text: /*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
  │vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
  ╞══════════════════════════════════════════════════════════════════════════════╡
  │ Copyright 2020 Justine Alexandra Roberts Tunney                              │
  │                                                                              │
  │ Permission to use, copy, modify, and/or 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.                                                │
  ╚─────────────────────────────────────────────────────────────────────────────*/
  #include "libc/fmt/conv.h"
  #include "libc/str/str.h"
  
  #define ISSLASH(c) (c == '/' || c == '\\')
  #define ISDELIM(c) (ISSLASH(c) || c == '.')
  
  /**
   * Returns directory portion of path.
   *
   * This returns "." if path doesn't have slashes. If path is empty then
   * this returns empty string.
   *
   * @param s is mutated and must not be NULL
   */
  char *dirname(char *s) {
    size_t i, n;
    if (!(n = strlen(s))) return s;
    while (n && ISDELIM(s[n - 1])) --n;
    if (n) {
      while (n && !ISSLASH(s[n - 1])) --n;
      if (n) {
        while (n && ISDELIM(s[n - 1])) --n;
        if (!n) ++n;
      } else {
        s[n++] = '.';
      }
    } else {
      ++n;
    }
    s[n] = '\0';
    return s;
  }
  