Call rdft by function pointer

Call the RDFT by a function pointer like other FFT related transforms.
This makes instruction set optimized versions possible.

Based on patch by Alex Converse.

Originally committed as revision 22609 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/fft.h

@@ -196,6 +196,7 @@ struct RDFTContext {
     const FFTSample *tcos;
     SINTABLE_CONST FFTSample *tsin;
     FFTContext fft;
+    void (*rdft_calc)(struct RDFTContext *s, FFTSample *z);
 };
 
 /**
@@ -204,9 +205,13 @@ struct RDFTContext {
  * @param trans           the type of transform
  */
 int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans);
-void ff_rdft_calc(RDFTContext *s, FFTSample *data);
 void ff_rdft_end(RDFTContext *s);
 
+static av_always_inline void ff_rdft_calc(RDFTContext *s, FFTSample *data)
+{
+    s->rdft_calc(s, data);
+}
+
 /* Discrete Cosine Transform */
 
 struct DCTContext {

libavcodec/rdft.c

@@ -50,6 +50,8 @@ SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
     ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
 };
 
+static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data);
+
 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
 {
     int n = 1 << nbits;
@@ -74,6 +76,7 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
         s->tsin[i] = sin(i*theta);
     }
 #endif
+    s->rdft_calc   = ff_rdft_calc_c;
     return 0;
 }
 
@@ -123,11 +126,6 @@ static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
     }
 }
 
-void ff_rdft_calc(RDFTContext *s, FFTSample *data)
-{
-    ff_rdft_calc_c(s, data);
-}
-
 av_cold void ff_rdft_end(RDFTContext *s)
 {
     ff_fft_end(&s->fft);