mirror of
https://github.com/boostorg/lexical_cast.git
synced 2025-05-09 23:03:55 +00:00
84 lines
2.3 KiB
C++
84 lines
2.3 KiB
C++
// Copyright Alexander Nasonov & Paul A. Bristow 2006.
|
|
|
|
// Use, modification and distribution are subject to the
|
|
// Boost Software License, Version 1.0.
|
|
// (See accompanying file LICENSE_1_0.txt
|
|
// or copy at http://www.boost.org/LICENSE_1_0.txt)
|
|
|
|
#ifndef BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
|
|
#define BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
|
|
|
|
#include <climits>
|
|
#include <ios>
|
|
#include <limits>
|
|
|
|
#include <boost/config.hpp>
|
|
|
|
namespace boost { namespace detail {
|
|
|
|
// Calculate an argument to pass to std::ios_base::precision from
|
|
// lexical_cast.
|
|
template<class T>
|
|
struct lcast_precision
|
|
{
|
|
using limits = std::numeric_limits<T>;
|
|
|
|
static constexpr bool use_default_precision =
|
|
!limits::is_specialized || limits::is_exact
|
|
;
|
|
|
|
static constexpr bool is_specialized_bin =
|
|
!use_default_precision &&
|
|
limits::radix == 2 && limits::digits > 0
|
|
;
|
|
|
|
static constexpr bool is_specialized_dec =
|
|
!use_default_precision &&
|
|
limits::radix == 10 && limits::digits10 > 0
|
|
;
|
|
|
|
static constexpr std::streamsize streamsize_max =
|
|
(std::numeric_limits<std::streamsize>::max)()
|
|
;
|
|
|
|
static constexpr unsigned int precision_dec = limits::digits10 + 1U;
|
|
|
|
static_assert(!is_specialized_dec ||
|
|
precision_dec <= streamsize_max + 0UL
|
|
, "");
|
|
|
|
static constexpr unsigned long precision_bin =
|
|
2UL + limits::digits * 30103UL / 100000UL
|
|
;
|
|
|
|
static_assert(!is_specialized_bin ||
|
|
(limits::digits + 0UL < ULONG_MAX / 30103UL &&
|
|
precision_bin > limits::digits10 + 0UL &&
|
|
precision_bin <= streamsize_max + 0UL)
|
|
, "");
|
|
|
|
static constexpr std::streamsize value =
|
|
is_specialized_bin ? precision_bin
|
|
: is_specialized_dec ? precision_dec : 6
|
|
;
|
|
};
|
|
|
|
template<class T>
|
|
inline void lcast_set_precision(std::ios_base& stream, T*)
|
|
{
|
|
stream.precision(lcast_precision<T>::value);
|
|
}
|
|
|
|
template<class Source, class Target>
|
|
inline void lcast_set_precision(std::ios_base& stream, Source*, Target*)
|
|
{
|
|
std::streamsize const s = lcast_precision<Source>::value;
|
|
std::streamsize const t = lcast_precision<Target*>::value;
|
|
stream.precision(s > t ? s : t);
|
|
}
|
|
|
|
}}
|
|
|
|
#endif // BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED
|
|
|