[Issue 6829] Unsigned rotate standard function in Phobos

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http://d.puremagic.com/issues/show_bug.cgi?id=6829



--- Comment #9 from Iain Buclaw <ibuclaw at ubuntu.com> 2013-07-10 03:49:49 PDT ---
(In reply to comment #8)
> (In reply to comment #6)
> > (In reply to comment #5)
> > > I think this should be a recognizable rotate left function:
> > > 
> > >     private static uint rol(in uint x, in uint y) pure nothrow {
> > >         return (x << y) | (x >> (32 - y));
> > >     }
> > 
> > It is (in gdc with -O :)
> > 
> > _D3rol3rolFNaNbxkxkZk:
> >         mov x, %eax
> >         mov y, %ecx
> >         rol %cl, %eax
> >         ret
> 
> 
> Both dmd and ldc2 recognize the patterns:
> 

Excellent, so could put these as templates then. :)

T rol (T)(in T x, in uint y) pure nothrow
{
  return cast(T)((x << y) | (x >> ((T.sizeof * 8) - y)));
}

T ror (T)(in T x, in uint y) pure nothrow
{
  return cast(T)((x >> y) | (x << ((T.sizeof * 8) - y)));
}


// Tests to check for assembly output.
extern ubyte xb;
extern ushort xs;
extern uint xi;
extern ulong xl;

extern uint yi;

{
  rol (xb, yi);   // rolb
  ror (xb, yi);   // rorb

  rol (xs, yi);   // rolw
  ror (xs, yi);   // rorw

  rol (xi, yi);   // roll
  ror (xi, yi);   // rorl

  rol (xl, yi);   // version(X86_64) rolq
  ror (xl, yi);   // version(X86_64) rorq
}

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