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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: Fri, 21 Jan 2022 17:12:14 -0800
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Bonita Montero <Bonita.Montero@gmail.com> writes:

> Am 21.01.2022 um 15:01 schrieb Tim Rentsch:
>
>> Bonita Montero <Bonita.Montero@gmail.com> writes:
>>
>>> Am 21.01.2022 um 04:24 schrieb Tim Rentsch:
>>>
>>>> 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.
>>>
>>> Doesn't help because c isn't a constant.
>>
>> It's hard to know what to say to such an obviously
>> inapplicable comment.
>
> If your exchanges would result in a constant instead of a
> calucaltion they would be favourable.  But the overhead for
> your swapped calculation is exactly the same and the code isn't
> more readable than before.

Apparently you don't understand that your comment has no bearing
on what I was talking about.