Re: XCAR/XCDR as lvalues

Friday, 22 January 1999

        Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes:

...
 Yes [I'll reread again to be sure]. You mean

 #define XSETCAR(conscell, newcar) do {
   CHECK_IMPURE (conscell);
   XCAR (conscell) = newcar;
 } while (0) 
Yes.

...
 int
 purified (Lisp_Object obj)
 {
   return POINTER_TYPE_P (XGCTYPE (obj)) && PURIFIED (XPNTR (obj));
 } 
I'll trivially recode this as a macro.

...
 i.e. you might have eliminated the call to Fsetcar, but there is
still 
 a function call involved. Note that the 'PURIFIED' macro ALSO involves 
 a function call. However that one will be hopefully be inlined when
 compiled at -O3 
It won't, because the function definition is in another file.
However, I can recode that as a macro too.

...
 So I think if you want to go that way, you should at the very least
 eliminate the function calls from all those macros. Also the
 POINTER_TYPE_P (XGCTYPE (obj) check is completely unneeded in
 XSETCAR. 
Yup.  I might make a CHECK_IMPURE_UNSAFE macro or something; I'll
think about it.  Thanks for the tips.

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