[M3commit] CVS Update: cm3

[Jay]

 Is CASP trivially constructed from CAS? 

 CASP(value, old, new) == (CAS(value, old, new) == old) ? 

 P for predicate? ie: returns boolean? 


 Or a) am I just wrong? 
    b) sometimes it is more efficient implemented more directly? 
 
 
For example, I know "InterlockedIncrement" can be implemented as an infinite retry loop around compare_and_swap, but that doesn't seem most efficient, e.g:
 
 
long InterlockedIncrement(volatile long* p):
  while (1)
    long old = *p;
    if (InterlockedCompareExchange(p, old, old + 1) == old)
      return (old + 1);
 
 
 
I assume we don't care about 386 support, nor maybe even 486.
Somewhere along the line way back "lock cmpxchg8b" is not supported.
 
 
 - Jay


----------------------------------------
> Date: Tue, 17 Feb 2009 05:45:48 +0000
> To: m3commit at elegosoft.com
> From: hosking at elego.de
> Subject: [M3commit] CVS Update: cm3
>
> CVSROOT: /usr/cvs
> Changes by: hosking at birch. 09/02/17 05:45:48
>
> Modified files:
> cm3/m3-sys/m3front/src/builtinOps/: BuiltinOps.m3 m3makefile
> cm3/m3-sys/m3front/src/misc/: CG.i3 CG.m3 Token.m3
> cm3/m3-sys/m3front/src/values/: Formal.i3 Formal.m3
> Added files:
> cm3/m3-sys/m3front/src/builtinOps/: Cas.i3 Cas.m3 CasP.i3
> CasP.m3
>
> Log message:
> Experimental support for compare_and_swap (CAS) and compare_and_set (CASP) builtin operations.
> CAS is defined as follows:
>
> CAS(v, o, n): BaseType(v)
>
> where v is an integer variable (INTEGER/LONGINT), and o and n are assignable to v,
> atomically sets v to value n, so long as the previous value of v is o, returning the previous
> value of v in either case.
>
> Similarly, CASP is defined as:
>
> CASP(v, o, n): BOOLEAN
>
> atomically sets v to n, so long as the previous value of v is o, returning TRUE if the
> comparison is successful and n was assigned to v.
>
> I may yet generalize these to permit v to have any ordinal type.
> In unsafe modules I may also permit v to be a subtype of ADDRESS.
>