/* Copyright (c) 2020, 2024, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include <cstddef>
#include <cstdint>

namespace {
constexpr const int lookup_unhex_high[256] = {
    // 0x100 is an error flag
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0,     16,    32,    48,    64,    80,    96,
    112,   128,   144,   0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 160,
    176,   192,   208,   224,   240,   0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 160,   176,
    192,   208,   224,   240,   0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100};

constexpr const int lookup_unhex_low[256] = {
    // 0x100 is an error flag
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0,     1,     2,     3,     4,     5,     6,
    7,     8,     9,     0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 10,
    11,    12,    13,    14,    15,    0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 10,    11,
    12,    13,    14,    15,    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100, 0x100,
    0x100, 0x100, 0x100};
}  // namespace

bool unhex(const char *first, const char *last, char *output) {
  const std::ptrdiff_t length = last - first;

  if (length % 2) {
    const int hex_char = lookup_unhex_low[static_cast<unsigned char>(*first++)];
    if (hex_char > 255) return true;
    *output++ = static_cast<char>(hex_char);
  }

  for (const char *p = first; p != last; p += 2) {
    const int hex_char = lookup_unhex_high[static_cast<unsigned char>(p[0])] |
                         lookup_unhex_low[static_cast<unsigned char>(p[1])];
    if (hex_char > 255) return true;
    *output++ = static_cast<char>(hex_char);
  }

  return false;
}