From f6f2822caad3cda4e8512a50ee0b4607257e7d06 Mon Sep 17 00:00:00 2001
From: Buschel <Buschel@a1c6a512-1295-4272-9138-f99709370657>
Date: Mon, 15 Feb 2010 13:00:02 +0000
Subject: [PATCH] Work on atrac Joint Stereo mode. Correct calculation in
 getChannelWeights(), introduce lookup table and remove obsolete code.
 Optimize interpolation macro.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24665 a1c6a512-1295-4272-9138-f99709370657
---
 apps/codecs/libatrac/atrac3.c           | 31 +++++++++++++++++-------
 apps/codecs/libatrac/atrac3data_fixed.h | 12 +++++++++
 apps/codecs/libatrac/fixp_math.h        | 43 ---------------------------------
 3 files changed, 34 insertions(+), 52 deletions(-)

diff --git a/apps/codecs/libatrac/atrac3.c b/apps/codecs/libatrac/atrac3.c
index 467f42f16..5ff3a8587 100644
--- a/apps/codecs/libatrac/atrac3.c
+++ b/apps/codecs/libatrac/atrac3.c
@@ -628,8 +628,21 @@ static int addTonalComponents (int32_t *pSpectrum, int numComponents, tonal_comp
     return lastPos;
 }
 
-
-#define INTERPOLATE(old,new,nsample)  ((old*ONE_16) + fixmul16(((nsample*ONE_16)>>3), (((new) - (old))*ONE_16)))
+/**
+ * Linear equidistant interpolation between two points x and y. 7 interpolation
+ * points can be calculated. Result is scaled by <<16.
+ * Result for s=0 is x*ONE_16
+ * Result for s=8 is y*ONE_16
+ *
+ * @param x     first input point
+ * @param y     second input point
+ * @param s     index of interpolation point (0..7)
+ */
+ 
+/*
+#define INTERPOLATE(x, y, s)    ((x*ONE_16) + fixmul16(((s*ONE_16)>>3), (((x) - (y))*ONE_16)))
+*/
+#define INTERPOLATE(x, y, s)    ((((x)<<3) + s*((y)-(x)))<<13)
 
 static void reverseMatrixing(int32_t *su1, int32_t *su2, int *pPrevCode, int *pCurrCode)
 {
@@ -695,14 +708,14 @@ static void reverseMatrixing(int32_t *su1, int32_t *su2, int *pPrevCode, int *pC
 }
 
 static void getChannelWeights (int indx, int flag, int32_t ch[2]){
-    if (indx == 7) {
-        ch[0] = ONE_16;
-        ch[1] = ONE_16;
+    /* Read channel weights from table */
+    if (flag) {
+        /* Swap channel weights */
+        ch[1] = channelWeights0[indx&7];
+        ch[0] = channelWeights1[indx&7];
     } else {
-        ch[0] = fixdiv16(((indx & 7)*ONE_16), 7*ONE_16);
-        ch[1] = fastSqrt((ONE_16 << 1) - fixmul16(ch[0], ch[0]));
-        if(flag)
-            FFSWAP(int32_t, ch[0], ch[1]);
+        ch[0] = channelWeights0[indx&7];
+        ch[1] = channelWeights1[indx&7];
     }
 }
 
diff --git a/apps/codecs/libatrac/atrac3data_fixed.h b/apps/codecs/libatrac/atrac3data_fixed.h
index f0924a519..d73ded35f 100644
--- a/apps/codecs/libatrac/atrac3data_fixed.h
+++ b/apps/codecs/libatrac/atrac3data_fixed.h
@@ -80,3 +80,15 @@ static const int32_t matrixCoeffs_fix[8] ICONST_ATTR = {
     0x00000000, 0x00000000, 0x00010000, 0x00010000, 
 };
 
+/* channelWeights0[i] = ONE_16 * ((i & 7)/7) */
+static const int32_t channelWeights0[8] ICONST_ATTR = {
+    0x00000000, 0x00002492, 0x00004925, 0x00006DB7,
+    0x00009249, 0x0000B6DB, 0x0000DB6D, 0x00010000,
+};
+
+/* channelWeights1[i] = ONE_16 * sqrt(2-channelWeights0^2) */
+static const int32_t channelWeights1[8] ICONST_ATTR = {
+    0x00016A0A, 0x00016830, 0x00016293, 0x00015904,
+    0x00014B2B, 0x00013877, 0x00011FF7, 0x00010000,
+};
+
diff --git a/apps/codecs/libatrac/fixp_math.h b/apps/codecs/libatrac/fixp_math.h
index 5174cc7cc..29d47a9e5 100644
--- a/apps/codecs/libatrac/fixp_math.h
+++ b/apps/codecs/libatrac/fixp_math.h
@@ -91,46 +91,3 @@
         return (int32_t)temp;
     }
 #endif
-
-static inline int32_t fixdiv16(int32_t x, int32_t y)
-{
-    int64_t temp;
-    temp = x << 16;
-    temp /= y;
-
-    return (int32_t)temp;
-}
-
-/*
- * Fast integer square root adapted from algorithm, 
- * Martin Guy @ UKC, June 1985.
- * Originally from a book on programming abaci by Mr C. Woo.
- * This is taken from :
- * http://wiki.forum.nokia.com/index.php/How_to_use_fixed_point_maths#How_to_get_square_root_for_integers
- * with a added shift up of the result by 8 bits to return result in 16.16 fixed-point representation.
- */
-static inline int32_t fastSqrt(int32_t n)
-{
-   /*
-    * Logically, these are unsigned. 
-    * We need the sign bit to test
-    * whether (op - res - one) underflowed.
-    */
-    int32_t op, res, one;
-    op = n;
-    res = 0;
-    /* "one" starts at the highest power of four <= than the argument. */
-    one = 1 << 30; /* second-to-top bit set */
-    while (one > op) one >>= 2;
-    while (one != 0) 
-    {
-        if (op >= res + one) 
-        {
-            op = op - (res + one);
-            res = res +  (one<<1);
-        }
-        res >>= 1;
-        one >>= 2;
-    }
-    return(res << 8);
-}
-- 
2.11.4.GIT