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Groups > comp.lang.c > #152263

Re: How many wide characters may mbstowcs store?

From Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups comp.lang.c
Subject Re: How many wide characters may mbstowcs store?
Date 2020-05-12 20:02 +0100
Organization A noiseless patient Spider
Message-ID <87ftc5dlif.fsf@bsb.me.uk> (permalink)
References (3 earlier) <86mu6exxpw.fsf@linuxsc.com> <n5guG.283633$Xk.216585@fx46.iad> <r9c5ha$db2$1@solani.org> <7YguG.179866$2U3.164806@fx04.iad> <0464d036-5ce1-4a13-b92b-a4ff66aa1af4@googlegroups.com>

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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:

> On Monday, 11 May 2020 19:38:04 UTC+1, Scott Lurndal  wrote:
<cut>
>> The purpose of the standard is to provide a contract between the
>> application and the implementation.
>> 
>> The requirements in the standard describe what the implementation is allowed
>> to do.  Explicitly.  It cannot write beyond the 'n-1'th element of the
>> destination, and cannot read beyond the nul-byte in the source.

If the implementation writes beyond any converted wide null it must
pretend that it didn't because the return result counts the number of
modified locations.  As a result, it can only write the value that was
there before (that's technically a modification in C terms, but it's one
the implementation can lie about).

<cut>
> Note that if we know that the buffers are correctly aligned and the size
> is a multiple of the natural word size, probably 8 bytes, we can implement
> the function in such as way as to always read and write multiples of 8 bytes,
> and construct the write in registers. As memory access is usually the
> rate limiting operation, tis might well be faster than trying to
> detect the exact output buffer end.

Is there a way that can be useful when the "extra" entries -- those
after any convert wide null -- must remain unchanged?  Seems unlikely,
but it's not my area of expertise.

-- 
Ben.

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How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 13:30 +0200
  Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 13:55 +0200
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 14:01 +0200
      Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 09:08 -0400
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:19 +0200
        Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 18:32 +0200
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 18:59 +0200
          Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:42 +0000
            Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:30 +0200
            Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-12 00:29 -0400
              Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-12 14:41 +0200
              Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-12 16:19 +0200
  Re: How many wide characters may mbstowcs store? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-05-11 13:03 +0100
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 14:07 +0200
  Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:20 +0200
    Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:31 +0200
    Re: How many wide characters may mbstowcs store? Barry Schwarz <schwarzb@delq.com> - 2020-05-11 10:06 -0700
  Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 15:58 +0200
    Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 10:24 -0400
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 16:52 +0200
      Re: How many wide characters may mbstowcs store? Manfred <noname@add.invalid> - 2020-05-11 18:55 +0200
    Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 15:51 +0000
      Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:01 +0200
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:33 +0000
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:57 +0200
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:17 +0000
              Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 19:41 +0000
                Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 20:01 +0000
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:19 +0000
    Re: How many wide characters may mbstowcs store? Florian Weimer <fw@deneb.enyo.de> - 2020-05-11 20:24 +0200
      Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:59 +0200
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 19:17 +0000
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 21:24 +0200
        Re: How many wide characters may mbstowcs store? Florian Weimer <fw@deneb.enyo.de> - 2020-05-11 22:30 +0200
  Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:44 +0200
    Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 16:54 +0200
      Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 16:57 +0200
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 17:07 +0200
          Re: How many wide characters may mbstowcs store? Bonita Montero <Bonita.Montero@gmail.com> - 2020-05-11 17:08 +0200
          Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-11 11:25 -0400
      Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-11 09:06 -0700
        Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:05 +0200
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 19:19 +0200
            Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-23 07:51 -0700
              Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-23 20:27 +0200
                Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-23 14:25 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-26 07:09 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-26 07:14 -0700
                Re: How many wide characters may mbstowcs store? Spiros Bousbouras <spibou@gmail.com> - 2020-05-26 16:00 +0000
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-29 21:23 -0700
                Re: How many wide characters may mbstowcs store? Spiros Bousbouras <spibou@gmail.com> - 2020-05-30 20:08 +0000
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-03 08:46 -0700
                Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-03 10:18 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-23 05:35 -0700
                Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-06-26 06:32 -0700
                Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-09-02 09:19 -0700
                Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-09-02 19:50 -0700
                Re: How many wide characters may mbstowcs store? raltbos@xs4all.nl (Richard Bos) - 2020-06-04 20:34 +0000
        Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 17:39 +0000
          Re: How many wide characters may mbstowcs store? Autist <autist69@gmail.com> - 2020-05-11 19:42 +0200
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-11 20:28 +0200
            Re: How many wide characters may mbstowcs store? scott@slp53.sl.home (Scott Lurndal) - 2020-05-11 18:37 +0000
              Re: How many wide characters may mbstowcs store? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-05-11 11:50 -0700
                Re: How many wide characters may mbstowcs store? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-05-12 20:02 +0100
                Re: How many wide characters may mbstowcs store? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-05-12 13:12 -0700
          Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 19:56 +0000
          Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-05-24 16:49 -0700
      Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-11 14:19 -0700
        Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-11 14:22 -0700
          Re: How many wide characters may mbstowcs store? Philipp Klaus Krause <pkk@spth.de> - 2020-05-12 09:17 +0200
        Re: How many wide characters may mbstowcs store? raltbos@xs4all.nl (Richard Bos) - 2020-05-24 16:12 +0000
          Re: How many wide characters may mbstowcs store? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-05-24 15:10 -0700
          Re: How many wide characters may mbstowcs store? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-05-24 22:58 -0400
  Re: How many wide characters may mbstowcs store? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-05-11 20:07 +0000
  Re: How many wide characters may mbstowcs store? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2020-06-25 21:42 -0700
    Re: How many wide characters may mbstowcs store? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-06-28 06:32 -0700

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