libcruft-util/parse/value.cpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2017-2018 Danny Robson <danny@nerdcruft.net>
 */

#include "value.hpp"

#include "../cast.hpp"
#include <cruft/util/preprocessor.hpp>

#include <cstdlib>
#include <stdexcept>

using cruft::parse::value;

namespace {
    ///////////////////////////////////////////////////////////////////////////
    /// A trait class that records the C string parsing function for a given
    /// type.
    ///
    /// Not all types will necessarily have a corresponding parsing function.
    template <typename ValueT> struct parse_traits { };

    //-----------------------------------------------------------------------------
    template <> struct parse_traits<long>               { static constexpr auto value = strtol; };
    template <> struct parse_traits<long long>          { static constexpr auto value = strtoll; };
    template <> struct parse_traits<unsigned long>      { static constexpr auto value = strtoul; };
    template <> struct parse_traits<unsigned long long> { static constexpr auto value = strtoull; };


    //-----------------------------------------------------------------------------
    template <> struct parse_traits<float>       { static constexpr auto value = strtof; };
    template <> struct parse_traits<double>      { static constexpr auto value = strtod; };
    template <> struct parse_traits<long double> { static constexpr auto value = strtold; };


    ///////////////////////////////////////////////////////////////////////////
    template <
        typename ValueT,
        typename IteratorT,
        typename = std::enable_if_t<
            std::is_same_v<
                std::remove_cv_t<IteratorT>,
                char
            >
        >
    >
    ValueT
    c_iparse (cruft::view<IteratorT*> &data)
    {
        auto head = const_cast<char *> (data.begin ());
        auto tail = head;
        auto val  = parse_traits<ValueT>::value (head, &tail, 0);

        if (tail == head)
            throw std::invalid_argument ("unable to parse integer");

        data = data.consume (tail);
        return val;
    }


    //-------------------------------------------------------------------------
    template <
        typename ValueT,
        typename IteratorT,
        typename = std::enable_if_t<
            std::is_same_v<
                std::remove_cv_t<IteratorT>,
                char
            >
        >
    >
    ValueT
    c_fparse (cruft::view<IteratorT*> &data)
    {
        auto head = const_cast<char *> (data.begin ());
        auto tail = head;
        auto val  = parse_traits<ValueT>::value (head, &tail);

        if (tail == head)
            throw std::invalid_argument ("unable to parse float");

        data = data.consume (tail);
        return val;
    }
}


///////////////////////////////////////////////////////////////////////////////
/// Specialise cruft::parse for the type KLASS and dispatch the actual parsing
/// to safe template wrappers around the C parsing functions.
#define C_PARSE_ITERATOR(ITERATOR,PREFIX, KLASS)\
template <>                                     \
KLASS                                           \
cruft::parse::value<KLASS> (                    \
    cruft::view<ITERATOR> &str                  \
)  {                                            \
    return c_ ## PREFIX ## parse<KLASS> (str);  \
}

#define C_PARSE(PREFIX,KLASS) \
C_PARSE_ITERATOR(char *, PREFIX, KLASS) \
C_PARSE_ITERATOR(char const *, PREFIX, KLASS)


//-----------------------------------------------------------------------------
MAP1(C_PARSE, i,
    unsigned long,
    unsigned long long,
    long,
    long long
)


//-----------------------------------------------------------------------------
MAP1(C_PARSE, f,
    float,
    double,
    long double
)


///////////////////////////////////////////////////////////////////////////////
/// Specialise cruft::parse for the type FINAL and dispatch the actual parsing
/// to the safe template wrappers defined above, but use the type USED as an
/// intermediary type.
///
/// We need to parse using the type `USED` because there aren't C parsing
/// routines for all the fundamental types.
///
/// We check that the final result can safely fit within `FINAL` before
/// returning the value, else we raise an exception.
#define C_PARSE_WITH_CAST(FINAL, USED)                          \
template<>                                                      \
FINAL                                                           \
cruft::parse::value<FINAL> (cruft::view<char const*> &str) {    \
    auto remain = str;                                          \
    auto res = value<USED> (remain);                            \
    if (res > std::numeric_limits<FINAL>::max ())               \
        throw std::invalid_argument ("overflow during parse");  \
                                                                \
    str = remain;                                               \
    return cruft::cast::narrow<FINAL> (res);                    \
}


C_PARSE_WITH_CAST(short, long)
C_PARSE_WITH_CAST(int,   long)
C_PARSE_WITH_CAST(unsigned short, unsigned long)
C_PARSE_WITH_CAST(unsigned int,   unsigned long)