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45 lines
1.0 KiB
45 lines
1.0 KiB
12 years ago
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/* trig.c */
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/* Cosine implementation from:
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* http://www.ganssle.com/articles/atrig.htm
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*/
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double cosine(double x)
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{
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double p0,p1,p2,p3,p4,p5,y,t,absx,frac,pi2;
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int quad;
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p0= 0.999999999781;
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p1=-0.499999993585;
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p2= 0.041666636258;
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p3=-0.0013888361399;
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p4= 0.00002476016134;
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p5=-0.00000026051495;
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pi2=1.570796326794896; /* pi/2 */
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absx=x;
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if (x<0) absx=-absx; /* absolute value of input */
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quad=(int) (absx/pi2); /* quadrant (0 to 3) */
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if (quad > 3) {
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int q = quad & ~3; /* round down to the next multiple of 4 */
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absx = absx / (pi2 * quad);
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quad -= q;
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t = 0.0; /* hello, compiler warnings */
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}
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frac= (absx/pi2) - quad; /* fractional part of input */
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if(quad==0) t=frac * pi2;
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if(quad==1) t=(1-frac) * pi2;
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if(quad==2) t=frac * pi2;
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if(quad==3) t=(frac-1) * pi2;
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t=t * t;
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y=p0 + (p1*t) + (p2*t*t) + (p3*t*t*t) + (p4*t*t*t*t) + (p5*t*t*t*t*t);
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if(quad==2 || quad==1) y=-y; /* correct sign */
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return(y);
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};
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double sine(double x)
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{
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double pi2=1.570796326794896; /* pi/2 */
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x = x - pi2;
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if (x < -pi2) x += pi2*4;
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return cosine(x);
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}
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