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From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>,
	git@vger.kernel.org,
	"Johannes Schindelin" <johannes.schindelin@gmx.de>,
	"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
Subject: Re: [PATCH 2/3] untracked-cache: simplify parsing by dropping "next"
Date: Fri, 19 Apr 2019 14:33:17 +0900	[thread overview]
Message-ID: <xmqq5zraeezm.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20190418211738.GB18520@sigill.intra.peff.net> (Jeff King's message of "Thu, 18 Apr 2019 17:17:38 -0400")

Jeff King <peff@peff.net> writes:

> When we parse an on-disk untracked cache, we have two pointers, "data"
> and "next". As we parse, we point "next" to the end of an element, and
> then later update "data" to match.
>
> But we actually don't need two pointers. Each parsing step can just
> update "data" directly from other variables we hold (and we don't have
> to worry about bailing in an intermediate state, since any parsing
> failure causes us to immediately discard "data" and return).

;-)  

My first reaction was "you can do so now you have introduced
eos--why didn't you do that in the previous step?", but losing
'next' from the varint parsing step would certainly have been
possible even before that change.  So I agree that it makes much
more sense to do this step separately from the previous one.

The code after the patch certainly reads easier and simpler.

Thanks.

> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  dir.c | 20 +++++++-------------
>  1 file changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/dir.c b/dir.c
> index 7b0513c476..17865f44df 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -2732,50 +2732,44 @@ static int read_one_dir(struct untracked_cache_dir **untracked_,
>  			struct read_data *rd)
>  {
>  	struct untracked_cache_dir ud, *untracked;
> -	const unsigned char *next, *data = rd->data, *end = rd->end;
> +	const unsigned char *data = rd->data, *end = rd->end;
>  	const unsigned char *eos;
>  	unsigned int value;
>  	int i, len;
>  
>  	memset(&ud, 0, sizeof(ud));
>  
> -	next = data;
> -	value = decode_varint(&next);
> -	if (next > end)
> +	value = decode_varint(&data);
> +	if (data > end)
>  		return -1;
>  	ud.recurse	   = 1;
>  	ud.untracked_alloc = value;
>  	ud.untracked_nr	   = value;
>  	if (ud.untracked_nr)
>  		ALLOC_ARRAY(ud.untracked, ud.untracked_nr);
> -	data = next;
>  
> -	next = data;
> -	ud.dirs_alloc = ud.dirs_nr = decode_varint(&next);
> -	if (next > end)
> +	ud.dirs_alloc = ud.dirs_nr = decode_varint(&data);
> +	if (data > end)
>  		return -1;
>  	ALLOC_ARRAY(ud.dirs, ud.dirs_nr);
> -	data = next;
>  
>  	eos = memchr(data, '\0', end - data);
>  	if (!eos || eos == end)
>  		return -1;
>  	len = eos - data;
> -	next = eos + 1;
>  
>  	*untracked_ = untracked = xmalloc(st_add3(sizeof(*untracked), len, 1));
>  	memcpy(untracked, &ud, sizeof(ud));
>  	memcpy(untracked->name, data, len + 1);
> -	data = next;
> +	data = eos + 1;
>  
>  	for (i = 0; i < untracked->untracked_nr; i++) {
>  		eos = memchr(data, '\0', end - data);
>  		if (!eos || eos == end)
>  			return -1;
>  		len = eos - data;
> -		next = eos + 1;
>  		untracked->untracked[i] = xmemdupz(data, len);
> -		data = next;
> +		data = eos + 1;
>  	}
>  
>  	rd->ucd[rd->index++] = untracked;

  reply	other threads:[~2019-04-19 18:37 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-10 12:56 [PATCH 0/1] Fix an off-by-one bug in the untracked cache code Johannes Schindelin via GitGitGadget
2019-04-10 12:56 ` [PATCH 1/1] untracked cache: fix off-by-one Johannes Schindelin via GitGitGadget
2019-04-10 16:20   ` Jeff King
2019-04-12  1:48     ` Junio C Hamano
2019-04-18 21:14       ` [PATCH 0/3] untracked cache parsing fixups Jeff King
2019-04-18 21:17         ` [PATCH 1/3] untracked-cache: be defensive about missing NULs in index Jeff King
2019-04-19  5:29           ` Junio C Hamano
2019-04-18 21:17         ` [PATCH 2/3] untracked-cache: simplify parsing by dropping "next" Jeff King
2019-04-19  5:33           ` Junio C Hamano [this message]
2019-04-18 21:18         ` [PATCH 3/3] untracked-cache: simplify parsing by dropping "len" Jeff King
2019-04-18 21:24         ` [PATCH 4/3] untracked-cache: use FLEX_ALLOC to create internal structs Jeff King
2019-04-19  9:18           ` Duy Nguyen
2019-04-19 19:43             ` Jeff King

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