Re: Overflow errors on add

Eric wrote:
>     There is a command line option TRUNCNBR in the CRTBNDRPG command.
>     This will cause overflow values to be truncated. This doesn't work
>     on calculations performed within expressions (eval and other
>     opcodes that us the extended factor 2 field). In cases where you
>     know you'll have an overflow occur, just go back to the standard
>     math ops in place of the expression calcs.

Also, TRUNCNBR does not apply to any of the non-decimal
numeric datatype: integer, unsigned, and float.  TRUNCNBR
applies only to the decimal datatypes (packed, zoned, and
binary) and only on the old-style fixed format opcodes.

Considering the risks involved with TRUNCNBR(*YES),
perhaps programmers should use conversion to RPG IV as an
opportunity to redo their numeric operations that rely on
truncation.  Since very few calculations really need to
take advantage of truncation, running with TRUNCNBR(*NO)
can help you ensure that your calculations produce
correct results.  For the very few cases where truncation
is needed, there are alternatives, such as MVR or even
MOVE.

One place where truncation is sometimes justified is to
compute the remainder after division by some multiple of
10 in order to compute a hash index.  While this is
certainly easy, it is a very poor way to implement a hash
table.  Hash tables work best when the hash table size is
a prime number.

My bottom line recommendation is this:  Run your RPG
programs with TRUNCNBR(*NO).  If you get the numeric
overflow exception, determine why.  If it's a bug, fix it.
If not, recode the computation and use MOVE or MVR to
perform the truncation.

Cheers!  Hans

Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com
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