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From: "René Scharfe" <l.s.r@web.de>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>, git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Johannes Schindelin" <johannes.schindelin@gmx.de>,
	"Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Subject: Re: [PATCH 14/25] pickaxe -S: remove redundant "sz" check in while-loop
Date: Thu, 4 Feb 2021 17:16:29 +0100	[thread overview]
Message-ID: <4ef09db7-34f2-2fb5-b9e9-be69c7102787@web.de> (raw)
In-Reply-To: <20210203032811.14979-15-avarab@gmail.com>

Am 03.02.21 um 04:28 schrieb Ævar Arnfjörð Bjarmason:
> If we walk to the end of the string we just won't match the rest of
> the regex. This removes an optimization for simplicity's sake. In
> subsequent commits we'll alter this code more, and not having to think
> about this condition makes it easier to read.
>
> If we look at the context of what we're doing here the last thing we
> need to be worried about is one extra regex match. The real problem is
> that we keep matching after it's clear that the number of contains()
> for "A" and "B" is different. So we could be much smarter here.
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  diffcore-pickaxe.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
> index 208177bb40..8df76afb6e 100644
> --- a/diffcore-pickaxe.c
> +++ b/diffcore-pickaxe.c
> @@ -82,12 +82,11 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws)
>  		regmatch_t regmatch;
>  		int flags = 0;
>
> -		while (sz &&
> -		       !regexec_buf(regexp, data, sz, 1, &regmatch, flags)) {
> +		while (!regexec_buf(regexp, data, sz, 1, &regmatch, flags)) {

This will loop forever for regexes that match an empty string.  An
example would be /$/.  Silly, perhaps, but still I understand this check
less as an optimization and more as a correctness/robustness thing.

>  			flags |= REG_NOTBOL;
>  			data += regmatch.rm_eo;
>  			sz -= regmatch.rm_eo;
> -			if (sz && regmatch.rm_so == regmatch.rm_eo) {
> +			if (regmatch.rm_so == regmatch.rm_eo) {
>  				data++;
>  				sz--;
>  			}

Before, if the match was an empty string and there was more data after
it, then the code would consume a character anyway, in order to avoid
matching the same empty string again.  With the patch, that character
is consumed even if there is no more data.  This leaves 'data'
pointing beyond the buffer and 'sz' rolls over to ULONG_MAX.  Oops. :(

René


  reply	other threads:[~2021-02-04 16:19 UTC|newest]

