[src/trunk]: src/lib/libc/gen cache rs.i and rs.j in arc4random_buf() since t...

[dsl <dsl%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4694808316ea
branches:  trunk
changeset: 781097:4694808316ea
user:      dsl <dsl%NetBSD.org@localhost>
date:      Sat Aug 18 15:55:07 2012 +0000

description:
cache rs.i and rs.j in arc4random_buf() since the compiler can't be
  told that buf[] dosn't alias them.
Reduces the number of instructions inside the loop.
All the other functions are ok.

diffstat:

 lib/libc/gen/arc4random.c |  40 +++++++++++++++++++++++++++-------------
 1 files changed, 27 insertions(+), 13 deletions(-)

diffs (82 lines):

diff -r 60e4b35d2d13 -r 4694808316ea lib/libc/gen/arc4random.c
--- a/lib/libc/gen/arc4random.c Sat Aug 18 15:25:15 2012 +0000
+++ b/lib/libc/gen/arc4random.c Sat Aug 18 15:55:07 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: arc4random.c,v 1.16 2012/08/18 15:04:53 dsl Exp $      */
+/*     $NetBSD: arc4random.c,v 1.17 2012/08/18 15:55:07 dsl Exp $      */
 /*     $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $ */
 
 /*
@@ -27,7 +27,7 @@
 
 #include <sys/cdefs.h>
 #if defined(LIBC_SCCS) && !defined(lint)
-__RCSID("$NetBSD: arc4random.c,v 1.16 2012/08/18 15:04:53 dsl Exp $");
+__RCSID("$NetBSD: arc4random.c,v 1.17 2012/08/18 15:55:07 dsl Exp $");
 #endif /* LIBC_SCCS and not lint */
 
 #include "namespace.h"
@@ -150,20 +150,26 @@
                arc4_getbyte(as);
 }
 
-static inline uint8_t
-arc4_getbyte(struct arc4_stream *as)
+static __always_inline uint8_t
+arc4_getbyte_ij(struct arc4_stream *as, uint8_t *i, uint8_t *j)
 {
        uint8_t si, sj;
 
-       as->i = (as->i + 1);
-       si = as->s[as->i];
-       as->j = (as->j + si);
-       sj = as->s[as->j];
-       as->s[as->i] = sj;
-       as->s[as->j] = si;
+       *i = *i + 1;
+       si = as->s[*i];
+       *j = *j + si;
+       sj = as->s[*j];
+       as->s[*i] = sj;
+       as->s[*j] = si;
        return (as->s[(si + sj) & 0xff]);
 }
 
+static inline uint8_t
+arc4_getbyte(struct arc4_stream *as)
+{
+       return arc4_getbyte_ij(as, &as->i, &as->j);
+}
+
 static inline uint32_t
 arc4_getword(struct arc4_stream *as)
 {
@@ -210,17 +216,25 @@
 {
        uint8_t *bp = buf;
        uint8_t *ep = bp + len;
+       uint8_t i, j;
        int skip;
 
        LOCK(&rs);
        arc4_check_init(&rs);
 
-       skip = arc4_getbyte(&rs) % 3;
+       /* cache i and j - compiler can't know 'buf' doesn't alias them */
+       i = rs.i;
+       j = rs.j;
+
+       skip = arc4_getbyte_ij(&rs, &i, &j) % 3;
        while (skip--)
-               (void)arc4_getbyte(&rs);
+               (void)arc4_getbyte_ij(&rs, &i, &j);
 
        while (bp < ep)
-               *bp++ = arc4_getbyte(&rs);
+               *bp++ = arc4_getbyte_ij(&rs, &i, &j);
+       rs.i = i;
+       rs.j = j;
+
        UNLOCK(&rs);
 }