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

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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.
This commit is contained in:
Alexander Motin 2008-12-16 13:58:37 +00:00
parent 848552f31f
commit f2831a952d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=186179
1 changed files with 5 additions and 3 deletions
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8
sys/crypto/rc4/rc4.c
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@ -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;
}
}