first_true

eve::first_true = {}

inlineconstexpr

#include <eve/module/core.hpp>

Should you check for any?

The function is considering the case when nothing is set to be likely, checking for eve::any before hand is not going to be helpful. At the moment there isn't a function that would do it otherwise.

What if I know there is a match?

We would recommend *evefirst_true(m) - this is likely to trigger compiler optimizations, based on it being UB otherwise.

Callable Signatures

template <logical_simd_value L>
std::optional<std::ptrdiff_t> first_true(L m);  // (1)
 
template <logical_simd_value L>
std::optional<std::ptrdiff_t> first_true(top_bits<L> m);    // (2)
 
template <relative_conditional_expr C, logical_simd_value L>
std::optional<std::ptrdiff_t> first_true[C ignore](L m);    // (3)
 
std::optional<std::ptrdiff_t> first_true(bool m);  // (4)

Parameters

• m - logical_value or top_bits where to find first true value
• ignore - ignored elements are considered false. Only supported for logical_simd_value

Return value

Returns std::nullopt if eve::none(m). Otherwise returns 0 based index.

Example

// revision 0
#include <eve/module/core.hpp>
#include <iostream>
 
int main()
{
  eve::wide wu0{0u, 1u, 2u, 3u, 4u, 5u, 6u, 7u};
 
  std::cout << "<- wu0                                                      = " << wu0 << "\n";
 
  std::cout << "-> first_true(wu0 >= maximum(wu0)/2)                        = " << *eve::first_true(wu0 >= eve::maximum(wu0)/2) << "\n";
  std::cout << "-> first_true[ignore_first(4)](wu0 <= maximum(wu0)/2 >  1u) = " << *eve::first_true[eve::ignore_first(4)](wu0 > 1u) << "\n";
}