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include/boost/lexical_cast/detail/converter_numeric.hpp

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+// Copyright Kevlin Henney, 2000-2005.
+// Copyright Alexander Nasonov, 2006-2010.
+// Copyright Antony Polukhin, 2011-2025.
+//
+// Distributed under 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)
+//
+// what:  lexical_cast custom keyword cast
+// who:   contributed by Kevlin Henney,
+//        enhanced with contributions from Terje Slettebo,
+//        with additional fixes and suggestions from Gennaro Prota,
+//        Beman Dawes, Dave Abrahams, Daryle Walker, Peter Dimov,
+//        Alexander Nasonov, Antony Polukhin, Justin Viiret, Michael Hofmann,
+//        Cheng Yang, Matthew Bradbury, David W. Birdsall, Pavel Korzh and other Boosters
+// when:  November 2000, March 2003, June 2005, June 2006, March 2011 - 2016
+
+#ifndef BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
+#define BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
+
+#include <boost/config.hpp>
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#   pragma once
+#endif
+
+#include <type_traits>
+#include <boost/core/cmath.hpp>
+#include <boost/limits.hpp>
+#include <boost/lexical_cast/detail/type_traits.hpp>
+
+namespace boost { namespace detail {
+
+template <class Source, class Target>
+bool ios_numeric_comparer_float(Source x, Source y) noexcept {
+    return x == y
+        || (boost::core::isnan(x) && boost::core::isnan(y))
+        || (x < (std::numeric_limits<Target>::min)())
+    ;
+}
+
+template <class RangeType, class T>
+constexpr bool is_out_of_range_for(T value) noexcept {
+    return value > static_cast<T>((std::numeric_limits<RangeType>::max)())
+        || value < static_cast<T>((std::numeric_limits<RangeType>::min)())
+        || boost::core::isnan(value);
+}
+
+
+// integral -> integral
+template <typename Target, typename Source>
+typename std::enable_if<
+    !std::is_floating_point<Source>::value && !std::is_floating_point<Target>::value, bool
+>::type noexcept_numeric_convert(Source arg, Target& result) noexcept {
+    const Target target_tmp = static_cast<Target>(arg);
+    const Source arg_restored = static_cast<Source>(target_tmp);
+    if (arg == arg_restored) {
+        result = target_tmp;
+        return true;
+    }
+    return false;
+}
+
+// integral -> floating point
+template <typename Target, typename Source>
+typename std::enable_if<
+    !std::is_floating_point<Source>::value && std::is_floating_point<Target>::value, bool
+>::type noexcept_numeric_convert(Source arg, Target& result) noexcept {
+    const Target target_tmp = static_cast<Target>(arg);
+    result = target_tmp;
+    return true;
+}
+
+
+// floating point -> floating point
+template <typename Target, typename Source>
+typename std::enable_if<
+    std::is_floating_point<Source>::value && std::is_floating_point<Target>::value, bool
+>::type noexcept_numeric_convert(Source arg, Target& result) noexcept {
+    const Target target_tmp = static_cast<Target>(arg);
+    const Source arg_restored = static_cast<Source>(target_tmp);
+    if (detail::ios_numeric_comparer_float<Source, Target>(arg, arg_restored)) {
+        result = target_tmp;
+        return true;
+    }
+
+    return false;
+}
+
+// floating point -> integral
+template <typename Target, typename Source>
+typename std::enable_if<
+    std::is_floating_point<Source>::value && !std::is_floating_point<Target>::value, bool
+>::type noexcept_numeric_convert(Source arg, Target& result) noexcept {
+    if (detail::is_out_of_range_for<Target>(arg)) {
+        return false;
+    }
+
+    const Target target_tmp = static_cast<Target>(arg);
+    const Source arg_restored = static_cast<Source>(target_tmp);
+    if (arg == arg_restored /* special values are handled in detail::is_out_of_range_for */) {
+        result = target_tmp;
+        return true;
+    }
+
+    return false;
+}
+
+struct lexical_cast_dynamic_num_not_ignoring_minus
+{
+    template <typename Target, typename Source>
+    static inline bool try_convert(Source arg, Target& result) noexcept {
+        return boost::detail::noexcept_numeric_convert<Target, Source >(arg, result);
+    }
+};
+
+struct lexical_cast_dynamic_num_ignoring_minus
+{
+    template <typename Target, typename Source>
+#if defined(__clang__) && (__clang_major__ > 3 || __clang_minor__ > 6)
+    __attribute__((no_sanitize("unsigned-integer-overflow")))
+#endif
+    static inline bool try_convert(Source arg, Target& result) noexcept {
+        typedef typename std::conditional<
+                std::is_floating_point<Source>::value,
+                std::conditional<true, Source, Source>,  // std::type_identity emulation
+                boost::detail::lcast::make_unsigned<Source>
+        >::type usource_lazy_t;
+        typedef typename usource_lazy_t::type usource_t;
+
+        if (arg < 0) {
+            const bool res = boost::detail::noexcept_numeric_convert<Target, usource_t>(
+                static_cast<usource_t>(0u - static_cast<usource_t>(arg)), result
+            );
+            result = static_cast<Target>(0u - result);
+            return res;
+        } else {
+            return boost::detail::noexcept_numeric_convert<Target, usource_t>(arg, result);
+        }
+    }
+};
+
+/*
+ * dynamic_num_converter_impl follows the rules:
+ * 1) If Source can be converted to Target without precision loss and
+ * without overflows, then assign Source to Target and return
+ *
+ * 2) If Source is less than 0 and Target is an unsigned integer,
+ * then negate Source, check the requirements of rule 1) and if
+ * successful, assign static_casted Source to Target and return
+ *
+ * 3) Otherwise throw a bad_lexical_cast exception
+ *
+ *
+ * Rule 2) required because boost::lexical_cast has the behavior of
+ * stringstream, which uses the rules of scanf for conversions. And
+ * in the C99 standard for unsigned input value minus sign is
+ * optional, so if a negative number is read, no errors will arise
+ * and the result will be the two's complement.
+ */
+template <typename Target, typename Source>
+struct dynamic_num_converter_impl
+{
+    static inline bool try_convert(Source arg, Target& result) noexcept {
+        typedef typename std::conditional<
+            boost::detail::lcast::is_unsigned<Target>::value &&
+            (boost::detail::lcast::is_signed<Source>::value || std::is_floating_point<Source>::value) &&
+            !(std::is_same<Source, bool>::value) &&
+            !(std::is_same<Target, bool>::value),
+            lexical_cast_dynamic_num_ignoring_minus,
+            lexical_cast_dynamic_num_not_ignoring_minus
+        >::type caster_type;
+
+        return caster_type::try_convert(arg, result);
+    }
+};
+
+}} // namespace boost::detail
+
+#endif // BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
+