avcodec/rdft: remove sintable

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, in
C code and ARM assembly code.

Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>

1 files changed, 24 insertions, 44 deletions

diff --git a/libavcodec/rdft.c b/libavcodec/rdft.c
index c318aa8394..194e0bc4ee 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->negative_sin) {
+        RDFT_UNMANGLE(+,-)
+    } else {
+        RDFT_UNMANGLE(-,+)
     }
+
     data[2*i+1]=s->sign_convention*data[2*i+1];
     if (s->inverse) {
         data[0] *= k1;
@@ -104,6 +91,7 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
     s->nbits           = nbits;
     s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
     s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
+    s->negative_sin    = trans == DFT_C2R || trans == DFT_R2C;
 
     if (nbits < 4 || nbits > 16)
         return AVERROR(EINVAL);
@@ -113,15 +101,7 @@ 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);