Function parse_eight_digits_unrolled

app/src/ThirdParty/fast_float.h:1816–1825

credit @aqrit

// credit  @aqrit
fastfloat_really_inline FASTFLOAT_CONSTEXPR14 uint32_t
parse_eight_digits_unrolled(uint64_t val) {
  uint64_t const mask = 0x000000FF000000FF;
  uint64_t const mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
  uint64_t const mul2 = 0x0000271000000001; // 1 + (10000ULL << 32)
  val -= 0x3030303030303030;
  val = (val * 10) + (val >> 8); // val = (val * 2561) >> 8;
  val = (((val & mask) * mul1) + (((val >> 16) & mask) * mul2)) >> 32;
  return uint32_t(val);
}

// Call this if chars are definitely 8 digits.
template <typename UC>