To avoid the problem Dan illustrates but retain the advantages Charles
cites of not labeling specific instructions, we use
label DS 0H instead of label EQU *
But i think some of the point of the original post was lost, since the
question was whether
label EQU *
was ever beneficial, where the "*" indicates current location rather
than meaning generically any value.
On 2018-08-01 2:23 PM, Dan Greiner wrote:
I too disagree (rather strongly).
As an example, consider where EQU is used to give names to bits of a field in
memory.
FLAGS DS X
F_OPEN EQU X'80'
F_CLOSE EQU X'40'
F_FUBAR EQU X'20'
...
TM FLAGS,F_FUBAR
JO TOTALLY_HOSED
Furthermore, you can assign a "length" to each bit, and use that as an offset
in the field, e.g:
FLAGS DS XL4
F_OPEN EQU X'80',0
F_CLOSE EQU X'40',0
F_FUBAR EQU X'02',3
...
TM FLAGS+L'F_FUBAR,F_FUBAR
(apologies if the syntax is not precise ... I'm doing this from memory at home).
As to Charles' comment about using EQU as a branch target, I'm a little bit
less comfortable. If — by chance or accident — there happens to be code before
the EQU that knocks the location off a halfword boundary, this could spell
trouble. E.g:
LA 7,ITS_ON
TM BYTE,BIT
BCR X'01',7
...
other instructions
HI_MOM DC C'Hello'
ITS_ON EQU *
Since the constant "Hello" is 5 bytes long, this knocks the label ITS_ON onto
an odd boundary. If the branch had been directly to the location (as opposed to BCR),
HLASM would have flagged an error. But in this case, the error may go undetected until
execution — at which point the hardware will slap you with a PIC-0006 (PIC-0006).
Gary Weinhold
Senior Application Architect
DATAKINETICS | Data Performance & Optimization
Phone +1.613.523.5500 x216
Email: weinh...@dkl.com
Visit us online at www.DKL.com
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