json-validator/include/jvalidate/detail/number.h

/**
 * Utility functions for managing numeric types - such as converting between
 * floating-point and integer types.
 *
 * None of these are particularly complex functions, but storing them in a
 * single header with descriptive names helps the reader quickly recognize what
 * is being done.
 */
#pragma once

#include <charconv>
#include <cmath>
#include <limits>
#include <stdexcept>
#include <string_view>
#include <system_error>

namespace jvalidate::detail {
/**
 * @brief Determine if a floating point number is actually an integer (in the
 * mathematical sense).
 */
inline bool is_json_integer(double number) { return std::floor(number) == number; }

/**
 * @brief Determine if a floating point number is actually an integer, and
 * actually fits in the 64-bit integer type that we use for JSON Integer.
 */
inline bool fits_in_integer(double number) {
  static constexpr double g_int_max = std::numeric_limits<int64_t>::max();
  static constexpr double g_int_min = std::numeric_limits<int64_t>::min();
  return is_json_integer(number) && number <= g_int_max && number >= g_int_min;
}

/**
 * @brief Determine if an unsigned integer fits into a signed integer
 */
inline bool fits_in_integer(uint64_t number) { return (number & 0x8000'0000'0000'0000) == 0; }

template <std::integral I> I from_str(std::string_view str, int base = 10) {
  I rval;
  auto [end, ec] = std::from_chars(str.begin(), str.end(), rval, base);

  if (ec != std::errc{}) {
    throw std::runtime_error(std::make_error_code(ec).message());
  }

  if (end != str.end()) {
    throw std::runtime_error("NaN: " + std::string(str));
  }

  return rval;
}
}