utf8.c

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/*
 * Copyright (C) 2022 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * 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 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 Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */
 
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
FILE_SECBOOT ( PERMITTED );
 
#include <stdint.h>
#include <assert.h>
#include <ipxe/utf8.h>
 
/** @file
 *
 * UTF-8 Unicode encoding
 *
 */
 
/**
 * Accumulate Unicode character from UTF-8 byte sequence
 *
 * @v utf8              UTF-8 accumulator
 * @v byte              UTF-8 byte
 * @ret character       Unicode character, or 0 if incomplete
 */
unsigned int utf8_accumulate ( struct utf8_accumulator *utf8, uint8_t byte ) {
        static unsigned int min[] = {
                UTF8_MIN_TWO,
                UTF8_MIN_THREE,
                UTF8_MIN_FOUR,
        };
        unsigned int shift;
        unsigned int len;
        uint8_t tmp;
 
        /* Handle continuation bytes */
        if ( UTF8_IS_CONTINUATION ( byte ) ) {
 
                /* Fail if this is an unexpected continuation byte */
                if ( utf8->remaining == 0 ) {
                        DBGC ( utf8, "UTF8 %p unexpected %02x\n", utf8, byte );
                        return UTF8_INVALID;
                }
 
                /* Apply continuation byte */
                utf8->character <<= UTF8_CONTINUATION_BITS;
                utf8->character |= ( byte & UTF8_CONTINUATION_MASK );
 
                /* Return 0 if more continuation bytes are expected */
                if ( --utf8->remaining != 0 )
                        return 0;
 
                /* Fail if sequence is illegal */
                if ( utf8->character < utf8->min ) {
                        DBGC ( utf8, "UTF8 %p illegal %02x\n", utf8,
                               utf8->character );
                        return UTF8_INVALID;
                }
 
                /* Sanity check */
                assert ( utf8->character != 0 );
 
                /* Return completed character */
                DBGC2 ( utf8, "UTF8 %p accumulated %02x\n",
                        utf8, utf8->character );
                return utf8->character;
        }
 
        /* Reset state and report failure if this is an unexpected
         * non-continuation byte.  Do not return UTF8_INVALID since
         * doing so could cause us to drop a valid ASCII character.
         */
        if ( utf8->remaining != 0 ) {
                shift = ( utf8->remaining * UTF8_CONTINUATION_BITS );
                DBGC ( utf8, "UTF8 %p unexpected %02x (partial %02x/%02x)\n",
                       utf8, byte, ( utf8->character << shift ),
                       ( ( 1 << shift ) - 1 ) );
                utf8->remaining = 0;
        }
 
        /* Handle initial bytes */
        if ( ! UTF8_IS_ASCII ( byte ) ) {
 
                /* Sanity check */
                assert ( utf8->remaining == 0 );
 
                /* Count total number of bytes in sequence */
                tmp = byte;
                len = 0;
                while ( tmp & UTF8_HIGH_BIT ) {
                        tmp <<= 1;
                        len++;
                }
 
                /* Check for illegal length */
                if ( len > UTF8_MAX_LEN ) {
                        DBGC ( utf8, "UTF8 %p illegal %02x length %d\n",
                               utf8, byte, len );
                        return UTF8_INVALID;
                }
 
                /* Store initial bits of character */
                utf8->character = ( tmp >> len );
 
                /* Store number of bytes remaining */
                len--;
                utf8->remaining = len;
                assert ( utf8->remaining > 0 );
 
                /* Store minimum legal value */
                utf8->min = min[ len - 1 ];
                assert ( utf8->min > 0 );
 
                /* Await continuation bytes */
                return 0;
        }
 
        /* Handle ASCII bytes */
        return byte;
}