From: "Stefan Beller" <stefanbeller@xxxxxxxxxxxxxx>
When checking the previous lines in that function, we can deduce that
hsize must always be smaller than (1u<<31), since 506049c7df2c6
(fix >4GiB source delta assertion failure), because entries is
capped at an upper bound of 0xfffffffeU, so hsize contains a maximum
value of 0x3fffffff, which is smaller than (1u<<31), so the value of
'i' will never be larger than 31.
Signed-off-by: Stefan Beller <stefanbeller@xxxxxxxxxxxxxx>
---
Eric, thanks for reviewing my patch.
I applied the first 2 proposals (deduce, entries), but I disagree on
the third, so I reformulated the sentence, as I really meant the
variable
i and not it as a pronoun.
Do I understand right, you're suggesting to remove the
source code comment? I did this now, but I have a bad feeling with it.
The change of this patch surely removes dead code as of now and makes
it
more readable. But also it could become alive again, once somebody
changes things nearby and forgets about the assumption, hsize not
exceeding a certain size. That's why I put a comment in there, so
the future changes nearby may be more careful.
Should the comment also include a note about potential undefined
behaviour of a large shift, with the possible consequential bad compiler
optimization, such as simply deleting the code. I understand the initial
spot was part of the STACK tool check of such latent optimisation bugs.
http://css.csail.mit.edu/stack/
Thanks,
Stefan
diff-delta.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/diff-delta.c b/diff-delta.c
index 93385e1..3797ce6 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -155,7 +155,7 @@ struct delta_index * create_delta_index(const void
*buf, unsigned long bufsize)
entries = 0xfffffffeU / RABIN_WINDOW;
}
hsize = entries / 4;
- for (i = 4; (1u << i) < hsize && i < 31; i++);
+ for (i = 4; (1u << i) < hsize; i++);
hsize = 1 << i;
hmask = hsize - 1;
--
1.8.4.rc3.1.gc1ebd90
--
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