Am 21.12.2013 16:06, schrieb Paul Gilmartin:
On 2013-12-21, at 05:51, John Gilmore wrote:
EJ's macro can of course be written in the form
MACRO ,
&LABEL DIAG &R1,&R2,&I1
&LABEL LA &R1,&I1.(&R2.,0) Diagnose
ORG &LABEL
DC X'83'
ORG ,
MEXIT ,
MEND ,
and this form, which delegates the location-counter arithmetic to the
assembler, seems to me to be at once clearer and less error-prone.
Agreed.
The first ORG only does what it is supposed to do,
if there is a label on the macro call, and so the ORG *-4
which EJ provided in his original version is better.
Dijkstra's epigoni have conditioned many people to avoid the use of
labels whenever possible, even at the expense of real ugliness, not
present here; but the use of an already present label in this way
seems to me to be entirely benign. Moreover, their judicious use
often makes it possible to avoid what Tony Harminc has just called
"fancier ORGs".
Agreed. But the ORG without argument may not do what you desire:
It sets the location counter to the previous highwater mark, which
may, because of prior ORGs, be elsewhere than the end of the LA.
The second ORG indeed is subject to the problem you described,
so, again, the version that EJ originally provided (ORG *+3), is better.
Inside macros, there are different rules for good, bad and ugly code.
-- gil
