Synopsis

#include <math.h>

double atan2(double y, double x);

float atan2f(float y, float x);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

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, ± shall be returned.

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

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

  • If y is > 0 and x is ±0, /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 correct value would cause underflow, a range error may occur, and atan(), atan2f(), and atan2l() shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

  • If the IEC 60559 Floating-Point option is supported, y/x should be returned.

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

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

  • If y is ±Inf and x is +Inf, ±/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.

Tests

Untested

Known bugs

None

See Also

  1. Standard library functions
  2. Table of Contents