--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rand-dev-random.c	Thu Aug 03 10:22:07 2017 +0200
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2017 Guido Berhoerster <guido+pwm@berhoerster.name>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include "compat.h"
+
+#ifdef	HAVE_ERR_H
+#include <err.h>
+#endif /* HAVE_ERR_H */
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "rand.h"
+
+#ifdef	__linux__
+#define	PATH_DEV_RANDOM	"/dev/urandom"
+#else
+#define	PATH_DEV_RANDOM	"/dev/random"
+#endif /* __linux__ */
+
+void
+rand_buf(void *buf, size_t buf_size)
+{
+	unsigned char	*p = buf;
+	int		fd;
+	ssize_t		nread;
+	size_t		nsize = buf_size;
+
+	do {
+		fd = open(PATH_DEV_RANDOM, O_RDONLY);
+	} while ((fd < 0) && (errno == EINTR));
+	if (fd < 0) {
+		err(1, "open");
+	}
+
+	while (nsize > 0) {
+		nread = read(fd, p, nsize);
+		if (nread < 0) {
+			if (errno == EINTR) {
+				continue;
+			}
+			err(1, "read");
+		}
+		p += nread;
+		nsize -= nread;
+	}
+
+	while ((close(fd) < 0) && (errno == EINTR));
+}
+
+uint32_t
+rand_random(void)
+{
+	uint32_t	x;
+
+	rand_buf(&x, sizeof (x));
+
+	return (x);
+}
+
+/* random number between 0 and upper_bound - 1 without modulo bias */
+uint32_t
+rand_uniform(uint32_t upper_bound)
+{
+	uint32_t	r;
+	/* (2^32 - upper_bound) % upper_bound */
+	uint32_t	threshold = -upper_bound % upper_bound;
+
+	do {
+		r = rand_random();
+	} while (r < threshold);
+
+	return (r % upper_bound);
+}