vu_meter: Use the fixedpoint lib (moving flog there)

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@14103 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 30 insertions, 0 deletions

diff --git a/apps/plugins/lib/fixedpoint.c b/apps/plugins/lib/fixedpoint.c
index cf69d9c..88c2f6e 100644
--- a/apps/plugins/lib/fixedpoint.c
+++ b/apps/plugins/lib/fixedpoint.c
@@ -202,3 +202,33 @@ long cos_int(int val)
     }
     return 0;
 }
+
+/**
+ * Fixed-point natural log
+ * taken from http://www.quinapalus.com/efunc.html
+ *  "The code assumes integers are at least 32 bits long. The (positive)
+ *   argument and the result of the function are both expressed as fixed-point
+ *   values with 16 fractional bits, although intermediates are kept with 28
+ *   bits of precision to avoid loss of accuracy during shifts."
+ */
+
+long flog(int x) {
+    long t,y;
+
+    y=0xa65af;
+    if(x<0x00008000) x<<=16,              y-=0xb1721;
+    if(x<0x00800000) x<<= 8,              y-=0x58b91;
+    if(x<0x08000000) x<<= 4,              y-=0x2c5c8;
+    if(x<0x20000000) x<<= 2,              y-=0x162e4;
+    if(x<0x40000000) x<<= 1,              y-=0x0b172;
+    t=x+(x>>1); if((t&0x80000000)==0) x=t,y-=0x067cd;
+    t=x+(x>>2); if((t&0x80000000)==0) x=t,y-=0x03920;
+    t=x+(x>>3); if((t&0x80000000)==0) x=t,y-=0x01e27;
+    t=x+(x>>4); if((t&0x80000000)==0) x=t,y-=0x00f85;
+    t=x+(x>>5); if((t&0x80000000)==0) x=t,y-=0x007e1;
+    t=x+(x>>6); if((t&0x80000000)==0) x=t,y-=0x003f8;
+    t=x+(x>>7); if((t&0x80000000)==0) x=t,y-=0x001fe;
+    x=0x80000000-x;
+    y-=x>>15;
+    return y;
+}