From: "Mattias Engdegård" <mattias.engdegard@gmail.com>
To: 58168@debbugs.gnu.org
Subject: bug#58168: string-lessp glitches and inconsistencies
Date: Thu, 29 Sep 2022 18:24:04 +0200 [thread overview]
Message-ID: <7824372D-8002-4639-8AEE-E80A6D5FEFC6@gmail.com> (raw)
We really want string< to be consistent with string= and itself since this is fundamental for string ordering in searching and sorting applications.
This means that for any pair of strings A and B, we should either have A<B, B<A or A=B.
Unfortunately:
(let* ((a "ü")
(b "\xfc"))
(list (string= a b)
(string< a b)
(string< b a)))
=> (nil nil nil)
because string< considers the unibyte raw byte 0xFC and the multibyte char U+00FC to be the same, but string= thinks they are different.
We also distinguish raw bytes by multibyte-ness:
(let* ((u "\x80")
(m (string-to-multibyte u)))
(list (string= u m)
(string< u m)
(string< m u)))
=> (nil t nil)
but this is a minor annoyance that we can live with: we strongly want string= to remain consistent with `equal` for strings.
So, what can be done? The current string< implementation uses the character order
ASCII < ub raw 80..FF = mb U+0080..U+00FF < U+0100..10FFFF < mb raw 80..FF
in conflict with string= which unifies unibyte and multibyte ASCII but not raw bytes and Latin-1.
It suggests the following alternative collation orders:
A. ASCII < ub raw 80..FF < mb U+0080..10FFFF < mb raw 80..FF
which puts all non-ASCII multibyte chars after unibyte.
B. ASCII < ub raw 80..FF < mb raw 80..FF < mb U+0080..10FFFF
which inserts multibyte raw bytes after the unibyte ones, permitting any ub-ub and mb-mb comparisons to be made using memcmp, and a slow decoding loop only required for unibyte against non-ASCII multibyte strings.
C. ASCII < mb U+0080..10FFFF < mb raw 80..FF < ub raw 80..FF
which instead moves unibyte raw bytes to after the multibyte raw range. This has the same memcmp benefit as alternative B, but may be slightly faster for ub-mb comparisons since only unibyte 80..FF need to be remapped.
Any particular preference? Otherwise, I'll go with B or C, depending on what the resulting code looks like.
next reply other threads:[~2022-09-29 16:24 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-29 16:24 Mattias Engdegård [this message]
2022-09-29 17:00 ` bug#58168: string-lessp glitches and inconsistencies Mattias Engdegård
2022-09-29 17:11 ` Eli Zaretskii
2022-09-30 20:04 ` Mattias Engdegård
2022-10-01 5:22 ` Eli Zaretskii
2022-10-01 19:57 ` Mattias Engdegård
2022-10-02 5:36 ` Eli Zaretskii
2022-10-03 19:48 ` Mattias Engdegård
2022-10-04 5:55 ` Eli Zaretskii
2022-10-04 17:40 ` Richard Stallman
2022-10-04 18:07 ` Eli Zaretskii
2022-10-06 9:05 ` Mattias Engdegård
2022-10-06 11:06 ` Eli Zaretskii
2022-10-07 14:23 ` Mattias Engdegård
2022-10-08 7:35 ` Eli Zaretskii
2022-10-14 14:39 ` Mattias Engdegård
2022-10-14 15:31 ` Eli Zaretskii
2022-10-17 12:44 ` Mattias Engdegård
2022-09-30 13:52 ` Lars Ingebrigtsen
2022-09-30 20:12 ` Mattias Engdegård
2022-10-01 5:34 ` Eli Zaretskii
2022-10-01 11:51 ` Mattias Engdegård
2022-10-01 10:02 ` Lars Ingebrigtsen
2022-10-01 10:12 ` Eli Zaretskii
2022-10-01 13:37 ` Mattias Engdegård
2022-10-01 13:43 ` Lars Ingebrigtsen
2022-10-03 19:48 ` Mattias Engdegård
2022-10-04 10:44 ` Lars Ingebrigtsen
2022-10-04 11:37 ` Eli Zaretskii
2022-10-04 14:44 ` Mattias Engdegård
2022-10-04 16:24 ` Eli Zaretskii
2022-10-06 9:05 ` Mattias Engdegård
2022-10-06 11:13 ` Eli Zaretskii
2022-10-06 12:43 ` Mattias Engdegård
2022-10-06 14:34 ` Eli Zaretskii
2022-10-07 14:45 ` Mattias Engdegård
2022-10-07 15:33 ` Eli Zaretskii
2022-10-08 17:13 ` Mattias Engdegård
2022-10-01 13:51 ` Eli Zaretskii
2022-10-01 5:30 ` Eli Zaretskii
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