Re: Odd, inconsistent rounding error

Hi James,

normally, you should’ve have rounding issues with ADD|+ or MULT|* operations.

When it comes to EVAL there are rules for the intermediate results before they are „moved“ into the result field.

https://www.ibm.com/docs/en/i/7.3?topic=expressions-precision-rules-numeric-operations

This differs between EVAL and ADD/MULT/DIV/SUB opcodes. EVAL creates large temporary intermediate result fields and tries not to loose any precision during the right-side evaluation.

Whereas ADD/MULT always cut/round the result to the precision of the given result field for every step of the sequence of operations.

But in your case, one of the problems seems to be U01168 which is 11,2 where all other fields are nn,5. Whenever you assign a value to this field, the precision is reduced to 11,2 - and in you case without rounding.

HTH
Daniel

Am 28.07.2023 um 01:10 schrieb James H. H. Lampert via RPG400-L <rpg400-l@xxxxxxxxxxxxxxxxxx>:

I've got some strange rounding behavior:

Given the following fields:

DIQTSH is zoned 15.5, in a file
DIPRIC is zoned 12.5, in a file
K01108 is zoned 12.5, defined in a standalone D-spec
U01107 is zoned 15.5, in a file
U01108 is zoned 12.5, in a file
U01168 is zoned 11.2, in a file
AMOUNT is packed 15.5, defined in a C-spec


The existing program has:
eval u01108 = u01108 * u01107
eval U01168 = U01168 + U01108

while my program has:
DIQTSH MULT K01108 AMOUNT
and either
ADD AMOUNT U01168
or
EVAL U01168 = U01168 + AMOUNT

K01108 and U01108 both come from DIPRIC. U01107 comes from DIQTSH.

My code should be equivalent to the exiting code, and yet in 12 out of 30669 cases, U01168 is off by a few cents between the two.

Anybody else have any insights into this? I tried replacing the ADD with the EVAL, with no effect on the output.

--
JHHL
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