log2

auto eve::log2 = functor<log2_t>

inlineconstexpr

Callable Signatures

#include <eve/module/math.hpp>

Callable Signatures

namespace eve
{
   // Regular overload
   constexpr auto log2(floating_value auto x)                          noexcept; // 1
 
   // Lanes masking
   constexpr auto log2[conditional_expr auto c](floating_value auto x) noexcept; // 2
   constexpr auto log2[logical_value auto m](floating_value auto x)    noexcept; // 2
}

Parameters

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

Return value

1. Returns the elementwise the base 2 logarithm of x In particular, for floating inputs:
   • If the element is \(\pm0\), \(-\infty\) is returned.
   • If the element is \(1\), \(+0\) is returned.
   • If the element is \(\infty\), \(\infty\) is returned.
   • If the element is less than 0, NaN is returned.
2. The operation is performed conditionnaly.

External references

• C++ standard reference
• Wolfram MathWorld
• Wikipedia

Example

// revision 1
#include <eve/module/math.hpp>
#include <iostream>
 
int main()
{
  eve::wide wf = {0.0f, -0.0f, -1.0f, 1.0f, 2.0f,
                  eve::inf(eve::as<float>()), 4.0f, eve::nan(eve::as<float>())};
 
  std::cout << "<- wf                      = " << wf << "\n";
 
  std::cout << "-> log2(wf)                = " << eve::log2(wf) << "\n";
  std::cout << "-> log2[ignore_last(2)](wf)= " << eve::log2[eve::ignore_last(2)](wf) << "\n";
  std::cout << "-> log2[wf != 2.0f](wf)    = " << eve::log2[wf != 2.0f](wf) << "\n";
}

• Masked Call

  The call eve::log2[mask](x) provides a masked version of eve::log2 which is equivalent to if_else (mask, log2(x), x).

  Example

  #include <eve/module/math.hpp>
  #include <eve/wide.hpp>
  #include <iostream>
   
  using wide_ft = eve::wide<float, eve::fixed<8>>;
   
  int main()
  {
    wide_ft pf = {0.0f, -0.0f, -1.0f, 1.0f, 2.0f,
                 eve::inf(eve::as<float>()), 4.0f, eve::nan(eve::as<float>())};
   
    std::cout << "---- simd" << '\n'
              << "<- pf             = " << pf << '\n'
              << "-> log2[pf > 1.0](pf)       = " << eve::log2[pf > 1.0](pf) << '\n';
    return 0;
  }