Convert this C macro kroundup32 to D mixin?

[Nicholas Wilson via Digitalmars-d-learn]

On Saturday, 8 April 2017 at 11:01:34 UTC, biocyberman wrote:
> On Saturday, 8 April 2017 at 10:09:47 UTC, Mike Parker wrote:
>> T kroundup32(T)(T x) {
>>     pragma(inline, true);
>>     --(x);
>>     (x)|=(x)>>1;
>>     (x)|=(x)>>2;
>>     (x)|=(x)>>4;
>>     (x)|=(x)>>8;
>>     (x)|=(x)>>16;
>>     return ++(x);
>> }
>
>
> I also came up with this:
>
> import std.stdio;
> pragma( inline, true ):
> static int kroundup32( int x){
> --(x);
> writeln("X: ",x);
>  (x)|=(x)>>1;
> writeln("X: ",x);
>  (x)|=(x)>>2;
> writeln("X: ",x);
> (x)|=(x)>>4;
> writeln("X: ",x);
>  (x)|=(x)>>8;
> writeln("X: ",x);
>  (x)|=(x)>>16;
> writeln("X: ",x);
>  ++(x);
> writeln("X: ",x);
>
>  return x;
> }
>
> int main(){
>   int num = 31;
>   num = kroundup32(num);
>   writeln("Num:", num);
>   return 0;
> }
>
> Is this way of using pragma the same as your way? I am still 
> new to this so I want to understand more.

The ':' means that it applies to everything that follows it, so 
while it doesn't matters in this example if you had
pragma( inline, true ):
int kroundup32( int x) { ... }

auto someVeryLargeFunction( Args args)
{
     // ...
}

and then you used someVeryLargeFunction in a bunch of places then 
that would cause a lot of binary bloat.
>
> And is it a good idea to do manipulate 'num' directly so I can 
> omit 'return' and avoid re-assigning statement? That's what C 
> version does.

if you want the the function to affect the variable use a 'ref' 
as in

  void kroundup32(T)(ref T x) {
      pragma(inline, true);
      --(x);
      (x)|=(x)>>1;
      (x)|=(x)>>2;
      (x)|=(x)>>4;
      (x)|=(x)>>8;
      (x)|=(x)>>16;
      return ++(x);
  }

  int main(){
    int num = 31;
    writeln("Before: ",num); // 31
    kroundup32(num);
    writeln("After: ", num);   //32
    return 0;
  }

is it a good idea? I would not think it is necessary.

As an aside the C version has parentheses around the "x" because 
it is a macro and it is substituted as text not symbolically, 
they are not needed in D.