base_convert.h

// Copyright 2009-2018 Toby Schneider (http://gobysoft.org/index.wt/people/toby)
//                     GobySoft, LLC (2013-)
//                     Massachusetts Institute of Technology (2007-2014)
//                     Community contributors (see AUTHORS file)
//
//
// This file is part of the Goby Underwater Autonomy Project Libraries
// ("The Goby Libraries").
//
// The Goby Libraries are free software: you can redistribute them and/or modify
// them under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2.1 of the License, or
// (at your option) any later version.
//
// The Goby Libraries are distributed in the hope that they will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with Goby.  If not, see <http://www.gnu.org/licenses/>.

#include <gmp.h>

#include <string>

namespace goby
{
namespace util
{
inline void base_convert(const std::string& source, std::string* sink, int source_base,
                         int sink_base)
{
    mpz_t base10;
    mpz_init(base10);

    // record number of most significant zeros, e.g. 0023 has two
    int ms_zeros = 0;
    // false until a non-zero byte is encountered
    bool non_zero_byte = false;

    for (int i = source.size() - 1; i >= 0; --i)
    {
        int byte = 0xFF & source[i];
        mpz_add_ui(base10, base10, byte);
        if (i)
            mpz_mul_ui(base10, base10, source_base);

        if (byte == 0 && !non_zero_byte)
            ++ms_zeros;
        else
            non_zero_byte = true;
    }
    sink->clear();

    while (mpz_cmp_ui(base10, 0) != 0)
    {
        unsigned long int remainder = mpz_fdiv_q_ui(base10, base10, sink_base);
        sink->push_back(0xFF & remainder);
    }

    // preserve MS zeros by adding that number to the most significant end
    for (int i = 0; i < ms_zeros; ++i) sink->push_back(0);

    mpz_clear(base10);
}
} // namespace util
} // namespace goby