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

From	Meredith Montgomery <mmontgomery@levado.to>
Newsgroups	comp.lang.c
Subject	on an analogy for verifying whether another digit fits (into an unsigned type)
Date	2022-01-15 23:27 -0300
Organization	Aioe.org NNTP Server
Message-ID	<86mtjws9cg.fsf@levado.to> (permalink)

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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.  

I thought of the following, which doesn't quite work.  Consider fill up
a bucker of water where we must make sure not to overflow.  We're given
one last glass of water to throw in the bucket and we need a strategy to
know whether that last glass would or would not overflow the bucket.  We
have all the quantities involved --- the maximum volume in the bucket,
the volume of the glass of water and the volume currently in the bucket.
Say the maximum is M, r is the current volume and c is the volume of
water in the glass.  The subtraction M - c represents the amount of
water that would be the exact amount to fill up the bucket completely
without a drop overflowing if we add c to the bucket.  So, if the
current volume is greater than M - c, then we can't put c in the bucket.

That gives the general strategy, but it's not too good because there's
nothing in this analogy that matches the division by 10.  I could of
course make a up world in which every glass of water you throw in a
bucket makes the volume in the bucket to be multiplied by a factor of 10
before the glass of water goes in.  The purpose of an analogy is to make
something odd look natural, so this is a poor analogy.

Any cool ideas?  Thank you.

(*) The procedure

uint64_t array_to_uint64(char *s, uint64_t *u) 
{
  uint64_t pos;
  uint64_t r;
  uint64_t c;

  pos = 0; r = 0;

  for ( ;; ) {
    c = (uint64_t) (unsigned char) (s[pos] - '0');
    if (c < 10) {
      if( ((UINT64_MAX - c) / 10) >= r) 
        r = r * 10 + c;
      else return -1; /* doesn't fit */
      ++pos; continue;
    }
    break;
  }

  *u = r;
  return pos;
}

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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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