http://d.puremagic.com/issues/show_bug.cgi?id=4937

           Summary: std.bitmanip: Allow repeated (identical) bitfield
                    declarations
           Product: D
           Version: D2
          Platform: All
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: ah08010-d@yahoo.com


--- Comment #0 from Austin Hastings <ah08010-d@yahoo.com> 2010-09-24 18:06:53 PDT ---
I'm trying to describe an opcode layout - the arrangement of bits used by a CPU - and the resulting description is generally a union of bitfields:

opcode, displacement
opcode, register, register, register
opcode, constant
...etc

In my case, the opcode represents a common prefix, which leaves me declaring something like this in D:

opcode, displacement
    "", register, register, register
    "", constant

I would prefer, for reasons of clarity, to be able to repeat the declaration of opcode - the best comment is source code, as it were.

So I would like the bitmanip code to permit redeclaration of bitfields that are identical in all respects.

That is, obviously the names are the same, but the field width, offset, and type representation has to be the same as well.

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED
                 CC|                            |andrei@metalanguage.com
         AssignedTo|nobody@puremagic.com        |andrei@metalanguage.com


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bearophile_hugs@eml.cc changed:

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--- Comment #1 from bearophile_hugs@eml.cc 2010-09-24 18:46:51 PDT ---
See also bug 4425

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Era Scarecrow <rtcvb32@yahoo.com> changed:

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--- Comment #2 from Era Scarecrow <rtcvb32@yahoo.com> 2012-07-31 19:11:09 PDT ---
> Also, I think I'm going to request that repeated bitfield definitions be allowed if they are identical - I'd like to redeclare "opcode" rather than "".

How would you tell them apart? If i know how you may want to call them, i may be able to make something. I can understand with registers, but still need some way to work with them. Perhaps as a set then?


> So I would like the bitmanip code to permit redeclaration of bitfields that are identical in all respects.

>That is, obviously the names are the same, but the field width, offset, and type representation has to be the same as well.

Maybe....?

struct S {
    mixin(bitfields!(
        uint, "opcode", 4,
        uint, "register", 4,
        uint, "register", 4,
        uint, "register", 4
    ));
}

and using the registers would have function signature like...

struct Register {
  uint register_1;
  uint register_2;
  uint register_3;

}

//setters, likely can't be @propery
void register(uint reg1, uint reg2, uint reg3);
void register(uint[] register ...); //maybe?
void register(Register register);

//getter ??
Register register() const;

Or perhaps...

struct S {
    mixin(bitfields!(
        uint, "opcode", 4,
        uint, "reg1", 4,
        uint, "reg2", 4,
        uint, "reg3", 4
    ));
    mixin(sharedNameSet(
        "nameForGetterAndSetter",
        "struct name for returning/passing",
        "reg1", "reg2", "reg3" //named variables as a set
    ));

    //nameForGetterAndSetter's would be added here, perhaps as above.
}

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--- Comment #3 from Andrei Alexandrescu <andrei@erdani.com> 2013-02-26 08:58:34 PST ---
I think we're good as we are. OK to close?

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