Improve seed() function

have_arc4random.c

@@ -0,0 +1,72 @@
+/*
+ * have_arc4random - Determine if we have the arc4random_buf() RNG
+ *
+ * Copyright (C) 2021  Landon Curt Noll
+ *
+ * Calc is open software; you can redistribute it and/or modify it under
+ * the terms of the version 2.1 of the GNU Lesser General Public License
+ * as published by the Free Software Foundation.
+ *
+ * Calc 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 Lesser General
+ * Public License for more details.
+ *
+ * A copy of version 2.1 of the GNU Lesser General Public License is
+ * distributed with calc under the filename COPYING-LGPL.  You should have
+ * received a copy with calc; if not, write to Free Software Foundation, Inc.
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * Under source code control:	2021/12/06 23:58:51
+ * File existed as early as:	2021
+ *
+ * chongo <was here> /\oo/\	http://www.isthe.com/chongo/
+ * Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
+ */
+
+/*
+ * usage:
+ *	have_arc4random
+ *
+ * Not all enviroments have the arc4random_buf() function,
+ * so this may not compile on your system.
+ *
+ * This prog outputs:
+ *
+ *	HAVE_ARC4RANDOM
+ *		defined ==> have arc4random_buf() call
+ *		undefined ==> do not have arc4random_buf() call
+ */
+
+#include "have_stdlib.h"
+#if defined(HAVE_STDLIB_H)
+#include <stdlib.h>
+#endif
+#include <stdio.h>
+
+
+#include "banned.h"	/* include after system header <> includes */
+
+
+#define BUFLEN (32)		/* length of the buffer to fill */
+
+
+int
+main(void)
+{
+#if defined(HAVE_NO_ARC4RANDOM)
+
+	printf("#undef HAVE_ARC4RANDOM /* no */\n");
+
+#else /* HAVE_NO_ARC4RANDOM */
+
+	static char buf[BUFLEN];	/* buffer for arc4random_buf() to fill */
+
+	arc4random_buf(buf, BUFLEN);
+	printf("#define HAVE_ARC4RANDOM /* yes */\n");
+
+#endif /* HAVE_NO_ARC4RANDOM */
+
+	/* exit(0); */
+	return 0;
+}