trusty (3) atan2l.3posix.gz

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NAME
       atan2, atan2f, atan2l - arc tangent functions


SYNOPSIS
       #include <math.h>

       double atan2(double y, double x);
       float atan2f(float y, float x);
       long double atan2l(long double y, long double x);


DESCRIPTION
       These  functions  shall  compute  the principal value of the arc tangent of y/ x, using the signs of both
       arguments to determine the quadrant of the return value.

       An  application  wishing  to  check  for  error  situations  should  set   errno   to   zero   and   call
       feclearexcept(FE_ALL_EXCEPT)  before  calling  these  functions.   On  return,  if  errno  is non-zero or
       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.


RETURN VALUE
       Upon successful completion, these functions shall return the arc tangent of y/ x in  the  range  [-pi,pi]
       radians.

       If y is ±0 and x is < 0, ±pi shall be returned.

       If y is ±0 and x is > 0, ±0 shall be returned.

       If y is < 0 and x is ±0, -pi/2 shall be returned.

       If y is > 0 and x is ±0, pi/2 shall be returned.

       If x is 0, a pole error shall not occur.

       If either x or y is NaN, a NaN shall be returned.

       If the result underflows, a range error may occur and y/ x should be returned.

       If y is ±0 and x is -0, ±pi shall be returned.

       If y is ±0 and x is +0, ±0 shall be returned.

       For finite values of ± y > 0, if x is -Inf, ±pi shall be returned.

       For finite values of ± y > 0, if x is +Inf, ±0 shall be returned.

       For finite values of x, if y is ±Inf, ±pi/2 shall be returned.

       If y is ±Inf and x is -Inf, ±3pi/4 shall be returned.

       If y is ±Inf and x is +Inf, ±pi/4 shall be returned.

       If both arguments are 0, a domain error shall not occur.


ERRORS
       These functions may fail if:

       Range Error
              The result underflows.

       If  the  integer  expression  (math_errhandling  &  MATH_ERRNO)  is  non-zero, then errno shall be set to
       [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then  the  underflow
       floating-point exception shall be raised.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       On  error,  the  expressions  (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are
       independent of each other, but at least one of them must be non-zero.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       atan() ,  feclearexcept()  ,  fetestexcept()  ,  isnan()  ,  tan()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .