Function count_digits

extlibs/fmt/include/fmt/format.h:787–792

Returns the number of decimal digits in n. Leading zeros are not counted except for n == 0 in which case count_digits returns 1.

// Returns the number of decimal digits in n. Leading zeros are not counted
// except for n == 0 in which case count_digits returns 1.
inline int count_digits(uint64_t n) {
  // Based on http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
  // and the benchmark https://github.com/localvoid/cxx-benchmark-count-digits.
  int t = (64 - FMT_BUILTIN_CLZLL(n | 1)) * 1233 >> 12;
  return t - (n < data::zero_or_powers_of_10_64[t]) + 1;
}
#else
// Fallback version of count_digits used when __builtin_clz is not available.
inline int count_digits(uint64_t n) {