#include <string.h>
#include <stdlib.h>

char *dirname (char *path)
{
  static const char dot[] = ".";
  char *last_slash;
  /* Find last '/'.  */
  last_slash = path != NULL ? strrchr (path, '/') : NULL;
  if (last_slash != NULL && last_slash != path && last_slash[1] == '\0')
    {
      /* Determine whether all remaining characters are slashes.  */
      char *runp;
      for (runp = last_slash; runp != path; --runp)
        if (runp[-1] != '/')
          break;
      /* The '/' is the last character, we have to look further.  */
      if (runp != path)
        last_slash = memrchr (path, '/', runp - path);
    }
  if (last_slash != NULL)
    {
      /* Determine whether all remaining characters are slashes.  */
      char *runp;
      for (runp = last_slash; runp != path; --runp)
        if (runp[-1] != '/')
          break;
      /* Terminate the path.  */
      if (runp == path)
        {
          /* The last slash is the first character in the string.  We have to
             return "/".  As a special case we have to return "//" if there
             are exactly two slashes at the beginning of the string.  See
             XBD 4.10 Path Name Resolution for more information.  */
          if (last_slash == path + 1)
            ++last_slash;
          else
            last_slash = path + 1;
        }
      else
        last_slash = runp;
      last_slash[0] = '\0';
    }
  else
    /* This assignment is ill-designed but the XPG specs require to
       return a string containing "." in any case no directory part is
       found and so a static and constant string is required.  */
    path = (char *) dot;
  return path;
}