[dmd-internals] Modifying the dmd compiler to add support for bitfields

[Walter Bright]

I'm glad you're aware of it.

Anyhow, the compiler (optimizer and back end) can already deal with bit fields 
as it is based on a C compiler. The bitfield ops are replaced by mask and shift 
in the cgelem.c code.

dt_t is simply a way to represent static data.

On 1/9/2012 3:35 AM, Sandeep Datta wrote:
> Hi Walter,
>
> Thanks for the reply. I am aware of the mixin based solution but the main 
> motivation for me at this point is getting to know the D compiler well. And 
> IMHO native support for bitfields will be a welcome new change. I am trying to 
> write an OS/kernel (https://github.com/SDX2000/Deimos) in D and as far as 
> machine hugging code is concerned bitfields and unions are a mainstay. The 
> mixin syntax looks jarring and alien. Please see 
> https://github.com/SDX2000/Deimos/issues/1 for what I am trying to accomplish.
>
> I am particularly curious about the dt_t data structure you seem to be using 
> how does this work?
>
> Regards,
> Sandeep Datta.
>
> On Mon, Jan 9, 2012 at 5:53 AM, Walter Bright <walter at digitalmars.com 
> <mailto:walter at digitalmars.com>> wrote:
>
>     Bit fields are already done in D using a library solution:
>
>     http://d.digitalmars.com/2.0/phobos/std_bitmanip.html
>
>
>     On 1/8/2012 7:49 AM, Sandeep Datta wrote:
>>     [Cross post from the D news group]
>>
>>     Hi All,
>>
>>     To gain a better understanding of how the D compiler works I am
>>     trying to implement support for bit fields in structures. I have
>>     modified the parser code to admit the following syntax (for now)...
>>
>>     struct A{
>>         uint:8 a;
>>         uint:5 b;
>>         uint:* unused; //Takes up the remaining space.
>>         //Raise an error when the computed size is zero.
>>     }
>>
>>     You can see my changes here...https://github.com/SDX2000/dmd
>>
>>     I have been trying to work out a strategy for modifying the compiler
>>     code generation for quite some time now but haven't been able to
>>     make much headway in this direction.
>>
>>     I would appreciate any help at this point.
>>
>>     Regards,
>>     Sandeep Datta.
>>
>>
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