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From: Vir Campestris <vir.campestris@invalid.invalid>
Newsgroups: comp.lang.c
Subject: Re: What is your opinion about unsigned int u = -2 ?
Date: Mon, 12 Aug 2024 11:47:11 +0100
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On 11/08/2024 21:53, James Kuyper wrote:
> On 8/11/24 16:08, Vir Campestris wrote:
> ...
>> "Converting -1 to an unsigned type always sets all the bits"
>>
>> In any normal twos complement architecture that's the case. But there
>> are a few oddballs out there where -1 is +1, except that the dedicated
>> sign bit is set.
> 
> There may be hardware where that is true, but a conforming
> implementation of C targeting that hardware cannot use the hardware's
> result. It must fix up the result produced by the hardware to match the
> result required by the C standard.
> 

On 11/08/2024 21:45, Richard Damon wrote:
 >
 > But, when that -1 value is converted to an unsigned type, that VALUE
 > will be adjusted modulo the appropriate power of two.
 >
 > signed to unsigned conversion works on VALUE, not bit pattern, so is
 > invariant with the representation of the negative values.
 >
 > Yes, in a union with a signed and unsigned, the type punning will let
 > you see the representation of the types, but assignment works on values.

Ah, thank you both. It's academic interest only of course!

Andy