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random: simplify add_ptr logic 

The add_ptr variable wasn't used in a sensible way, use only i instead.
i got reused later for a different purpose, use j instead.

While we're here, put tap0 first in the tap list and add a comment.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matt Mackall 2008-04-29 01:03:04 -07:00 committed by Linus Torvalds
parent 6d38b82740
commit 993ba2114c
1 changed files with 10 additions and 11 deletions
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21
drivers/char/random.c
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@ -454,7 +454,7 @@ static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
static __u32 const twist_table[8] = {
0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
unsigned long i, add_ptr, tap1, tap2, tap3, tap4, tap5;
unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
int input_rotate;
int wordmask = r->poolinfo->poolwords - 1;
__u32 w;
@ -469,19 +469,21 @@ static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
spin_lock_irqsave(&r->lock, flags);
input_rotate = r->input_rotate;
add_ptr = r->add_ptr;
i = r->add_ptr;
while (nwords--) {
w = rol32(*in++, input_rotate & 31);
i = add_ptr = (add_ptr - 1) & wordmask;
i = (i - 1) & wordmask;
/* XOR in the various taps */
w ^= r->pool[i];
w ^= r->pool[(i + tap1) & wordmask];
w ^= r->pool[(i + tap2) & wordmask];
w ^= r->pool[(i + tap3) & wordmask];
w ^= r->pool[(i + tap4) & wordmask];
w ^= r->pool[(i + tap5) & wordmask];
w ^= r->pool[i];
/* Mix the result back in with a twist */
r->pool[i] = (w >> 3) ^ twist_table[w & 7];
/*
@ -494,14 +496,11 @@ static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
}
r->input_rotate = input_rotate;
r->add_ptr = add_ptr;
r->add_ptr = i;
if (out) {
for (i = 0; i < 16; i++) {
out[i] = r->pool[add_ptr];
add_ptr = (add_ptr - 1) & wordmask;
}
}
if (out)
for (j = 0; j < 16; j++)
out[j] = r->pool[(i - j) & wordmask];
spin_unlock_irqrestore(&r->lock, flags);
}