Re: how cast works?

On 08/08/2024 12:14, Thiago Adams wrote:

On 07/08/2024 17:00, Dan Purgert wrote:

On 2024-08-07, Thiago Adams wrote:

How cast works?
Does it changes the memory?
For instance, from "unsigned int" to "signed char".
Is it just like discarding bytes or something else?
[...]

>
I don't know what happens when you're changing datatype lengths, but if
they're the same length, it's just telling the compiler what the
variable should be treated as (e.g. [8-bit] int to char)
>

>
I also would like to understand better signed and unsigned.
There is no such think as "signed" or "unsigned" register, right?

>
"Signed" just means the first bit indicates negative.
>
So an "unsigned" 8 bit integer will have the 256 values ranging from
>
  0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 = 0
       (0b00000000)
>
               TO
>
  128 + 64 + 32 + 16 + 8 +4 + 2 + 1 = 255
       (0b11111111)
>
>
Whereas a "signed" 8 bit integer will have the 256 values ranging from
>
   (-128) + 0 + 0 + 0 + 0 + 0 + 0 + 0 = -128
       (0b10000000)
>
               TO
>
   0 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 127
       (0b01111111)
>
At least in two's compliment (but that's the way it's done in C)
>
>

How about floating point?

>
Floating point is a huge mess, and has a few variations for encoding;
though I think most C implementations use the one from the IEEE on 1985
(uh, IEEE754, I think?)
>

   I didn't specify properly , but my question was more about floating point registers. I think in this case they have specialized registers.

Try godbolt.org. Type in a fragment of code that does different kinds of casts (it needs to be well-formed, so inside a function), and see what code is produced with different C compilers.
Use -O0 so that the code isn't optimised out of existence, and so that you can more easily match it to the C source.