/*	floating-point arctangent 	atan returns the value of the arctangent of its	argument in the range [-pi/2,pi/2]. 	atan2 returns the arctangent of arg1/arg2	in the range [-pi,pi]. 	there are no error returns. 	coefficients are #5077 from Hart & Cheney. (19.56D)*/ #include <u.h>#include <libc.h> #define sq2p1 2.414213562373095048802e0#define sq2m1  .414213562373095048802e0#define p4  .161536412982230228262e2#define p3  .26842548195503973794141e3#define p2  .11530293515404850115428136e4#define p1  .178040631643319697105464587e4#define p0  .89678597403663861959987488e3#define q4  .5895697050844462222791e2#define q3  .536265374031215315104235e3#define q2  .16667838148816337184521798e4#define q1  .207933497444540981287275926e4#define q0  .89678597403663861962481162e3  /*	xatan evaluates a series valid in the	range [-0.414...,+0.414...]. (tan(pi/8)) */ staticdoublexatan(double arg){	double argsq, value; 	argsq = arg*arg;	value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);	value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);	return value*arg;} /*	satan reduces its argument (known to be positive)	to the range [0,0.414...] and calls xatan. */ staticdoublesatan(double arg){ 	if(arg < sq2m1)		return xatan(arg);	if(arg > sq2p1)		return PIO2 - xatan(1/arg);	return PIO2/2 + xatan((arg-1)/(arg+1));} /*	atan makes its argument positive and	calls the inner routine satan. */ doubleatan(double arg){ 	if(arg > 0)		return satan(arg);	return -satan(-arg);}