Permalink
Browse files

create_delta_index: simplify condition always evaluating to true

The code sequence  ' (1u << i) < hsize && i < 31 ' is a multi step
process, whose first step requires that 'i' is already less that 31,
otherwise the result (1u << i)  is undefined (and  'undef_val < hsize'
can therefore be assumed to be 'false'), and so the later test  i < 31
can always be optimized away as dead code ('i' is already less than 31,
or the short circuit 'and' applies).

So we need to get rid of that code. One way would be to exchange the
order of the conditions, so the expression 'i < 31 && (1u << i) < hsize'
would remove that optimized unstable code already.

However when checking the previous lines in that function, we can deduce
that 'hsize' must always be smaller than (1u<<31), since 506049c
(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 and we can remove that condition
entirely.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Acked-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
  • Loading branch information...
1 parent edca415 commit f7466e94375b3be27f229c78873f0acf8301c0a5 @stefanbeller stefanbeller committed with gitster Aug 16, 2013
Showing with 1 addition and 1 deletion.
  1. +1 −1 diff-delta.c
View
@@ -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;

0 comments on commit f7466e9

Please sign in to comment.