fast_strlcpy

fast_strlcpy.c

/* Copyright (c) 1998, 2015 Todd C. Miller <millert@openbsd.org>
 *           (c) 2021 Andrii Makukha
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */


/*
 * @brief   Copy string src to buffer dst of size dsize. At most dsize-1 chars
 *          will be copied. Always NUL-terminates (unless dsize == 0).
 *
 * @return  dsize if truncation occured
 *          zero if dsize is zero
 *          othersize - length of string copied
 *
 * Based on https://github.com/libressl-portable/openbsd/blob/master/src/lib/libc/string/strlcpy.c
 */
size_t fast_strlcpy(char *dst, const char *src, size_t dsize)
{
    const char *osrc = src;
    size_t nleft = dsize;

    // Copy as many bytes as will fit.
    if (nleft != 0) {
        while (--nleft != 0) {
            if ((*dst++ = *src++) == '\0')
                break;
        }
    }

    // Not enough room in dst, add NUL.
    if (nleft == 0) {
        if (dsize != 0)
            *dst = '\0';            // NUL-terminate dst

        //while (*src++);           // Original strlcpy from OpenBSD - this is slow and unsafe
        src++;                      // Change in this "fast" version
    }

    // Count does not include NUL
    return (src - osrc - 1);
}