C-code translated to assembler

dissident · Yesterday, 21:16

I understannd much of C code, but not all.

While I tried to use the gadtools.library, I stumbled over this:

Code:

struct Gadget *glist = NULL;
gad = CreateContext(&glist);

A pointer to a gadget structure should be set to NULL!?

How does the similar code look in assmbler? Like this?

Code:

  lea glist(pc),a0
  clr.l (a0)
  CALLGADTOOLS CreateContext

glist
  DS.B gg_SIZEOF

Or only

Code:

  sub.l a0,a0
  CALLGADTOOLS CreateContext

I don't get it.

thomas · Yesterday, 21:35

The first snippet is correct.

glist should be ds.l 1 for proper alignment. Or dc.l 0, then you don't need the clr.l (a0).

Samurai_Crow · Yesterday, 21:36

Globals are set to 0 or null at startup due to being initialized with MEMF_CLEAR but the NULL assignment is just making sure there is no phantom data in memory. The assignment should reduce out to nothing.

a/b · Yesterday, 21:39

It's a pointer to pointer, so it's the former (NULL is overwritten with a valid pointer on return, if successful). Passing a0=0 would be equivalent to CreateContext(NULL) and result in address 0 being trashed ("NULL ptr problem").

dissident · Yesterday, 22:08

Thx for your quick replies. Now I understand it much better.

Yesterday, 21:16	#1
dissident Registered User Join Date: Sep 2015 Location: Germany Posts: 276	C-code translated to assembler I understannd much of C code, but not all. While I tried to use the gadtools.library, I stumbled over this: Code: struct Gadget glist = NULL; gad = CreateContext(&glist); A pointer to a gadget structure should be set to NULL!? How does the similar code look in assmbler? Like this? Code: lea glist(pc),a0 clr.l (a0) CALLGADTOOLS CreateContext glist DS.B gg_SIZEOF Or only Code: sub.l a0,a0 CALLGADTOOLS CreateContext I don't get it. Last edited by dissident; Yesterday at 21:23.*

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Yesterday, 21:35	#2
thomas Registered User Join Date: Jan 2002 Location: Germany Posts: 7,047	The first snippet is correct. glist should be ds.l 1 for proper alignment. Or dc.l 0, then you don't need the clr.l (a0).

Yesterday, 21:36	#3
Samurai_Crow Total Chaos forever! Join Date: Aug 2007 Location: Waterville, MN, USA Age: 49 Posts: 2,224	Globals are set to 0 or null at startup due to being initialized with MEMF_CLEAR but the NULL assignment is just making sure there is no phantom data in memory. The assignment should reduce out to nothing.

Yesterday, 21:39	#4
a/b Registered User Join Date: Jun 2016 Location: europe Posts: 1,093	It's a pointer to pointer, so it's the former (NULL is overwritten with a valid pointer on return, if successful). Passing a0=0 would be equivalent to CreateContext(NULL) and result in address 0 being trashed ("NULL ptr problem").

Yesterday, 22:08	#5
dissident Registered User Join Date: Sep 2015 Location: Germany Posts: 276	Thx for your quick replies. Now I understand it much better.

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