01 sixteen-pd pic 9(16) packed-decimal.
01 binaries usage binary.
05 bin-var-1 pic s99.
05 bin-var-2 pic 9(6).
05 bin-var-3 pic s9(4).
05 bin-var-4 pic s9(9).
[...]
move zeroes to bin-var-1
move 123451 to bin-var-2
sixteen-pd
display bin-var-1 space bin-var-2
move bin-var-2 to bin-var-1
display bin-var-1 space bin-var-2
move sixteen-pd to bin-var-1
display bin-var-1 space bin-var-2
move zeroes to bin-var-3
move 123451 to bin-var-4
sixteen-pd
display bin-var-3 space bin-var-4
move bin-var-4 to bin-var-3
display bin-var-3 space bin-var-4
move sixteen-pd to bin-var-3
display bin-var-3 space bin-var-4
exit.
TRUNC(STD) results
+00 123451
+51 123451
+51 123451
+0000 +000123451
+3451 +000123451
+3451 +000123451
TRUNC(OPT) results
+00 123451
-21 123451
+51 123451
+0000 +000123451
-7621 +000123451
+3451 +000123451
________________________________
From: Steve Comstock <[email protected]>
To: [email protected]
Sent: Friday, September 26, 2014 12:06 PM
Subject: Re: COBOL 5 compile options
On 9/26/2014 11:31 AM, Frank Swarbrick wrote:
I've been pondering the TRUNC option since yesterday. Let me ask
thisquestion... Is the only time the TRUNC option come in to effect
when one binary field is moved to another, smaller, binary field?
Because it appears if a packed-decimal or zoned decimal field is
moved in to a smaller binary field the TRUNC(STD) logic is always
performed. Specifically, the sending field is moved to a temp
field,
it is then truncated, and then converted to binary. At least in the
examples I've tried.
TRUNC(STD) indicates to the compiler that results of MOVEs or
calculations into BINARY fields should be truncated to the precision
of the PICTURE (this conforms to ANSI standards)
Consider:
05 FLDA PIC S99 COMP.
if you code MOVE +125 TO FLDA the result should be '25'
(x'0019') in FLDA - truncation to the number of 9's in the picture -
with TRUNC(STD).
With TRUNC(BIN) the result is '125' (x'007D') - the whole result is
included as long as it fits into physical size (halfword in this case)
of the target field.
With TRUNC(OPT) the compiler will choose the instruction path that is
fastest; might be a MVC, might be LH / STH, etc.; it
depends. IBM has never documented the rules, claiming they are
'proprietary' or at least subject to change from release to release.
Recommend: binary fields should be defined with the maximimum number
of nines (such as PIC S9999 for halfword) and compile with TRUNC(OPT).
-Steve Comstock
If that's the case I think I'll just stay with TRUNC(STD) since
situations where TRUNC(OPT) would come in to play would be rare
enough anyway that there would be no noticeable gain, and too much to
lose. I can't think of many cases where someone would
move a "large" binary field to a smaller one anyway.
Personally, I think "picture defined" COMP/BINARY fields should be
eliminated in favor of the COBOL 2002 BINARY-SHORT (halfword),
BINARY-LONG (fullword) and BINARY-DOUBLE (doubleword) data types,
which make much more sense in the real world anyway. (of course
eliminating the legacy data types is never going to happen, because
its too ingrained.)
Thanks,
Frank
________________________________
From: Tom Ross <[email protected]>
To: [email protected]
Sent: Friday, September 26, 2014 10:51 AM
Subject: Re: COBOL 5 compile options
Thanks Tom!
For HGPR, don't you mean the reverse of what you said? PRESERVE
would alwa= ys be save because COBOL preserves and restores the
high-halves of the regi= sters, right? Safer, but not as efficient?
Ooops, at least I was 100% wrong :-) Yes, PRESERVE is safer,
although NOPRESERVE might be safe for most as well.
As for NUMPROC, thanks for the info. Seems to me the documentation
could b= e made clearer, though I don't know exactly all. In the
end I can't imagin= e doing what you suggest, even though "it's the
only way to be sure". So w= e'll probably, unfortunately, just go
with NOPFD. But thanks a lot for the= info!!
Yes, I was aware that my idea was kind of crazy, and eve asked at
SHARE if anyone
could ever do such a thing. On the other hand, if you did not find
out
if your data has preferred signed and chose PFD, you could get silent
death ;-)
Question about one additional option. We use TRUNC(STD) right now.
What w= ould be have to be aware of if we wanted to switch to
TRUNC(OPT) (where I a= ssume OPT =3D "optimize")? Is OPT fully
compliant with COBOL standard trun= cation rules?
TRUNC(OPT) does not result in any code generated to truncate. it is
NOT COBOL Standard conforming and neither is TRUNC(BIN). You could
get more accurate results with TRUNC(OPT) (along with much better
performance) but I know that for many customers 'more accurate' =
'different' = BAD :-)
Cheers,
TomR >> COBOL is the Language of the Future! <<
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