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-03  3:27 [PATCH 00/25] grep: PCREv2 fixes, remove kwset.[ch] Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 01/25] grep/pcre2 tests: reword comments referring to kwset Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 02/25] grep/pcre2: drop needless assignment + assert() on opt->pcre2 Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 03/25] grep/pcre2: drop needless assignment to NULL Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 04/25] grep/pcre2: correct reference to grep_init() in comment Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 05/25] grep/pcre2: prepare to add debugging to pcre2_malloc() Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 06/25] grep/pcre2: add GREP_PCRE2_DEBUG_MALLOC debug mode Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 07/25] grep/pcre2: use compile-time PCREv2 version test Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 08/25] grep/pcre2: use pcre2_maketables_free() function Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 09/25] grep/pcre2: actually make pcre2 use custom allocator Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 10/25] grep/pcre2: move back to thread-only PCREv2 structures Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 11/25] grep/pcre2: move definitions of pcre2_{malloc,free} Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 12/25] pickaxe tests: refactor to use test_commit --append Ævar Arnfjörð Bjarmason
2021-02-03  3:27 ` [PATCH 13/25] pickaxe -S: support content with NULs under --pickaxe-regex Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 14/25] pickaxe -S: remove redundant "sz" check in while-loop Ævar Arnfjörð Bjarmason
2021-02-04 16:16   ` René Scharfe [this message]
2021-02-04 17:56     ` Junio C Hamano
2021-02-04 21:13       ` Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 15/25] pickaxe/style: consolidate declarations and assignments Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 16/25] pickaxe tests: add test for diffgrep_consume() internals Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 17/25] pickaxe tests: add test for "log -S" not being a regex Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 18/25] perf: add performance test for pickaxe Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 19/25] pickaxe -G: set -U0 for diff generation Ævar Arnfjörð Bjarmason
2021-02-03 14:26   ` Ævar Arnfjörð Bjarmason
2021-02-03 19:42     ` Junio C Hamano
2021-02-03  3:28 ` [PATCH 20/25] grep.h: make patmatch() a public function Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 21/25] pickaxe: use PCREv2 for -G and -S Ævar Arnfjörð Bjarmason
2021-02-03 20:44   ` Ævar Arnfjörð Bjarmason
2021-02-04 18:11     ` Junio C Hamano
2021-02-04 18:22   ` Junio C Hamano
2021-02-03  3:28 ` [PATCH 22/25] Remove unused kwset.[ch] Ævar Arnfjörð Bjarmason
     [not found]   ` <CAPUEspgBmuTBHVZWY9fRtjbHWBRr0zHravLL1Czepc6jmib4HA@mail.gmail.com>
2021-02-03 14:13     ` Ævar Arnfjörð Bjarmason
     [not found]       ` <CAPUEsphN7QuSVsC1Tr4xE8yQgPTtpF7wL7zbk1crQU3n-5g6JQ@mail.gmail.com>
2021-02-03 16:45         ` Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 23/25] xdiff-interface: allow early return from xdiff_emit_{line,hunk}_fn Ævar Arnfjörð Bjarmason
2021-02-03  3:28 ` [PATCH 24/25] xdiff-interface: support early exit in xdiff_outf() Ævar Arnfjörð Bjarmason
2021-02-04 18:16   ` Junio C Hamano
2021-02-03  3:28 ` [PATCH 25/25] pickaxe -G: terminate early on matching lines Ævar Arnfjörð Bjarmason
2021-02-03 12:38 ` [PATCH 00/25] grep: PCREv2 fixes, remove kwset.[ch] Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 00/22] pickaxe: test and refactoring for follow-up changes Ævar Arnfjörð Bjarmason
2021-02-16 22:23   ` Junio C Hamano
2021-02-17  1:19     ` Junio C Hamano
2021-04-12 17:15   ` [PATCH v3 00/22] pickaxe: test and refactoring for future PCRE backend Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 01/22] grep/pcre2 tests: reword comments referring to kwset Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 02/22] pickaxe tests: refactor to use test_commit --append --printf Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 03/22] pickaxe tests: add test for diffgrep_consume() internals Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 04/22] pickaxe tests: add test for "log -S" not being a regex Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 05/22] pickaxe tests: test for -G, -S and --find-object incompatibility Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 06/22] pickaxe tests: add missing test for --no-pickaxe-regex being an error Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 07/22] pickaxe: die when -G and --pickaxe-regex are combined Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 08/22] pickaxe: die when --find-object and --pickaxe-all " Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 09/22] diff.h: move pickaxe fields together again Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 10/22] pickaxe/style: consolidate declarations and assignments Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 11/22] perf: add performance test for pickaxe Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 12/22] pickaxe: refactor function selection in diffcore-pickaxe() Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 13/22] pickaxe: assert that we must have a needle under -G or -S Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 14/22] pickaxe -S: support content with NULs under --pickaxe-regex Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 15/22] pickaxe: rename variables in has_changes() for brevity Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 16/22] pickaxe -S: slightly optimize contains() Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 17/22] xdiff-interface: prepare for allowing early return Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 18/22] xdiff-interface: allow early return from xdiff_emit_line_fn Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 19/22] pickaxe -G: terminate early on matching lines Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 20/22] pickaxe -G: don't special-case create/delete Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 21/22] xdiff users: use designated initializers for out_line Ævar Arnfjörð Bjarmason
2021-04-12 17:15     ` [PATCH v3 22/22] xdiff-interface: replace discard_hunk_line() with a flag Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 01/22] grep/pcre2 tests: reword comments referring to kwset Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 02/22] test-lib-functions: document and test test_commit --no-tag Ævar Arnfjörð Bjarmason
2021-03-30 23:14   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 03/22] test-lib-functions: reword "test_commit --append" docs Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 04/22] test-lib functions: add --printf option to test_commit Ævar Arnfjörð Bjarmason
2021-03-30 23:11   ` Junio C Hamano
2021-04-12 13:19     ` Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 05/22] pickaxe tests: refactor to use test_commit --append --printf Ævar Arnfjörð Bjarmason
2021-03-30 23:26   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 06/22] pickaxe tests: add test for diffgrep_consume() internals Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 07/22] pickaxe tests: add test for "log -S" not being a regex Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 08/22] pickaxe tests: test for -G, -S and --find-object incompatibility Ævar Arnfjörð Bjarmason
2021-03-30 23:32   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 09/22] pickaxe: die when -G and --pickaxe-regex are combined Ævar Arnfjörð Bjarmason
2021-03-30 23:36   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 10/22] pickaxe: die when --find-object and --pickaxe-all " Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 11/22] diff.h: move pickaxe fields together again Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 12/22] pickaxe/style: consolidate declarations and assignments Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 13/22] perf: add performance test for pickaxe Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 14/22] pickaxe: refactor function selection in diffcore-pickaxe() Ævar Arnfjörð Bjarmason
2021-03-30 23:45   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 15/22] pickaxe: assert that we must have a needle under -G or -S Ævar Arnfjörð Bjarmason
2021-03-30 23:50   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 16/22] pickaxe -S: support content with NULs under --pickaxe-regex Ævar Arnfjörð Bjarmason
2021-03-30 23:54   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 17/22] pickaxe: rename variables in has_changes() for brevity Ævar Arnfjörð Bjarmason
2021-02-16 11:57 ` [PATCH v2 18/22] pickaxe -S: slightly optimize contains() Ævar Arnfjörð Bjarmason
2021-03-30 23:58   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 19/22] xdiff-interface: allow early return from xdiff_emit_{line,hunk}_fn Ævar Arnfjörð Bjarmason
2021-03-31  0:04   ` Junio C Hamano
2021-02-16 11:57 ` [PATCH v2 20/22] xdiff-interface: support early exit in xdiff_outf() Ævar Arnfjörð Bjarmason
2021-02-16 11:58 ` [PATCH v2 21/22] pickaxe -G: terminate early on matching lines Ævar Arnfjörð Bjarmason
2021-03-31  0:11   ` Junio C Hamano
2021-02-16 11:58 ` [PATCH v2 22/22] pickaxe -G: don't special-case create/delete Ævar Arnfjörð Bjarmason
2021-03-31  0:14   ` Junio C Hamano

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