Hello everybody,

Problem: Find the first set bit in a bitset with index >= a given pos
Current Solution: Run a simple loop over bits.
Preferred solution: Run a loop over words instead of bits. libstdc++ implements this extension as _Find_next() [1].

Preferred solution is 90x faster [2] than its counterpart. Due of lack of standard functionality users have to either use pick a horribly slow solution or hope for vendor's extension.

Proposal: Add a new member into std::bitset, which can be naively written as:

constexpr std::size_t find_first_set(std::size_t pos = 0) const {
  if (pos >= size()) {
    throw std::out_of_range("pos >= size");
  }
  for (; pos < size(); ++pos) {
    if ((*this)[pos])
      break;
  }
  return pos;
}

PS: libstdc++ has _Find_next(std::size_t pos) and _Find_first() but this proposal combines both of them into a single function.

References: 
1. https://gcc.gnu.org/onlinedocs/gcc-4.6.2/libstdc++/api/a01157.html#ga3b2e24c78223cf8a7db566f56eadc144
2. https://quick-bench.com/q/Vvl3-Pv2VMe12jOLtlEpbKfutCM

--
Sincerely,
Madhur Chauhan

“To live is the rarest thing in the world. Most people exist, that is all.”
- Oscar Wilde