gp_seek.h

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// SPDX-License-Identifier: LGPL-2.1-or-later
/*
 
   Copyright (C) 2020-2024 Cyril Hrubis <metan@ucw.cz>
 
 */
 
#ifndef GP_SEEK_H
#define GP_SEEK_H
 
#include <sys/types.h>
#include <stddef.h>
 
enum gp_seek_whence {
        GP_SEEK_SET = 0,
        GP_SEEK_CUR = 1,
        GP_SEEK_END = 2,
};
 
static inline int gp_seek_off(ssize_t off, enum gp_seek_whence whence, size_t *cur_pos, size_t max_pos)
{
        switch (whence) {
        case GP_SEEK_SET:
                if (off < 0)
                        return -1;
 
                if ((size_t)off > max_pos)
                        return 1;
 
                *cur_pos = off;
 
                return 0;
        break;
        case GP_SEEK_CUR:
                if (off < 0) {
                        if (*cur_pos < (size_t)-off)
                                return -1;
                } else {
                        if (*cur_pos + (size_t)off > max_pos)
                                return 1;
                }
 
                *cur_pos += off;
 
                return 0;
        break;
        case GP_SEEK_END:
                if (off > 0)
                        return 1;
 
                if ((size_t)-off > max_pos)
                        return -1;
 
                *cur_pos = max_pos + off;
 
                return 0;
        break;
        }
 
        return -1;
}
 
#endif /* GP_SEEK_H */