Re: [PATCH 2/3] untracked-cache: simplify parsing by dropping "next"
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Apr 19, 2019, 05:33 UTC
- Message-ID
- <xmqq5zraeezm.fsf@gitster-ct.c.googlers.com>
- In-Reply-To
- <20190418211738.GB18520@sigill.intra.peff.net>
Jeff King <peff@peff.net> writes:
Show 8 quoted lines
> 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.
Show 67 quoted lines
> 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;