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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: how cast works?
Date: Fri, 9 Aug 2024 16:22:30 -0300
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Em 8/9/2024 4:03 PM, Keith Thompson escreveu:
> Thiago Adams <thiago.adams@gmail.com> writes:
> [...]
>> This part was always clear to me:
>>
>> "They  are not performed 'in-place', any more than writing `a + 1`
>> changes the value of `a`."
>>
>> Lets take double to int.
>>
>> In this case the bits of double needs to be reinterpreted (copied to) int.
> 
> The word "reinterpreted" usually refers to taking a given representation
> (sequence of bits) and treating it as a value of a specified type
> *without changing the bits*.  (<OT>C++ even has "reintrepret_cast" as a
> keyword.</OT>)
> 
> Converting from int to double does not reinterpret the bits.  It creates
> a new value that is mathematically equal (or nearly so) to the operand
> value.
> 
>> So the answer "how it works" can be
>>
>> always/generally machine has a instruction to do this
>>
>> or.. this is defined by the IIE ... standard as ...
> 
> Do you mean the IEEE standard?  As always, the C standard defines the
> semantics of conversions.  For an implementation that claims to conform
> to IEEE floating-point standard (ISO/IEC 60559), the semantics are
> specified more precisely.
> 

Yes. maybe the conversion double to int for instance, is related with 
truncation, and this is specified on IEEE.
The inverse int to double is similar. For instance ULLONGMAX to double.

I guess all computers languages works in the same way today because also 
hardware works following the floating point standards.


--

We already have many topics in one...but I am adding one more. :D 
_Decimal32 , _Decimal64 etc..

C23 have these new types. I think it has to me emulated because it is 
not something implemented on hardware.

C started as being something more hardware related, but now we have 
complex types, bool, _Decimal.. I think all these types are "emulated".