Diff: fast_math.cpp

Revision:

12:a4b17bb682eb

Child:

13:791e20f1af43

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/fast_math.cpp	Fri Dec 21 22:06:56 2012 +0000
@@ -0,0 +1,51 @@
+#include "mbed.h"
+#include "fast_math.h"
+
+unsigned short  sin60[DEG60+1];  // sin table from 0 to 60 deg. (max precision error is 0.003%)
+
+long _sin(unsigned short th){    // return( 65535*sin(th) ), th=rad*DEG60/(PI/3)=rad*(512*3)/PI (0<=rad<2*PI)
+//    init_sin60();
+//    if( th>2.*PI ){ th -= 2*PI*(float)((int)(th/(2.*PI)));}
+//    th_int = (unsigned short)(th/(PI/3.)*(float)DEG60+0.5);  // rad to deg
+//    sin = (float)_sin(th)/65535.;
+    unsigned short f_minus;
+    long    x;
+
+    if( th>=DEG60*3){   f_minus = 1;    th -= DEG60*3;} // if th>=180deg, th = th - 180deg;
+    else{               f_minus = 0;}                   // else         , f_minus = on. 
+
+    if( th<DEG60 ){         // th<60deg?
+        x = sin60[th];                              // sin(th)
+    }else if( th<DEG60*2 ){ // 60<=th<120deg?
+        x = sin60[DEG60*2-th] + sin60[th-DEG60];    // sin(th)=sin(th+60)+sin(th-60)=sin(180-(th+60))+sin(th-60) because sin(th+60)=s/2+c*root(3)/2, sin(th-60)=s/2-c*root(3)/2.
+    }else{// if( th<180 )   // 120<=th<180deg?
+        x = sin60[DEG60*3-th];                      // sin(60-(th-120))=sin(180-th)
+    }
+    if( f_minus==1 ){   x = -x;}
+    return(x);
+}
+
+long _cos(unsigned short th){    // return( 65535*sin(th) ), th=rad*DEG60/(PI/3)=rad*(512*3)/PI (0<=rad<2*PI)
+    th += DEG60*3/2;
+    if( th>=DEG60*6 ){  th -= DEG60*6;}
+    return( _sin(th) );
+}
+
+void init_fast_math(){  // sin0-sin60deg; 0deg=0, 60deg=512
+    int i;
+    
+    for( i=0;i<=DEG60;i++ ){    // set sin table from 0 to 60 deg..
+//        sin60[i] = (unsigned short)(sin((float)i/512.*PI/3.));
+        sin60[i] = (unsigned short)(65535.*sinf((float)i/(float)DEG60*PI/3.));
+    }
+}
+
+#if 0
+//float  norm(float x[0], float x[1]){  // ２ノルムを計算
+//    return(sqrt(x[0]*x[0]+x[1]*x[1]));
+//}
+float  sqrt2(float x){    // √xのx=1まわりのテイラー展開 √x = 1 + 1/2*(x-1) -1/4*(x-1)^2 + ...
+//  return((1+x)*0.5);      // 一次近似
+    return(x+(1-x*x)*0.25); // 二次近似
+}
+#endif
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