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From: Lars Ingebrigtsen <larsi@gnus.org>
To: "Mattias Engdegård" <mattias.engdegard@gmail.com>
Cc: 58168@debbugs.gnu.org
Subject: bug#58168: string-lessp glitches and inconsistencies
Date: Fri, 30 Sep 2022 15:52:12 +0200	[thread overview]
Message-ID: <877d1l55rn.fsf@gnus.org> (raw)
In-Reply-To: <7824372D-8002-4639-8AEE-E80A6D5FEFC6@gmail.com> ("Mattias Engdegård"'s message of "Thu, 29 Sep 2022 18:24:04 +0200")

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

> 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.

You also have

(string 4194176)
=> "\200"
"\x80"
=> "\200"

which are kinda equal in some ways, and not in other ways.

> 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.

I think A makes the most intuitive sense, somehow.  But perhaps my
intuition is off.





  parent reply	other threads:[~2022-09-30 13:52 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-29 16:24 bug#58168: string-lessp glitches and inconsistencies Mattias Engdegård
2022-09-29 17:00 ` 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 [this message]
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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