Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!oberon!sm.unisys.com!csun!solaria!ecphssrw@afws.csun.edu
From: ecphssrw@afws.csun.edu (Stephen Walton)
Newsgroups: comp.sys.amiga
Subject: Re: atan2 sources (clarification)
Summary: Here's one, and it wasn't hard to write.
Message-ID: <495@solaria.csun.edu>
Date: 23 Feb 89 21:44:08 GMT
References: <1991@pur-phy>
Sender: ecphssrw@solaria.csun.edu
Reply-To: ecphssrw@afws.csun.edu (Stephen Walton)
Organization: California State Univ., Northridge
Lines: 34
In-reply-to: murphy@pur-phy (William J. Murphy)

This took about ten minutes, counting testing.  Based on the manual
entry for Microsoft C's atan2 (which is all I had around), but the
code itself is entirely PD (in fact, I just wrote and tested it
against the system atan2()).

/* myatan2 */

#include <errno.h>
#include <stdio.h>
#include <math.h>
#define PI 3.14159265359
extern int errno;

double myatan2(y, x)
double y, x; {
    double atan();

    if (x == 0.0) {
        if (y == 0.0) {
	    errno = EDOM;
	    fputs("atan2: DOMAIN error\n", stderr);
	    return(0.0);
        } else if (y > 0.0)
            return(PI/2.0);
        else
            return(-PI/2.0);
    } else if (x > 0)
        return(atan(y/x));
    else
        if (y >= 0.0)
            return(atan(y/x) + PI);
        else
            return(atan(y/x) - PI);
}