From 432e2ecc137d4fb4d9f6ac87cbbc38830a1f3c2c Mon Sep 17 00:00:00 2001
From: Mohamed Tarek <mt@rockbox.org>
Date: Thu, 13 Aug 2009 20:38:59 +0000
Subject: Modify libatrac to use fixed-point arithmetic.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@22298 a1c6a512-1295-4272-9138-f99709370657
---
 apps/codecs/libatrac/fixp_math.c | 66 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 apps/codecs/libatrac/fixp_math.c

(limited to 'apps/codecs/libatrac/fixp_math.c')

diff --git a/apps/codecs/libatrac/fixp_math.c b/apps/codecs/libatrac/fixp_math.c
new file mode 100644
index 0000000000..3f578a1ade
--- /dev/null
+++ b/apps/codecs/libatrac/fixp_math.c
@@ -0,0 +1,66 @@
+#include "fixp_math.h"
+
+inline int32_t fixmul31(int32_t x, int32_t y)
+{
+    int64_t temp;
+    temp = x;
+    temp *= y;
+
+    temp >>= 31;        //16+31-16 = 31 bits
+
+    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.
+ */
+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);
+}
+
+inline int32_t fixmul16(int32_t x, int32_t y)
+{
+    int64_t temp;
+    temp = x;
+    temp *= y;
+
+    temp >>= 16;
+
+    return (int32_t)temp;
+}
+
+inline int32_t fixdiv16(int32_t x, int32_t y)
+{
+    int64_t temp;
+    temp = x << 16;
+    temp /= y;
+
+    return (int32_t)temp;
+}
-- 
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