94 lines
2 KiB
C
94 lines
2 KiB
C
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/*
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* (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
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*
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* This product is part of the Amsterdam Compiler Kit.
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*
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* Permission to use, sell, duplicate or disclose this software must be
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* obtained in writing. Requests for such permissions may be sent to
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*
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* Dr. Andrew S. Tanenbaum
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* Wiskundig Seminarium
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* Vrije Universiteit
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* Postbox 7161
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* 1007 MC Amsterdam
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* The Netherlands
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*
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*/
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/* $Header $ */
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/* Author: J.W. Stevenson */
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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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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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static double sq2p1 = 2.414213562373095048802e0;
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static double sq2m1 = .414213562373095048802e0;
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static double pio2 = 1.570796326794896619231e0;
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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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/*
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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
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xatan(arg)
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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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static double
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satan(arg)
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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/arg));
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else
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return(pio4 + xatan((arg-1)/(arg+1)));
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}
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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
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_atn(arg)
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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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