Avoid 256 integer divisions per rc4_init() call. Replace it with using

separate index variable.

It gives more then double rc4_init() performance increase on tested i386 P4.
It also gives about 15% speedup to PPTP VPN with stateless MPPE encryption
(by ng_mppc) which calls rc4_init() for every packet.

1 files changed, 5 insertions, 3 deletions

diff --git a/sys/crypto/rc4/rc4.c b/sys/crypto/rc4/rc4.c
index f94a554..dbdbd7a 100644
--- a/sys/crypto/rc4/rc4.c
+++ b/sys/crypto/rc4/rc4.c
@@ -61,7 +61,7 @@ void
 rc4_init(struct rc4_state *const state, const u_char *key, int keylen)
 {
 	u_char j;
-	int i;
+	int i, k;
 
 	/* Initialize state with identity permutation */
 	for (i = 0; i < 256; i++)
@@ -70,9 +70,11 @@ rc4_init(struct rc4_state *const state, const u_char *key, int keylen)
 	state->index2 = 0;
   
 	/* Randomize the permutation using key data */
-	for (j = i = 0; i < 256; i++) {
-		j += state->perm[i] + key[i % keylen]; 
+	for (j = i = k = 0; i < 256; i++) {
+		j += state->perm[i] + key[k]; 
 		swap_bytes(&state->perm[i], &state->perm[j]);
+		if (++k >= keylen)
+			k = 0;
 	}
 }