Re: hmm..

Valdis.Kletnieks_at_vt.edu
Date: 12/25/03

  • Next message: Srivatsa Vaddagiri: "Re: [PATCH 1/2] kthread_create" 
    To: Linus Torvalds <torvalds@osdl.org>
Date:	Thu, 25 Dec 2003 02:56:37 -0500

    On Mon, 22 Dec 2003 13:31:51 PST, Linus Torvalds said:

    > - algorithmically, there aren't that many ways to test whether a
    > character is a number or not. That's _especially_ true in
    > C, where a macro must not use it's argument more than once. So for
    > example, the "obvious" implementation of "isdigit()" (which tests for
    > whether a character is a digit or not) would be
    >
    > #define isdigit(x) ((x) >= '0' && (x) <= '9')
    >
    > but this is not actually allowed by the C standard (because 'x' is used
    > twice).

    Somebody tell IBM that. From the AIX 4.3.3 and 5.1 /usr/include/ctype.h:

    #define _VALC(__c) ((__c)>=0&&(__c)<=256)
    #define _IS(__c,__m) (__OBJ_DATA(__lc_ctype)->mask[__c] & __m)
    #define isalpha(__a) (_VALC(__a)?_IS(__a,_ISALPHA):0)
    #define isalnum(__a) (_VALC(__a)?_IS(__a,_ISALNUM):0)
    #define iscntrl(__a) (_VALC(__a)?_IS(__a,_ISCNTRL):0)
    #define isdigit(__a) (_VALC(__a)?_IS(__a,_ISDIGIT):0)
    #define isgraph(__a) (_VALC(__a)?_IS(__a,_ISGRAPH):0)
    #define islower(__a) (_VALC(__a)?_IS(__a,_ISLOWER):0)
    #define isprint(__a) (_VALC(__a)?_IS(__a,_ISPRINT):0)
    #define ispunct(__a) (_VALC(__a)?_IS(__a,_ISPUNCT):0)
    #define isspace(__a) (_VALC(__a)?_IS(__a,_ISSPACE):0)
    #define isupper(__a) (_VALC(__a)?_IS(__a,_ISUPPER):0)
    #define isxdigit(__a) (_VALC(__a)?_IS(__a,_ISXDIGIT):0)
    #define isascii(c) (!((c) & ~0177))

    You'd be *amazed* how far through memory a 'while (isalpha(*s++)) {..};' can go
    (which in fact is how I discovered this blecherousness).

    The AIX 4.3 support I contributed to Sendmail 8.9.0 back in Feb 98 included a
    work-around because IBM refused to fix it on the grounds that the VALC macro
    was to protect against a SEGV if the macro was fed an 'int' rather than a
    'char' (why they didn't just use 'mask[__c & 255]' is beyond me), and that you
    only got hit if you compiled(*) with -D_ILS_MACROS. At least IBM eventually fixed
    isascii(), which was originally broken the same way....

    Feel free to file this under "Code we can prove that IBM never contributed" :)

    (*) The default is to use actual function calls due to locale considerations - building
    with _ILS_MACROS provides a measured 30%+ CPU savings for Sendmail, which
    doesn't care if it's nailed into a 'LANG=C' environ anyhow...

    -
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  • Next message: Srivatsa Vaddagiri: "Re: [PATCH 1/2] kthread_create"

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