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Groups > comp.lang.c > #164499
| From | Tim Rentsch <tr.17687@z991.linuxsc.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: on an analogy for verifying whether another digit fits (into an unsigned type) |
| Date | 2022-01-20 19:24 -0800 |
| Organization | A noiseless patient Spider |
| Message-ID | <86fsphrcsu.fsf@linuxsc.com> (permalink) |
| References | <86mtjws9cg.fsf@levado.to> |
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.
> (*) 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;
> }
It's better to write the code so the funny division test
isn't needed:
uint64_t
array_to_uint64( char *s0, uint64_t *u ){
char *s = s0;
uint64_t r, d, nr;
for( r = 0; d = *s-'0', nr = r*10+d, d < 10; r = nr, s++ ){
if( r > nr ) return -1;
}
return *u = r, s-s0;
}
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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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