utf8.cpp

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/*
All original material Copyright (C) 2002-2025 UFO: Alien Invasion.
 
Copyright (C) 1997-2001 Id Software, Inc.
 
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 (at your option) 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., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/
 
#include "utf8.h"
#include <string.h>

int UTF8_delete_char_at (char* s, int pos)
{
    /* Convert the UTF-8 char offset to byte offset */
    pos = UTF8_char_offset_to_byte_offset(s, pos);
 
    int start = pos;
    int next = pos;
 
    while (start > 0 && UTF8_CONTINUATION_BYTE(s[start]))
        start--;
    if (s[next] != 0)
        next++;
    while (s[next] != 0 && UTF8_CONTINUATION_BYTE(s[next]))
        next++;
    /* memmove is the only standard copying function that is guaranteed
     * to work if the source and destination overlap. */
    memmove(&s[start], &s[next], strlen(&s[next]) + 1);
    return (next - start);
}

int UTF8_insert_char_at (char* s, int n, int pos, int c)
{
    /* Convert the UTF-8 char offset to byte offset */
    pos = UTF8_char_offset_to_byte_offset(s, pos);
 
    const int utf8len = UTF8_encoded_len(c);
    const int tail = strlen(&s[pos]) + 1;
 
    if (utf8len == 0)
        return 0;
 
    if (pos + tail + utf8len > n)
        return 0;
 
    /* Insertion: move up rest of string. Also moves string terminator. */
    memmove(&s[pos + utf8len], &s[pos], tail);
 
    if (c <= 0x7f) {
        s[pos] = c;
    } else if (c <= 0x7ff) {                /* c has 11 bits */
        s[pos] = 0xc0 | (c >> 6);               /* high 5 bits */
        s[pos + 1] = 0x80 | (c & 0x3f);         /* low 6 bits */
    } else if (c <= 0xffff) {               /* c has 16 bits */
        s[pos] = 0xe0 | (c >> 12);              /* high 4 bits */
        s[pos + 1] = 0x80 | ((c >> 6) & 0x3f);  /* mid 6 bits */
        s[pos + 2] = 0x80 | (c & 0x3f);         /* low 6 bits */
    } else if (c <= 0x10ffff) {             /* c has 21 bits */
        s[pos] = 0xf0 | (c >> 18);              /* high 3 bits */
        s[pos + 1] = 0x80 | ((c >> 12) & 0x3f); /* mid 6 bits */
        s[pos + 2] = 0x80 | ((c >> 6) & 0x3f);  /* mid 6 bits */
        s[pos + 3] = 0x80 | (c & 0x3f);         /* low 6 bits */
    }
 
    return utf8len;
}

int UTF8_char_len (unsigned char c)
{
    if (c < 0x80)
        return 1;
    if (c < 0xc0)
        return 0;
    if (c < 0xe0)
        return 2;
    if (c < 0xf0)
        return 3;
    if (c < 0xf8)
        return 4;
    /* UTF-8 used to define 5 and 6 byte sequences, but they are
     * no longer valid. */
    return 0;
}

int UTF8_next (const char** str)
{
    size_t len, i;
    int cp, min;
    const char* s = *str;
 
    if (s[0] == '\0')
        return -1;
 
    const unsigned char* buf = (const unsigned char*)(s);
 
    if (buf[0] < 0x80) {
        len = 1;
        min = 0;
        cp = buf[0];
    } else if (buf[0] < 0xC0) {
        return -1;
    } else if (buf[0] < 0xE0) {
        len = 2;
        min = 1 << 7;
        cp = buf[0] & 0x1F;
    } else if (buf[0] < 0xF0) {
        len = 3;
        min = 1 << (5 + 6);
        cp = buf[0] & 0x0F;
    } else if (buf[0] < 0xF8) {
        len = 4;
        min = 1 << (4 + 6 + 6);
        cp = buf[0] & 0x07;
    } else {
        return -1;
    }
 
    for (i = 1; i < len; i++) {
        if (!UTF8_CONTINUATION_BYTE(buf[i]))
            return -1;
        cp = (cp << 6) | (buf[i] & 0x3F);
    }
 
    if (cp < min)
        return -1;
 
    if (0xD800 <= cp && cp <= 0xDFFF)
        return -1;
 
    if (0x110000 <= cp)
        return -1;
 
    *str += len;
    return cp;
}

int UTF8_encoded_len (int c)
{
    if (c <= 0x7F)
        return 1;
    if (c <= 0x07FF)
        return 2;
    if (c <= 0xFFFF)
        return 3;
    if (c <= 0x10FFFF)  /* highest defined Unicode code */
        return 4;
    return 0;
}

size_t UTF8_strlen (const char* str)
{
    size_t result = 0;
 
    while (str[0] != '\0') {
        const int n = UTF8_char_len((unsigned char)*str);
        str += n;
        result++;
    }
    return result;
}

int UTF8_char_offset_to_byte_offset (char* str, int pos)
{
    int result = 0;
 
    while (pos > 0 && str[0] != '\0') {
        const int n = UTF8_char_len((unsigned char)*str);
        str += n;
        result += n;
        pos--;
    }
    return result;
}

char* UTF8_strncpyz (char* dest, const char* src, size_t limit)
{
    size_t length;
 
    length = strlen(src);
    if (length > limit - 1) {
        length = limit - 1;
        if (length > 0 && (unsigned char) src[length - 1] >= 0x80) {
            size_t i = length - 1;
            while ((i > 0) && UTF8_CONTINUATION_BYTE((unsigned char) src[i]))
                i--;
            if (UTF8_char_len(src[i]) + i > length)
                length = i;
        }
    }
 
    memcpy(dest, src, length);
    dest[length] = '\0';
 
    return dest;
}