[M3devel] constants/offsetof?

[Tony Hosking]

I really don't understand yet what you are trying to achieve.
Do you have a distilled example?


Antony Hosking | Associate Professor | Computer Science | Purdue University
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On Dec 27, 2010, at 2:15 AM, Jay K wrote:

> Is it unreasonble to expect more/all of these to be constant?
> 
> 
> UNSAFE MODULE bug1;
> 
> 
> TYPE T1 = RECORD i,j:INTEGER END;
> 
> 
> <*NOWARN*>VAR a:T1;
> <*NOWARN*>CONST b: UNTRACED REF T1 = NIL;
> <*NOWARN*>CONST c: ADDRESS = ADR(a); (* line 7 *)
> <*NOWARN*>CONST d: ADDRESS = ADR(a.i);
> <*NOWARN*>CONST e: ADDRESS = ADR(a.j);
> <*NOWARN*>CONST f: INTEGER = ADR(a.j) - NIL;
> <*NOWARN*>CONST g: ADDRESS = ADR(b.i);
> <*NOWARN*>CONST h: ADDRESS = ADR(b.j);
> <*NOWARN*>CONST i: INTEGER = ADR(b.j) - NIL;
> 
> <*NOWARN*>VAR vc: ADDRESS := ADR(a);
> <*NOWARN*>VAR vd: ADDRESS := ADR(a.i);
> <*NOWARN*>VAR ve: ADDRESS := ADR(a.j);
> <*NOWARN*>VAR vf: INTEGER := ADR(a.j) - NIL; (* oops, didn't mean this one *)
> <*NOWARN*>VAR vg: ADDRESS := ADR(b.i);
> <*NOWARN*>VAR vh: ADDRESS := ADR(b.j);
> <*NOWARN*>VAR vi: INTEGER := ADR(b.j) - NIL;
> 
> BEGIN
> END bug1.
> 
> 
> "../src/bug1.m3", line 7: value is not constant
> "../src/bug1.m3", line 8: value is not constant
> "../src/bug1.m3", line 9: value is not constant
> "../src/bug1.m3", line 10: value is not constant
> "../src/bug1.m3", line 11: value is not constant
> "../src/bug1.m3", line 12: value is not constant
> "../src/bug1.m3", line 13: value is not constant
> 
> It works in C...
> 
> #include <stddef.h>
> 
> typedef struct { ptrdiff_t i, j;}T1;
> 
> T1 a;
> #define b ((T1*)0)
> T1* const c = &a;
> ptrdiff_t* const d = &a.i;
> ptrdiff_t* const e = &a.j;
> ptrdiff_t const f = offsetof(T1,j);
> ptrdiff_t* const g = &b->i;
> ptrdiff_t* const h = &b->j;
> ptrdiff_t const i = &b->j - (ptrdiff_t*)0;
> 
> 
> Thanks,
>  - Jay

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