lib/math/atan2.c

   1 /*
   2  * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
   3  * See the copyright notice in the ACK home directory, in the file "Copyright".
   4  *
   5  * Author: Ceriel J.H. Jacobs
   6  */
   7 /* $Header$ */
   8
   9 #include        <math.h>
  10 #include        <errno.h>
  11 #include        "localmath.h"
  12
  13 double
  14 atan2(double y, double x)
  15 {
  16         double absx, absy, val;
  17
  18         if (x == 0 && y == 0) {
  19                 errno = EDOM;
  20                 return 0;
  21         }
  22         absy = y < 0 ? -y : y;
  23         absx = x < 0 ? -x : x;
  24         if (absy - absx == absy) {
  25                 /* x negligible compared to y */
  26                 return y < 0 ? -M_PI_2 : M_PI_2;
  27         }
  28         if (absx - absy == absx) {
  29                 /* y negligible compared to x */
  30                 val = 0.0;
  31         }
  32         else    val = atan(y/x);
  33         if (x > 0) {
  34                 /* first or fourth quadrant; already correct */
  35                 return val;
  36         }
  37         if (y < 0) {
  38                 /* third quadrant */
  39                 return val - M_PI;
  40         }
  41         return val + M_PI;
  42 }