From: Srujith Poojary <poojarysrujith@gmail.com>
Date: Sat, 24 Oct 2026 03:44:47 GMT
Subject: Re: [PATCH v2] diff-delta: use safe integer arithmetic
Message-ID: <CABh_KWj9wbanf6MSscwfurkgsaSgJvL_tg17sTt69TfWufnVyQ@mail.gmail.com>
In-Reply-To: <xmqq8q3o5k1q.fsf@gitster.g>

On Sat, Oct 24, 2026 at 12:19 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> Phillip Wood <phillip.wood123@gmail.com> writes:
>
> >> +    memsize = st_add3(sizeof(*index),
> >> +                    st_mult(sizeof(*packed_hash), hsize + 1),
> >
> > What are the bounds of hsize? Can adding one to it overflow? The
> > alignment is off here as well, all the arguments to st_add3() should be
> > aligned.
>
> Very good question, and I think hsize is capped at 1^26 in a code
> early in this function, which makes this safe.  It needs to be
> explained why it is safe in the log message, though.

Hi Junio,

Thank you for analyzing the struct alignment and memory allocation limits.
I have updated the commit message to explain why st_mult/st_add are
necessary on 32-bit platforms due to padding, as well as documenting
that hsize + 1 is safe because hsize is capped at 2^26.
I also fixed the code formatting using git clang-format HEAD^.

Best regards,
Srujith