Make the Kaiser-Bessel window generator a common function

Patch by Robert Swain, robert d swain a gmail d com

Originally committed as revision 11514 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -196,30 +196,6 @@ typedef struct {
     AVCodecContext *avctx;                  ///< parent context
 } AC3DecodeContext;
 
-/**
- * Generate a Kaiser-Bessel Derived Window.
- */
-static void ac3_window_init(float *window)
-{
-   int i, j;
-   double sum = 0.0, bessel, tmp;
-   double local_window[256];
-   double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
-
-   for (i = 0; i < 256; i++) {
-       tmp = i * (256 - i) * alpha2;
-       bessel = 1.0;
-       for (j = 100; j > 0; j--) /* default to 100 iterations */
-           bessel = bessel * tmp / (j * j) + 1;
-       sum += bessel;
-       local_window[i] = sum;
-   }
-
-   sum++;
-   for (i = 0; i < 256; i++)
-       window[i] = sqrt(local_window[i] / sum);
-}
-
 /**
  * Symmetrical Dequantization
  * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
@@ -301,7 +277,7 @@ static int ac3_decode_init(AVCodecContext *avctx)
     ac3_tables_init();
     ff_mdct_init(&s->imdct_256, 8, 1);
     ff_mdct_init(&s->imdct_512, 9, 1);
-    ac3_window_init(s->window);
+    ff_kbd_window_init(s->window);
     dsputil_init(&s->dsp, avctx);
     av_init_random(0, &s->dith_state);
 

libavcodec/dsputil.h

@@ -645,6 +645,12 @@ typedef struct MDCTContext {
     FFTContext fft;
 } MDCTContext;
 
+/**
+ * Generate a Kaiser-Bessel Derived Window.
+ * @param   window  pointer to half window
+ */
+void ff_kbd_window_init(float *window);
+
 int ff_mdct_init(MDCTContext *s, int nbits, int inverse);
 void ff_imdct_calc(MDCTContext *s, FFTSample *output,
                 const FFTSample *input, FFTSample *tmp);

libavcodec/mdct.c

@@ -25,6 +25,28 @@
  * MDCT/IMDCT transforms.
  */
 
+// Generate a Kaiser-Bessel Derived Window.
+void ff_kbd_window_init(float *window)
+{
+   int i, j;
+   double sum = 0.0, bessel, tmp;
+   double local_window[256];
+   double alpha2 = (5.0 * M_PI / 256.0) * (5.0 * M_PI / 256.0);
+
+   for (i = 0; i < 256; i++) {
+       tmp = i * (256 - i) * alpha2;
+       bessel = 1.0;
+       for (j = 100; j > 0; j--) /* default to 100 iterations */
+           bessel = bessel * tmp / (j * j) + 1;
+       sum += bessel;
+       local_window[i] = sum;
+   }
+
+   sum++;
+   for (i = 0; i < 256; i++)
+       window[i] = sqrt(local_window[i] / sum);
+}
+
 /**
  * init MDCT or IMDCT computation.
  */