TextSupport.h

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// Copyright © 2008-2023 Pioneer Developers. See AUTHORS.txt for details
// Licensed under the terms of the GPL v3. See licenses/GPL-3.txt
 
#ifndef _TEXT_TEXTSUPPORT_H
#define _TEXT_TEXTSUPPORT_H
 
#include <SDL_stdinc.h>
#include <cassert>
 
namespace Text {
 
    // various text-related functions. a proper home needs to be found for them.
 
    // convert one multibyte (utf8) char to a widechar (utf32/ucs4)
    //  chr: pointer to output storage
    //  src: multibyte string
    //  returns: number of bytes swallowed, or 0 if end of string
    int utf8_decode_char(Uint32 *chr, const char *src);
 
    // encode one Unicode code-point as UTF-8
    //  chr: the Unicode code-point
    //  buf: a character buffer, which must have space for at least 4 bytes
    //       (i.e., assigning to buf[3] must be a valid operation)
    //  returns: number of bytes in the encoded character
    int utf8_encode_char(Uint32 chr, char buf[4]);
 
    // this can tell you the length of a UTF-8 character, or more generally
    // it tells you the number of bytes to move forward to get to the beginning
    // of the next character
    inline int utf8_next_char_offset(const char *str)
    {
        assert(str);
        assert(*str);
        const char *const start = str;
        if (*str & 0x80) {
            // technically, the first byte of a UTF-8 multi-byte sequence is enough
            // to determine the length of the sequence, but a loop is simpler and
            // more robust to incorrectly encoded text
            do {
                ++str;
            } while ((*str & 0xC0) == 0x80);
            return (str - start);
        } else
            return 1;
    }
 
    // this tells you the number of bytes to move backwards to get to the
    // beginning of the previous character (or the current character if you start inside a multi-byte sequence)
    // ('begin' indicates the start of the array and is used to avoid walking off the front)
    inline int utf8_prev_char_offset(const char *str, const char *const begin)
    {
        assert(str);
        assert(str > begin);
        const char *const start = str;
        --str;
        if (*str & 0x80) {
            while ((str > begin) && ((*str & 0xC0) == 0x80)) {
                --str;
            }
            return (start - str);
        } else
            return 1;
    }
 
    // returns true if the char c is an ASCII letter, a digit
    // or an underscore.
    inline bool is_alphanumunderscore(char c)
    {
        return (c == '_' || (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'));
    }
 
} // namespace Text
 
#endif