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98 lines
2.2 KiB
98 lines
2.2 KiB
#include <soft.h>
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/*
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floating-point arctangent
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atan returns the value of the arctangent of its
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argument in the range [-pi/2,pi/2].
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atan2 returns the arctangent of arg1/arg2
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in the range [-pi,pi].
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there are no error returns.
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coefficients are #5077 from Hart & Cheney. (19.56D)
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*/
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double pio2 = 1.570796326794896619;
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static double sq2p1 =2.414213562373095048802e0;
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static double sq2m1 = .414213562373095048802e0;
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static double pio4 = .785398163397448309615e0;
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static double p4 = .161536412982230228262e2;
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static double p3 = .26842548195503973794141e3;
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static double p2 = .11530293515404850115428136e4;
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static double p1 = .178040631643319697105464587e4;
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static double p0 = .89678597403663861959987488e3;
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static double q4 = .5895697050844462222791e2;
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static double q3 = .536265374031215315104235e3;
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static double q2 = .16667838148816337184521798e4;
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static double q1 = .207933497444540981287275926e4;
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static double q0 = .89678597403663861962481162e3;
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static double satan(double);
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static double xatan(double);
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/*
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atan makes its argument positive and
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calls the inner routine satan.
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*/
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double atan(double arg)
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{
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if(arg>0)
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return(satan(arg));
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else
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return(-satan(-arg));
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}
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/*
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atan2 discovers what quadrant the angle
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is in and calls atan.
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*/
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double atan2(double arg1, double arg2)
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{
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if((arg1+arg2)==arg1)
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if(arg1 >= 0.) return(pio2);
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else return(-pio2);
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else if(arg2 <0.)
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if(arg1 >= 0.)
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return(pio2+pio2 - satan(-arg1/arg2));
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else
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return(-pio2-pio2 + satan(arg1/arg2));
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else if(arg1>0)
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return(satan(arg1/arg2));
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return(-satan(-arg1/arg2));
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}
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/*
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satan reduces its argument (known to be positive)
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to the range [0,0.414...] and calls xatan.
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*/
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static double satan(double arg)
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{
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if(arg < sq2m1)
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return(xatan(arg));
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else if(arg > sq2p1)
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return(pio2 - xatan(1.0/arg));
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return(pio4 + xatan((arg-1.0)/(arg+1.0)));
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}
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/*
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xatan evaluates a series valid in the
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range [-0.414...,+0.414...].
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*/
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static double xatan(double arg)
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{
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double argsq;
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double value;
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argsq = arg*arg;
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value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
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value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
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return(value*arg);
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}
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