[QUESTION] Usage of negative number notations on unsigned numbers.

[Karthik B K]

On 27/11/23 19:16, Andreas Schwab wrote:
> On Nov 27 2023, Karthik B K wrote:
>
>> What's the encoding of (2^32-1)UL and (2^64-1)UL ?
> A value does not have an encoding.  Only a memory location does.
>
So does a register (container of bits), and a type (signed, unsigned, 
float).

The "encoding" is dependent on the "container" (reg or mem) and "type" 
(signed, unsigned, float).

The same bits (11...11) would reflect very different values (-1, 2^32-1, 
quiteNaN).

The container of (2^32-1) is UInt. 32b unsigned integer. -1 cannot be 
represented in a 32b unsigned int.


I'm trying to say, that the unary operator (-) in the expression (-1UL) 
is an integer arithmetic operator.

The unary operator (-) when applied to an unsigned type, results in the 
_negative_ of it's (promoted as per _usual arithmetic conversions_) 
operand, which in this case, is a signed integer.

The result will retain this type. Are we assuming an implicit cast ?

This looks like an illegal set of operations to create the bit pattern 
we desire (11...11) for an unsigned int.


Simply put, a -1 in a UL is an oxymoron. Don't you think ?

Please correct me if I'm wrong.


karthik.

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