array
* @param inverse >0 forward transform, <0 inverse transform
* Sets up DCT.
* @param nbits size of the input array:
* (1 << nbits) for DCT-II, DCT-III and DST-I
* (1 << nbits) + 1 for DCT-I
*
* @note the first element of the input of DST-I is ignored
*/
DCTContext *av_dct_init(int nbits, int inverse);
DCTContext *av_dct_init(int nbits, enum DCTTransformType type);
void av_dct_calc(DCTContext *s, FFTSample *data);
void av_dct_end (DCTContext *s);

75
libavcodec/dct.c
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@ -37,6 +37,66 @@
/* cos((M_PI * x / (2*n)) */
#define COS(s,n,x) (s->costab[x])
static void ff_dst_calc_I_c(DCTContext *ctx, FFTSample *data)
{
int n = 1 << ctx->nbits;
int i;
data[0] = 0;
for(i = 1; i < n/2; i++) {
float tmp1 = data[i ];
float tmp2 = data[n - i];
float s = SIN(ctx, n, 2*i);
s *= tmp1 + tmp2;
tmp1 = (tmp1 - tmp2) * 0.5f;
data[i ] = s + tmp1;
data[n - i] = s - tmp1;
}
data[n/2] *= 2;
ff_rdft_calc(&ctx->rdft, data);
data[0] *= 0.5f;
for(i = 1; i < n-2; i += 2) {
data[i + 1] += data[i - 1];
data[i ] = -data[i + 2];
}
data[n-1] = 0;
}
static void ff_dct_calc_I_c(DCTContext *ctx, FFTSample *data)
{
int n = 1 << ctx->nbits;
int i;
float next = -0.5f * (data[0] - data[n]);
for(i = 0; i < n/2; i++) {
float tmp1 = data[i ];
float tmp2 = data[n - i];
float s = SIN(ctx, n, 2*i);
float c = COS(ctx, n, 2*i);
c *= tmp1 - tmp2;
s *= tmp1 - tmp2;
next += c;
tmp1 = (tmp1 + tmp2) * 0.5f;
data[i ] = tmp1 - s;
data[n - i] = tmp1 + s;
}
ff_rdft_calc(&ctx->rdft, data);
data[n] = data[1];
data[1] = next;
for(i = 3; i <= n; i += 2)
data[i] = data[i - 2] - data[i];
}
static void ff_dct_calc_III_c(DCTContext *ctx, FFTSample *data)
{
int n = 1 << ctx->nbits;
@ -112,7 +172,7 @@ void ff_dct_calc(DCTContext *s, FFTSample *data)
s->dct_calc(s, data);
}
av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
av_cold int ff_dct_init(DCTContext *s, int nbits, enum DCTTransformType inverse)
{
int n = 1 << nbits;
int i;
@ -126,7 +186,7 @@ av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
s->csc2 = av_malloc(n/2 * sizeof(FFTSample));
if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {
if (ff_rdft_init(&s->rdft, nbits, inverse == DCT_III) < 0) {
av_free(s->csc2);
return -1;
}
@ -134,11 +194,12 @@ av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
for (i = 0; i < n/2; i++)
s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));
if(inverse) {
s->dct_calc = ff_dct_calc_III_c;
} else
s->dct_calc = ff_dct_calc_II_c;
switch(inverse) {
case DCT_I : s->dct_calc = ff_dct_calc_I_c; break;
case DCT_II : s->dct_calc = ff_dct_calc_II_c ; break;
case DCT_III: s->dct_calc = ff_dct_calc_III_c; break;
case DST_I : s->dct_calc = ff_dst_calc_I_c; break;
}
return 0;
}

11
libavcodec/fft.h
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@ -226,11 +226,14 @@ struct DCTContext {
};
/**
* Sets up (Inverse)DCT.
* @param nbits log2 of the length of the input array
* @param inverse >0 forward transform, <0 inverse transform
* Sets up DCT.
* @param nbits size of the input array:
* (1 << nbits) for DCT-II, DCT-III and DST-I
* (1 << nbits) + 1 for DCT-I
*
* @note the first element of the input of DST-I is ignored
*/
int ff_dct_init(DCTContext *s, int nbits, int inverse);
int ff_dct_init(DCTContext *s, int nbits, enum DCTTransformType type);
void ff_dct_calc(DCTContext *s, FFTSample *data);
void ff_dct_end (DCTContext *s);