Re: Can we lie to memchr?

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From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Can we lie to memchr?
Date	Sun, 03 Sep 2023 11:22:10 -0700
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Kaz Kylheku <864-117-4973@kylheku.com> writes:

> You would think that memchr can be used to test whether a string is
> longer than N without traversing it.  For instance we can take a
> gigabyte-long character string and efficiently test wheether it is
> shorter than 10 characters:
>
>   memchr(gigastr, 0, 10) == 0
>
> if a null is found within the first 10 bytes, then its length
> is 10 or more.
>
> But suppose a 7 byte string is passed (length 6).
>
> That *object* is smaller than n;  it does not have an "initial sequence
> of n characters" for memchr to search.
>
> ISO C doesn't say that bytes of the initial sequence which are
> beyond are sought-after value shall not be accessed by memchr.  [...]

It does, and has for more than 10 years.

Thread

Can we lie to memchr? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-03 17:59 +0000
  Re: Can we lie to memchr? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-03 11:22 -0700
    Re: Can we lie to memchr? Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-03 18:58 +0000
  Re: Can we lie to memchr? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 19:30 +0100

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