hdr_int_test.cc

#include <chrono>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <iostream>
#include <vector>

#include "date.h" // From https://github.com/HowardHinnant/date/blob/master/include/date/date.h

static constexpr const size_t magnitude_bits = 4;

union VariablePrecision {
  struct {
    uint16_t precision : 16 - magnitude_bits;
    uint16_t magnitude : magnitude_bits;
  } fields;
  uint16_t raw;
};

std::chrono::microseconds decode(VariablePrecision p) {
    auto count = uint64_t(1 + p.fields.precision) << uint64_t(p.fields.magnitude);
    return std::chrono::microseconds(count);
}

int main() {
    auto min = std::chrono::microseconds::max();
    auto max = std::chrono::microseconds::min();

    std::vector<std::chrono::microseconds> vec;
  for (uint16_t i = std::numeric_limits<uint16_t>::min();
       i < std::numeric_limits<uint16_t>::max();
       ++i) {
     VariablePrecision p;
     p.raw = i;
     auto decoded = decode(p);
     vec.emplace_back(decoded);
     if (decoded < min) {
       min = decoded;
     }
     if (decoded > max) {
       max = decoded;
     }
  }
  std::sort(vec.begin(), vec.end());
  for (const auto& v : vec) {
      std::cout << date::make_time(v) << "\n";
  }
  std::cout << "min:" << date::make_time(min) << " max:" << date::make_time(max) << "\n";
}

With 4 magnitude bits gives range of 1 microsecond to 2m14s:

min:00:00:00.000001 max:00:02:14.184960

With 5 magnitude bits, max increases to 1221 hours (50+ days), which is probably a bigger range than necessary:

min:00:00:00.000001 max:1221:04:59.027456