atan2pi

eve::atan2pi = functor<atan2pi_t>

inlineconstexpr

Header file

#include <eve/module/core.hpp>

Callable Signatures

namespace eve
{
   // Regular overload
   constexpr auto atan2pi(floating_value auto x, floating_value auto y)                          noexcept; // 1
 
   // Semantic option
   constexpr auto atan2pi[pedantic](floating_value auto x, floating_value auto y)                noexcept; // 2
 
   // Lanes masking
   constexpr auto atan2pi[conditional_expr auto c][floating_value auto x, floating_value auto y) noexcept; // 3
   constexpr auto atan2pi[logical_value auto m](floating_value auto x, floating_value auto y)    noexcept; // 3
}

Parameters

• x, y: floating values.
• c: Conditional expression masking the operation.
• m: Logical value masking the operation.

Return value

1. the arc tangent of $\frac{y}x$ in $\pi$, in the range [-1, +1], is returned. The IEEE limiting values are almost all satisfied :

   • If x and y are both zero or infinites, Nan is returned (this is not standard conforming)
   • If y is $\pm0$ and x is strictly negative or $-0$, $\pm1$ is returned
   • If y is $\pm0$ and x is strictly positive or $+0$, $\pm0$ is returned
   • If y is $\pm\infty$ and x is finite, $\pm\frac12$ is returned
   • If x is $\pm0$ and y is strictly negative, $-\frac12$ is returned
   • If x is $\pm0$ and y is strictly positive, $+\frac12$ is returned
   • If x is $-\infty$ and y is finite and positive, $+1$ is returned
   • If x is $-\infty$ and y is finite and negative, $-1$ is returned
   • If x is $+\infty$ and y is finite and positive, $+0$ is returned
   • If x is $+\infty$ and y is finite and negative, $-0$ is returned
   • If either x is Nan or y is Nan, Nan is returned

   The call will return a NaN if x and y are both either null or infinite: this result is not IEEE conformant, but allows to simplify (and speed) the implementation. In all other cases, the result is standard conformant.

2. Same as 1, except that all IEEE limiting values are satisfied :
   • If y is $\pm\infty$ and x is $-\infty$, $\pm\frac34$ is returned
   • If y is $\pm\infty$ and x is $+\infty$, $\pm\frac14$ is returned
   • If x is $\pm0$ and y is $\pm-0$, $-\frac12$ is returned
   • If x is $\pm0$ and y is $\pm+0$, $+\frac12$ is returned
3. The operation is performed conditionnaly.

External references

• C++ standard reference:atan2
• Wolfram MathWorld: Inverse Tangent
• Wikipedia: Atan2

Example

// revision 1
#include <eve/module/math.hpp>
#include <iostream> 
 
int main()
{ 
  eve::wide pf = { 0.0f, 1.0f, 4.0f, -2.0f, eve::inf(eve::as<float>()), 0.0f, eve::minf(eve::as<float>()), 1.0f};
  eve::wide qf = { 1.0f, -1.0f, 3.0f, -0.0f, 1.0f, 0.0f, 0.0f, -0.0f};
 
  std::cout << "<- pf                             = " << pf << "\n";
  std::cout << "<- qf                             = " << qf << "\n";
 
  std::cout << "-> atan2pi(pf, qf)                = " << eve::atan2pi(pf, qf) << "\n";
  std::cout << "-> atan2pi[pedantic](pf, qf)      = " << eve::atan2pi[eve::pedantic](pf, qf) << "\n";
  std::cout << "-> atan2pi[ignore_last(2)](pf, qf)= " << eve::atan2pi[eve::ignore_last(2)](pf, qf) << "\n";
  std::cout << "-> atan2pi[pf != -2.0f](pf, qf)   = " << eve::atan2pi[pf != -2.0f](pf, qf) << "\n";
}