mktemp.c

/*	A part of the Windows CE C Extra Library (celibc)
	Copyright 2007-2015 PC GO Ld.

	This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

	This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
*/

#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/stat.h>

static const char letters[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

char *mktemp(char *template) {
	static uint64_t value;

	size_t len = strlen(template);
	char *p = template + len - 6;
	if(len < 6 || strcmp(p, "XXXXXX")) {
		errno = EINVAL;
		goto failed;
	}

	struct timeval tv;
	gettimeofday(&tv, NULL);
	uint64_t random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
	value += random_time_bits ^ getpid();
	unsigned int i;
	for(i=0; i<62*62*62; value+=7777, i++) {
		uint64_t v = value;
		/* Fill in the random bits.  */
		p[0] = letters[v % 62];
		v /= 62;
		p[1] = letters[v % 62];
		v /= 62;
		p[2] = letters[v % 62];
		v /= 62;
		p[3] = letters[v % 62];
		v /= 62;
		p[4] = letters[v % 62];
		v /= 62;
		p[5] = letters[v % 62];

		struct stat st;
		if(stat(template, &st) < 0) {
			if(errno == ENOENT) return template;
			goto failed;
		}
	}

	errno = EEXIST;
failed:
	*template = 0;
	return template;
}