[FFmpeg-devel] [PATCH] avcodec/rdft: remove sintable

[Muhammad Faiz]

On Wed, Jul 5, 2017 at 10:22 PM, Rostislav Pehlivanov
<atomnuker at gmail.com> wrote:
> On 5 July 2017 at 11:33, Muhammad Faiz <mfcc64 at gmail.com> wrote:
>
>> It is redundant with costable. The first half of sintable is
>> identical with the second half of costable. The second half
>> of sintable is negative value of the first half of sintable.
>>
>> The computation is changed to handle sign of sin values,
>> so disable arm optimization.
>>
>> Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
>> ---
>>  libavcodec/Makefile |  3 +--
>>  libavcodec/rdft.c   | 70 +++++++++++++++++++-----------
>> -----------------------
>>  libavcodec/rdft.h   | 25 +------------------
>>  3 files changed, 27 insertions(+), 71 deletions(-)
>>
>> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
>> index b440a00..59029a8 100644
>> --- a/libavcodec/Makefile
>> +++ b/libavcodec/Makefile
>> @@ -122,8 +122,7 @@ OBJS-$(CONFIG_QSV)                     += qsv.o
>>  OBJS-$(CONFIG_QSVDEC)                  += qsvdec.o
>>  OBJS-$(CONFIG_QSVENC)                  += qsvenc.o
>>  OBJS-$(CONFIG_RANGECODER)              += rangecoder.o
>> -RDFT-OBJS-$(CONFIG_HARDCODED_TABLES)   += sin_tables.o
>> -OBJS-$(CONFIG_RDFT)                    += rdft.o $(RDFT-OBJS-yes)
>> +OBJS-$(CONFIG_RDFT)                    += rdft.o
>>  OBJS-$(CONFIG_RV34DSP)                 += rv34dsp.o
>>  OBJS-$(CONFIG_SHARED)                  += log2_tab.o reverse.o
>>  OBJS-$(CONFIG_SINEWIN)                 += sinewin.o sinewin_fixed.o
>> diff --git a/libavcodec/rdft.c b/libavcodec/rdft.c
>> index c318aa8..9590673 100644
>> --- a/libavcodec/rdft.c
>> +++ b/libavcodec/rdft.c
>> @@ -28,28 +28,6 @@
>>   * (Inverse) Real Discrete Fourier Transforms.
>>   */
>>
>> -/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
>> -#if !CONFIG_HARDCODED_TABLES
>> -SINTABLE(16);
>> -SINTABLE(32);
>> -SINTABLE(64);
>> -SINTABLE(128);
>> -SINTABLE(256);
>> -SINTABLE(512);
>> -SINTABLE(1024);
>> -SINTABLE(2048);
>> -SINTABLE(4096);
>> -SINTABLE(8192);
>> -SINTABLE(16384);
>> -SINTABLE(32768);
>> -SINTABLE(65536);
>> -#endif
>> -static SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
>> -    NULL, NULL, NULL, NULL,
>> -    ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512,
>> ff_sin_1024,
>> -    ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768,
>> ff_sin_65536,
>> -};
>> -
>>  /** Map one real FFT into two parallel real even and odd FFTs. Then
>> interleave
>>   * the two real FFTs into one complex FFT. Unmangle the results.
>>   * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
>> @@ -73,20 +51,29 @@ static void rdft_calc_c(RDFTContext *s, FFTSample
>> *data)
>>      ev.re = data[0];
>>      data[0] = ev.re+data[1];
>>      data[1] = ev.re-data[1];
>> -    for (i = 1; i < (n>>2); i++) {
>> -        i1 = 2*i;
>> -        i2 = n-i1;
>> -        /* Separate even and odd FFTs */
>> -        ev.re =  k1*(data[i1  ]+data[i2  ]);
>> -        od.im = -k2*(data[i1  ]-data[i2  ]);
>> -        ev.im =  k1*(data[i1+1]-data[i2+1]);
>> -        od.re =  k2*(data[i1+1]+data[i2+1]);
>> -        /* Apply twiddle factors to the odd FFT and add to the even FFT */
>> -        data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
>> -        data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
>> -        data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
>> -        data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
>> +
>> +#define RDFT_UNMANGLE(sign0, sign1)
>>    \
>> +    for (i = 1; i < (n>>2); i++) {
>>   \
>> +        i1 = 2*i;
>>    \
>> +        i2 = n-i1;
>>   \
>> +        /* Separate even and odd FFTs */
>>   \
>> +        ev.re =  k1*(data[i1  ]+data[i2  ]);
>>     \
>> +        od.im = -k2*(data[i1  ]-data[i2  ]);
>>     \
>> +        ev.im =  k1*(data[i1+1]-data[i2+1]);
>>     \
>> +        od.re =  k2*(data[i1+1]+data[i2+1]);
>>     \
>> +        /* Apply twiddle factors to the odd FFT and add to the even FFT
>> */  \
>> +        data[i1  ] =  ev.re + od.re*tcos[i] sign0 od.im*tsin[i];
>>     \
>> +        data[i1+1] =  ev.im + od.im*tcos[i] sign1 od.re*tsin[i];
>>     \
>> +        data[i2  ] =  ev.re - od.re*tcos[i] sign1 od.im*tsin[i];
>>     \
>> +        data[i2+1] = -ev.im + od.im*tcos[i] sign1 od.re*tsin[i];
>>     \
>> +    }
>> +
>> +    if (s->inverse != (s->sign_convention == 1)) {
>> +        RDFT_UNMANGLE(-,+)
>> +    } else {
>> +        RDFT_UNMANGLE(+,-)
>>      }
>> +
>>      data[2*i+1]=s->sign_convention*data[2*i+1];
>>      if (s->inverse) {
>>          data[0] *= k1;
>> @@ -113,18 +100,11 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits,
>> enum RDFTransformType trans)
>>
>>      ff_init_ff_cos_tabs(nbits);
>>      s->tcos = ff_cos_tabs[nbits];
>> -    s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans ==
>> DFT_C2R)*(n>>2);
>> -#if !CONFIG_HARDCODED_TABLES
>> -    {
>> -        int i;
>> -        const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 :
>> 1) * 2 * M_PI / n;
>> -        for (i = 0; i < (n >> 2); i++)
>> -            s->tsin[i] = sin(i * theta);
>> -    }
>> -#endif
>> +    s->tsin = ff_cos_tabs[nbits] + (n >> 2);
>>      s->rdft_calc   = rdft_calc_c;
>>
>> -    if (ARCH_ARM) ff_rdft_init_arm(s);
>> +    // FIXME change arm implementation
>> +    //if (ARCH_ARM) ff_rdft_init_arm(s);
>>
>>
> You could just change the sintable back to what it used to be in the arm
> init function. Or you could try to figure out how to change the asm to work
> with it.

I tried to figure out how to change asm. Unfortunately I didn't test
it because I failed to setup cross compile environment. However I'll
post the patch.

Thank's.