string-downcase does not downcase character 224

[Matt Kaufmann]

The CL HyperSpec says (https://www.lispworks.com/documentation/HyperSpec/Body/f_stg_up.htm#string-downcase): "string-downcase is like string-upcase except that all uppercase characters are replaced by the corresponding lowercase characters (using char-downcase)." But that fails in the following example: the two results should be the same (note that they are both 224 in CCL, LispWorks, CMUCL, and Allegro CL, and they are both 192 in GCL).

    * (char-code (char-downcase (code-char 192)))
    224
    * (let ((s (string-downcase (coerce (list (code-char 192)) 'string))))
        (char-code (char s 0)))
    192
    *

Interestingly, going in the other direction (using string-upcase) works as expected.

    * (let ((s (string-upcase (coerce (list (code-char 224)) 'string))))
        (char-code (char s 0)))
    192
    *

Apparently (code-char 224) is the only standard character with this problem.

    * (loop for i from 0 to 255
            as c = (code-char i)
            when (and (lower-case-p c)
                      (let ((s (coerce (list c) 'string)))
                        (not (equal (string-downcase (string-upcase s)) s))))
            collect i)
    (224)
    *

I got the results above on MacOS using the latest SBCL:

    ~$ uname -a
    Darwin Matts-MacBook-Pro.local 19.6.0 Darwin Kernel Version 19.6.0: Tue Jun 21 21:18:39 PDT 2022; root:xnu-6153.141.66~1/RELEASE_X86_64 x86_64
    ~$ sbcl --version
    SBCL 2.4.5
    ~$

    * *features*
    (:ARENA-ALLOCATOR :X86-64 :GENCGC :64-BIT :ANSI-CL :BSD :COMMON-LISP :DARWIN
     :IEEE-FLOATING-POINT :LITTLE-ENDIAN :MACH-O :PACKAGE-LOCAL-NICKNAMES :SB-LDB
     :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL :UNIX)
    *

On Linux I used the preceding SBCL version:

    cyan:~% uname -a
    Linux cyan 5.4.0-182-generic #202-Ubuntu SMP Fri Apr 26 12:29:36 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
    cyan:~% sbcl --version
    SBCL 2.4.4
    cyan:~%

    * *features*
    (:ARENA-ALLOCATOR :X86-64 :GENCGC :64-BIT :ANSI-CL :COMMON-LISP :ELF
     :IEEE-FLOATING-POINT :LINUX :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES :SB-LDB
     :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL :UNIX)
    *