Re: on an analogy for verifying whether another digit fits (into an unsigned type)

From	Meredith Montgomery <mmontgomery@levado.to>
Newsgroups	comp.lang.c
Subject	Re: on an analogy for verifying whether another digit fits (into an unsigned type)
Date	2022-01-28 22:25 -0300
Organization	Aioe.org NNTP Server
Message-ID	<86k0ej8hai.fsf@levado.to> (permalink)
References	<86mtjws9cg.fsf@levado.to> <86fsphrcsu.fsf@linuxsc.com>

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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

> Meredith Montgomery <mmontgomery@levado.to> writes:
>
>> I've been trying to think of an analogy for the verification
>>
>>       if( ((UINT64_MAX - c) / 10) >= r)
>>         r = r * 10 + c;
>>       else return -1; /* doesn't fit */
>>
>> in the procedure below.  [...]
>
> No analogy needed.  The condition that needs to be
> satisfied is
>
>     r * 10 + c <= UINT64_MAX
>
> which is the same as
>
>     r * 10 <= UINT64_MAX - c
>
> which is the same as
>
>     r <= (UINT64_MAX - c) / 10
>
> which is the same as
>
>     (UINT64_MAX - c) / 10 >= r
>
> giving the expression in the if() test.  Done.

That's a brilliant explanation!

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on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-15 23:27 -0300
  Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-16 18:44 +0000
    Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:48 -0300
      Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-17 17:27 +0000
        Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-17 18:06 +0000
          Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-17 20:59 +0000
            Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-18 01:01 +0000
        Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 22:15 -0300
          Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-29 02:36 +0000
            Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-30 09:12 -0300
              Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-30 15:13 +0000
  Re: on an analogy for verifying whether another digit fits (into an unsigned type) Öö Tiib <ootiib@hot.ee> - 2022-01-16 12:15 -0800
    Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 09:53 -0300
      Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-17 10:12 -0300
  Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-19 08:52 +0100
    Re: on an analogy for verifying whether another digit fits (into an unsigned type) Öö Tiib <ootiib@hot.ee> - 2022-01-19 06:08 -0800
      Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-19 16:31 +0100
        Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-19 18:02 +0100
          Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-19 18:27 +0000
            Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-19 19:44 +0100
              Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-20 08:08 +0100
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Öö Tiib <ootiib@hot.ee> - 2022-01-20 09:47 -0800
            Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-19 18:46 +0000
              Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-19 20:59 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-19 21:12 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-19 22:25 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-20 03:49 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-20 10:05 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-20 17:02 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-20 19:20 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-20 19:31 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-23 14:26 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 00:13 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2022-01-24 00:38 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 01:09 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-24 01:15 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 11:21 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-24 15:54 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-24 13:08 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-24 22:51 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-24 15:57 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 16:52 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Öö Tiib <ootiib@hot.ee> - 2022-01-24 10:17 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-24 18:23 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-24 13:15 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 11:51 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-23 17:38 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 11:22 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-24 15:51 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-24 22:03 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-24 15:33 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-25 00:09 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-24 21:14 -0800
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Manfred <invalid@invalid.add> - 2022-01-26 21:01 +0100
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bart <bc@freeuk.com> - 2022-01-26 20:53 +0000
                Re: on an analogy for verifying whether another digit fits (into an unsigned type) Manfred <noname@add.invalid> - 2022-01-27 03:42 +0100
  Re: on an analogy for verifying whether another digit fits (into an unsigned type) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-20 19:24 -0800
    Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-21 08:07 +0100
      Re: on an analogy for verifying whether another digit fits (into an unsigned type) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-21 06:01 -0800
        Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-21 17:59 +0100
          Re: on an analogy for verifying whether another digit fits (into an unsigned type) scott@slp53.sl.home (Scott Lurndal) - 2022-01-21 17:41 +0000
            Re: on an analogy for verifying whether another digit fits (into an unsigned type) Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-21 19:26 +0100
          Re: on an analogy for verifying whether another digit fits (into an unsigned type) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-21 17:12 -0800
    Re: on an analogy for verifying whether another digit fits (into an unsigned type) Meredith Montgomery <mmontgomery@levado.to> - 2022-01-28 22:25 -0300

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