libcruft-util/cruft/util/encode/number.hpp

/*
 * 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 2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../view.hpp"
#include "../maths.hpp"

#include <array>
#include <limits>


///////////////////////////////////////////////////////////////////////////////
namespace cruft::encode {
    template <typename ValueT>
    ValueT
    decode36 (cruft::view<char const*> &src)
    {
        ValueT accum = 0;

        auto cursor = src.begin ();
        for (auto last = src.end (); cursor != last; ++cursor) {
            switch (auto i = *cursor; i) {
            case '0'...'9': accum = accum * 36 + i - '0';      continue;
            case 'a'...'z': accum = accum * 36 + i - 'a' + 10; continue;
            case 'A'...'Z': accum = accum * 36 + i - 'A' + 10; continue;
            }

            break;
        }

        src = { cursor, src.end () };
        return accum;
    }


    template <typename ValueT, typename OutputT>
    OutputT
    encode36 (OutputT out, ValueT val)
    {
        constexpr auto count = digits(std::numeric_limits<ValueT>::max (), 36u);
        std::array<char, count> res;

        auto cursor = res.begin ();
        // Ensure we do at least one iteration so we output a zero.
        do {
            switch (auto const d = val % 36; d) {
            case  0 ... 9: *cursor = d      + '0'; break;
            case 10 ...35: *cursor = d - 10 + 'a'; break;
            }

            val /= 36;
            ++cursor;
        } while (val);

        return std::copy (
            std::make_reverse_iterator (cursor),
            res.rend (),
            out
        );
    }
}