From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 15 Aug 2013 21:43:35 GMT
Subject: Re: [PATCH] create_delta_index: simplify condition always evaluating to true
Message-ID: <7vzjsipr3s.fsf@alter.siamese.dyndns.org>
In-Reply-To: <1376595460-6546-1-git-send-email-stefanbeller@googlemail.com>

Forwarding to the area expert...

Stefan Beller <stefanbeller@googlemail.com> writes:

> When checking the previous lines in that function, we can deduct that
> hsize must always be smaller than (1u<<31), since 506049c7df2c6
> (fix >4GiB source delta assertion failure), because the entries is
> capped at an upper bound of 0xfffffffeU, so hsize contains a maximum
> value of 0x3fffffff, which is smaller than (1u<<31), so i will never
> be larger than 31.
>
> Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
> ---
>  diff-delta.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/diff-delta.c b/diff-delta.c
> index 93385e1..54da95b 100644
> --- a/diff-delta.c
> +++ b/diff-delta.c
> @@ -154,8 +154,15 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
>  		 */
>  		entries = 0xfffffffeU / RABIN_WINDOW;
>  	}
> +
> +	/*
> +	 * Do not check i < 31 in the loop, because the assignement
> +	 * previous to the loop makes sure, hsize is definitely
> +	 * smaller than 1<<31, hence the loop will always stop
> +	 * before i exceeds 31 resulting in an infinite loop.
> +	 */
>  	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;