[PATCH] Fix a comparison bug in diff-delta.c

[PATCH] Fix a comparison bug in diff-delta.c

[Pierre Habouzit]

(1 << i) < hspace is compared in the `int` space rather that in the unsigned one.
the result will be wrong if hspace is between  0x40000000 and 0x80000000.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
---

  I'm currently trying to make git compile with more strict gcc flags
(-g -O2 -Wall -Wextra -Wno-unused -Werror to be precise) and I've
spotted a first bug due to a signed/unsigned comparison.

  If I do understand that bit of code, it should not bite a lot of
people, but this is still a bug ;)


 diff-delta.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/diff-delta.c b/diff-delta.c
index 7da9205..a1fadc9 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -152,7 +152,7 @@ struct delta_index * create_delta_index(
 	   initialization in create_delta(). */
 	entries = (bufsize - 1)  / RABIN_WINDOW;
 	hsize = entries / 4;
-	for (i = 4; (1 << i) < hsize && i < 31; i++);
+	for (i = 4; (unsigned)(1 << i) < hsize && i < 31; i++);
 	hsize = 1 << i;
 	hmask = hsize - 1;
 
-- 
1.4.1.1

Re: [PATCH] Fix a comparison bug in diff-delta.c

[Pierre Habouzit]

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Le mer 23 août 2006 04:32, Pierre Habouzit a écrit :
>   I'm currently trying to make git compile with more strict gcc flags
> (-g -O2 -Wall -Wextra -Wno-unused -Werror to be precise) and I've
> spotted a first bug due to a signed/unsigned comparison.

still in the same kind of "problems" sha1_name.c:512 has:

		if (active_nr < 0)
			return -1;

but active_nr is defined as an unsigned (in cache.h/cache-read.c).

Also note that there is a *lot* of signed/unsigned comparisons due to 
the fact that it's unsigned, and that it's often compared to positions 
that are ints (I assume pos need the negative values to mean "error").

so either those two lines are too much, or active_nr has to be a plain 
signed int. I'm not used to git sources enough yet to be able to make 
the right decision.
-- 
·O·  Pierre Habouzit
··O                                                madcoder@debian.org
OOO                                                http://www.madism.org

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Re: [PATCH] Fix a comparison bug in diff-delta.c

[Nicolas Pitre]

On Wed, 23 Aug 2006, Pierre Habouzit wrote:

> (1 << i) < hspace is compared in the `int` space rather that in the unsigned one.
> the result will be wrong if hspace is between  0x40000000 and 0x80000000.
> 
> Signed-off-by: Pierre Habouzit <madcoder@debian.org>

Could you use (1u << i) instead of (unsigned)(1 << i) ?  That looks 
prettier to me at least.


Nicolas

[PATCH] Fix a comparison bug in diff-delta.c

[Pierre Habouzit]

  (1 << i) < hspace is compared in the `int` space rather that in the
  unsigned one.  the result will be wrong if hspace is between 0x40000000
  and 0x80000000.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
---

  This is a replacement for <1156300368160-git-send-email-madcoder@debian.org>
  avoiding the ugly cast, and using 1u instead.

 diff-delta.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/diff-delta.c b/diff-delta.c
index 7da9205..51e2e56 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -152,7 +152,7 @@ struct delta_index * create_delta_index(
 	   initialization in create_delta(). */
 	entries = (bufsize - 1)  / RABIN_WINDOW;
 	hsize = entries / 4;
-	for (i = 4; (1 << i) < hsize && i < 31; i++);
+	for (i = 4; (1u << i) < hsize && i < 31; i++);
 	hsize = 1 << i;
 	hmask = hsize - 1;
 
-- 
1.4.1.1

Re: [PATCH] Fix a comparison bug in diff-delta.c

[Johannes Schindelin]

Hi,

On Wed, 23 Aug 2006, Pierre Habouzit wrote:

> -	for (i = 4; (1 << i) < hsize && i < 31; i++);
> +	for (i = 4; (1u << i) < hsize && i < 31; i++);

The variable i never takes on the value 31 (or any higher value), so there 
is no bug here. Unless you port git to a system where an int has less than 
32 bit.

Ciao,
Dscho

Re: [PATCH] Fix a comparison bug in diff-delta.c

[Pierre Habouzit]

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Le mer 23 août 2006 15:45, Johannes Schindelin a écrit :
> Hi,
>
> On Wed, 23 Aug 2006, Pierre Habouzit wrote:
> > -	for (i = 4; (1 << i) < hsize && i < 31; i++);
> > +	for (i = 4; (1u << i) < hsize && i < 31; i++);
>
> The variable i never takes on the value 31 (or any higher value), so
> there is no bug here. Unless you port git to a system where an int
> has less than 32 bit.

that remains quite tasteless though, and maybe that patch can be 
integrated to the "cleanup" series I sent later today.
-- 
·O·  Pierre Habouzit
··O                                                madcoder@debian.org
OOO                                                http://www.madism.org

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