[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Questionable code in handling of wordend in the regexp engine in reg
From: |
Stefan Monnier |
Subject: |
Re: Questionable code in handling of wordend in the regexp engine in regex-emacs.c |
Date: |
Sat, 23 Feb 2019 18:15:55 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
> Primarily, there is an
>
> UPDATE_SYNTAX_TABLE (charpos);
>
> before determining the syntax of the previous character, which seems OK.
> Later on, before determining the syntax of the next character, we have:
>
> UPDATE_SYNTAX_TABLE_FORWARD (charpos);
>
> . Between these two calls, charpos hasn't been changed.
Good spotting.
> Surely the argument to the second occurrence should be (charpos + 1)?
I believe it's instead the other one that needs to use "charpos - 1"
because the UPDATE_SYNTAX_TABLE is called just before reading the char
*before* charpos (see patch below).
> Also, probably less importantly, there is
>
> GET_CHAR_AFTER (c2, d, dummy);
>
> , whereas at the same place in the handler for case symend: we have
> instead
>
> c2 = RE_STRING_CHAR (d, target_multibyte);
>
> . Is the effect of these macros identical, or is one of them up to
> date, and the other one really needs updating as well, for correct
> functionality?
According to my reading of the code, they're identical in multibyte
buffers not in unibyte buffers where RE_STRING_CHAR just returns a value
between 0 and 255 (i.e. ASCII or Latin-1 more or less), whereas
GET_CHAR_AFTER will return either an ASCII char (0..127) or a raw-byte
char (4194176..4194303).
I think it's more correct to return a raw-byte char (4194176..4194303),
so I'd tend to think that GET_CHAR_AFTER is the better choice, but
please don't quote me on this.
> I came across these whilst investigating bug #34525. Making the
> indicated changes to regex-emacs.c sadly doesn't help solve the symptoms
> of that bug. :-(
Does the patch below help?
Stefan
diff --git a/src/regex-emacs.c b/src/regex-emacs.c
index b667a43a37..72fb5ec561 100644
--- a/src/regex-emacs.c
+++ b/src/regex-emacs.c
@@ -4813,7 +4813,7 @@ re_match_2_internal (struct re_pattern_buffer *bufp,
re_char *string1,
int dummy;
ptrdiff_t offset = PTR_TO_OFFSET (d) - 1;
ptrdiff_t charpos = SYNTAX_TABLE_BYTE_TO_CHAR (offset);
- UPDATE_SYNTAX_TABLE (charpos);
+ UPDATE_SYNTAX_TABLE (charpos - 1);
GET_CHAR_BEFORE_2 (c1, d, string1, end1, string2, end2);
s1 = SYNTAX (c1);