No point in refreshing the pid from inside arc4_stir() when that

doesn't test it, so factor out the two places that test it into a
routine and do the refreshing there.  With this, arch4random_buf()
doesn't trigger superfluous calls to getpid() when filling large
buffers.
ok deraadt@, "looks nicer indeed" otto@

src/lib/libc/crypt/arc4random.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: arc4random.c,v 1.20 2008/10/03 18:46:04 otto Exp $	*/
+/*	$OpenBSD: arc4random.c,v 1.21 2009/12/15 18:19:06 guenther Exp $	*/
 
 /*
  * Copyright (c) 1996, David Mazieres <dm@uun.org>
@@ -109,7 +109,6 @@ arc4_stir(void)
 	len = sizeof(rnd);
 	sysctl(mib, 2, rnd, &len, NULL, 0);
 
-	arc4_stir_pid = getpid();
 	arc4_addrandom(rnd, sizeof(rnd));
 
 	/*
@@ -121,6 +120,18 @@ arc4_stir(void)
 	arc4_count = 1600000;
 }
 
+static void
+arc4_stir_if_needed(void)
+{
+	pid_t pid = getpid();
+
+	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
+	{
+		arc4_stir_pid = pid;
+		arc4_stir();
+	}
+}
+
 static inline u_int8_t
 arc4_getbyte(void)
 {
@@ -170,8 +181,7 @@ arc4random(void)
 	u_int32_t val;
 	_ARC4_LOCK();
 	arc4_count -= 4;
-	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid())
-		arc4_stir();
+	arc4_stir_if_needed();
 	val = arc4_getword();
 	_ARC4_UNLOCK();
 	return val;
@@ -182,8 +192,7 @@ arc4random_buf(void *_buf, size_t n)
 {
 	u_char *buf = (u_char *)_buf;
 	_ARC4_LOCK();
-	if (!rs_initialized || arc4_stir_pid != getpid())
-		arc4_stir();
+	arc4_stir_if_needed();
 	while (n--) {
 		if (--arc4_count <= 0)
 			arc4_stir();