From 176c142abcbfda1cc161ca8614ab07dffe505349 Mon Sep 17 00:00:00 2001
From: Benjamin Larsson <banan@ludd.ltu.se>
Date: Sat, 22 Apr 2006 21:21:16 +0000
Subject: [PATCH] Patch to generate the ac3 window, based on code by Justin
 Ruggles.

Originally committed as revision 5310 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/ac3enc.c | 47 +++++++++++++++++++++++++++++++++++++++++++++
 libavcodec/ac3tab.h | 41 +++------------------------------------
 2 files changed, 50 insertions(+), 38 deletions(-)

diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
index 5ec8b4f5ac..a587c647b5 100644
--- a/libavcodec/ac3enc.c
+++ b/libavcodec/ac3enc.c
@@ -81,6 +81,51 @@ static inline int16_t fix15(float a)
     return v;
 }
 
+
+/**
+ * Generate a Kaiser Window.
+ */
+static void k_window_init(int alpha, double *window, int n, int iter)
+{
+    int j, k;
+    double a, x;
+    a = alpha * M_PI / n;
+    a = a*a;
+    for(k=0; k<n; k++) {
+        x = k * (n - k) * a;
+        window[k] = 1.0;
+        for(j=iter; j>0; j--) {
+            window[k] = (window[k] * x / (j*j)) + 1.0;
+        }
+    }
+}
+
+/**
+ * Generate a Kaiser-Bessel Derived Window.
+ * @param alpha  determines window shape
+ * @param window array to fill with window values
+ * @param iter   number of iterations to use in BesselI0
+ */
+
+static void kbd_window_init(int alpha, int16_t *out_window, int iter)
+{
+    int k, n2;
+    double kwindow[256];
+    double window[256];
+
+    n2 = 256;
+    k_window_init(alpha, kwindow, n2, iter);
+    window[0] = kwindow[0];
+    for(k=1; k<n2; k++) {
+        window[k] = window[k-1] + kwindow[k];
+    }
+    for(k=0; k<n2; k++) {
+        window[k] = sqrt(window[k] / (window[n2-1]+1));
+        //out_window[k] = round(window[k]*((1<<15)-1)); //enable this for a rounded window
+        out_window[k] = fix15(window[k]);
+    }
+}
+
 static inline int calc_lowcomp1(int a, int b0, int b1)
 {
     if ((b0 + 256) == b1) {
@@ -882,6 +927,8 @@ static int AC3_encode_init(AVCodecContext *avctx)
     ac3_common_init();
 
     /* mdct init */
+    kbd_window_init(5.0, ac3_window, 50);
+
     fft_init(MDCT_NBITS - 2);
     for(i=0;i<N/4;i++) {
         alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)N;
diff --git a/libavcodec/ac3tab.h b/libavcodec/ac3tab.h
index d8771fbeee..3621b87a71 100644
--- a/libavcodec/ac3tab.h
+++ b/libavcodec/ac3tab.h
@@ -12,44 +12,6 @@ static const uint16_t ac3_bitratetab[19] = {
     160, 192, 224, 256, 320, 384, 448, 512, 576, 640
 };
 
-/* AC3 MDCT window */
-
-/* MDCT window */
-static const int16_t ac3_window[256] = {
-    4,    7,   12,   16,   21,   28,   34,   42,
-   51,   61,   72,   84,   97,  111,  127,  145,
-  164,  184,  207,  231,  257,  285,  315,  347,
-  382,  419,  458,  500,  544,  591,  641,  694,
-  750,  810,  872,  937, 1007, 1079, 1155, 1235,
- 1318, 1406, 1497, 1593, 1692, 1796, 1903, 2016,
- 2132, 2253, 2379, 2509, 2644, 2783, 2927, 3076,
- 3230, 3389, 3552, 3721, 3894, 4072, 4255, 4444,
- 4637, 4835, 5038, 5246, 5459, 5677, 5899, 6127,
- 6359, 6596, 6837, 7083, 7334, 7589, 7848, 8112,
- 8380, 8652, 8927, 9207, 9491, 9778,10069,10363,
-10660,10960,11264,11570,11879,12190,12504,12820,
-13138,13458,13780,14103,14427,14753,15079,15407,
-15735,16063,16392,16720,17049,17377,17705,18032,
-18358,18683,19007,19330,19651,19970,20287,20602,
-20914,21225,21532,21837,22139,22438,22733,23025,
-23314,23599,23880,24157,24430,24699,24964,25225,
-25481,25732,25979,26221,26459,26691,26919,27142,
-27359,27572,27780,27983,28180,28373,28560,28742,
-28919,29091,29258,29420,29577,29729,29876,30018,
-30155,30288,30415,30538,30657,30771,30880,30985,
-31086,31182,31274,31363,31447,31528,31605,31678,
-31747,31814,31877,31936,31993,32046,32097,32145,
-32190,32232,32272,32310,32345,32378,32409,32438,
-32465,32490,32513,32535,32556,32574,32592,32608,
-32623,32636,32649,32661,32671,32681,32690,32698,
-32705,32712,32718,32724,32729,32733,32737,32741,
-32744,32747,32750,32752,32754,32756,32757,32759,
-32760,32761,32762,32763,32764,32764,32765,32765,
-32766,32766,32766,32766,32767,32767,32767,32767,
-32767,32767,32767,32767,32767,32767,32767,32767,
-32767,32767,32767,32767,32767,32767,32767,32767,
-};
-
 static uint8_t masktab[253];
 
 static const uint8_t latab[260]= {
@@ -176,6 +138,9 @@ static const uint8_t bndsz[50]={
 
 static uint8_t bndtab[51];
 
+/* AC3 MDCT window */
+static int16_t ac3_window[256];
+
 /* fft & mdct sin cos tables */
 static int16_t costab[64];
 static int16_t sintab[64];