整理

2026-03-23 20:54:41 +08:00
commit e13b3650e9
4596 changed files with 1015768 additions and 0 deletions
--- a/include/boost/detail/lcast_precision.hpp
+++ b/include/boost/detail/lcast_precision.hpp
@@ -0,0 +1,83 @@
+// 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
+