🚀 go-pugleaf

mcv@pi.net (Miguel Carrasquer Vidal) wrote:

>arlyn@airmail.net (Arlyn Chesley) wrote:

>>Need help with getting data onto and off of stacks

>#include <stdio.h>

>void stack_push(int);
>void stack_pop(void);
>/* warning: not ANSI C */
>void _pascal stack_push_bonus(int);

OK, so I mixed up my _pascal and _cdecl calling conventions.
It was 9 am and I was starting to get sleepy...

Technical and platform/implementation dependent explanation follows.  

C functions allow a variable number of arguments [<stdarg.h>, ...]
so the callee must know how to get to the _first_ parameter, and can't
know how to clean up the stack after itself.  On several PC compilers,
the caller therefore does (3-param example):

push param 3
push param 2
push param 1
call _cfunc
pop 3 params
...

_cfunc:
...

A Pascal function, on the other hand, knows exactly what it gets.
Caller simply does:

push param 1
push param 2
push param 3
call PFUNC
...

and the _pascal function does:

PFUNC:
...
pop 3 params
return

(actually that's a single i86 instruction: RET[F] <n_bytes_to_pop>)


==
Miguel Carrasquer Vidal                     ~ ~
Amsterdam                   _____________  ~ ~
mcv@pi.net                 |_____________|||

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