utf8.h

/*-
 * SPDX-License-Identifier: MIT
 *
 * Copyright (c) 2008-2010 Björn Höhrmann <bjoern@hoehrmann.de>
 * See http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#ifndef UTF8_H_
#define UTF8_H_

#include <stdint.h>

#define UTF8_ACCEPT 0
#define UTF8_REJECT 12

static const uint8_t utf8d[] = {
    // The first part of the table maps bytes to character classes that
    // to reduce the size of the transition table and create bitmasks.
     0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
     0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
     0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
     0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
     1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,  9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
     7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
     8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,  2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    10,3,3,3,3,3,3,3,3,3,3,3,3,4,3,3, 11,6,6,6,5,8,8,8,8,8,8,8,8,8,8,8,

    // The second part is a transition table that maps a combination
    // of a state of the automaton and a character class to a state.
     0,12,24,36,60,96,84,12,12,12,48,72, 12,12,12,12,12,12,12,12,12,12,12,12,
    12, 0,12,12,12,12,12, 0,12, 0,12,12, 12,24,12,12,12,12,12,24,12,24,12,12,
    12,12,12,12,12,12,12,24,12,12,12,12, 12,24,12,12,12,12,12,12,12,24,12,12,
    12,12,12,12,12,12,12,36,12,36,12,12, 12,36,12,12,12,12,12,36,12,36,12,12,
    12,36,12,12,12,12,12,12,12,12,12,12,
};

/*
 * This function implements a *single* step in decoding a UTF-8 character.
 * Except the byte parameter that accepts the byte to decode, it takes two
 * parameters maintaining the state, and returns the state achieved after
 * processing the byte.
 *
 * Return values:
 * - UTF8_ACCEPT: enough bytes have been read for a character
 * - UTF8_REJECT: the byte is not allowed to occur at its position
 * - other positive value: more bytes have to be read
 *
 * When decoding the first byte of a string, the caller must set $state =
 * UTF8_ACCEPT.  If, after decoding one or more bytes the state UTF8_ACCEPT
 * is reached again, then the decoded Unicode character value is available
 * through the $codep parameter.  If the state UTF8_REJECT is entered, that
 * state will never be exited unless the caller intervenes.
 */
static inline uint32_t
utf8_decode(uint32_t *state, uint32_t *codep, uint32_t byte)
{
    uint32_t type = utf8d[byte];

    *codep = (*state != UTF8_ACCEPT) ?
             (byte & 0x3fu) | (*codep << 6) :
             (0xff >> type) & (byte);

    *state = utf8d[256 + *state + type];
    return *state;
}

#endif