> Now a question on COBOL:
>
> 77 var8 PIC 999V9(8) COMP-5
>
> what precision/digits does this specify? When then doing
>
> add 0.00000001 TO var555 giving var8 rounded
>
> what's the precision/digit specification for the literal floating
> point values and how does that or that of var555 or var8
> "promote" or "demote" to a common specification for the arithmetic
> operation?
>
> Does the COBOL standard expect a literal floating point value to
> be represented exactly? Maybe rounding then only applies at the
> "giving var8 rounded" point, forcing the exact value to the
> specification of var8?
>
> Richard.
That's NOT a floating-point in COBOL, but a fixed-point numeric literal.
It is best understood with the following explanation from the standard:
> An integer literal is a fixed-point numeric literal that contains no
decimal point.
--> it is to be used as integer with an implied decimal point after the
first position, as if it would be defined with a PIC 9v99999999
floating-point literals in COBOL would have the following most important
difference:
> A floating-point numeric literal is formed from two fixed-point
numeric literals separated by the letter 'E' without intervening spaces.
The requested *minimal* precision - "stored exactly" is:
* 31 digits for fixed-point numeric literals (and effectively all
calculations with those, before rounding/truncation applies)
* up to 36 digits of significand with up to 4 digits in exponent for
floating-point literals
Back to your arithmetic question: COBOL standard expects that to be
exact for an intermediate value up to these sizes.
If the sizes get bigger and cannot be stored (the maximum is
implementor-defined = "should be documented in the user-documentation")
then there's the option to specify which INTERMEDIATE ROUNDING should
apply (= per program), which includes ROUNDING/TRUNCATION/PROHIBITED
(=an exception raised).
The default for INTERMEDIATE ROUNDING dependens on which arithmetic is
in effect (also per program defined, NATIVE is default where rounding is
implementor-defined, STANDARD-BINARY and STANDARD-DECIMAL can be chosen).
> If the NATIVE phrase is specified [or implied], the techniques used
in handling arithmetic expressions and intrinsic functions shall be
those specified by the implementor, [as well as] the techniques used in
handling arithmetic statements [mostly for rounding/truncation].
--> note that STANDARD-DECIMAL arithmetic is no optional feature, so for
full compliance that has to be considered - but can also be "ignored in
detail" for now; note that the OPTIONS paragraph (support for the
paragraph is required since COBOL2002) is only supported by GnuCOBOL
(neither IBM nor Micro Focus nor Fujitsu support it and all go with
"native arithmetic" only).
also mind that COBOL2014 has a note:
> Implementors are strongly encouraged to provide support for the
STANDARD-DECIMAL phrase of the ARITHMETIC clause
... sorry for another "background-drift", getting to your question again:
* intermediate values need to cover at least the sizes outlined above
* for bigger sizes truncation/rounding may apply - the rules that IBM,
MF and GnuCOBOL applies are different (with GnuCOBOL being nearly
infinite using GMP with an internal scale as intermediate
representation)
* the truncation/rounding that applies for a statement can be specified
at the statement (as in your example where "rounded" only applies to
this final "store to the receiving item") with the default being able
to be configured in the OPTIONS paragraph "DEFAULT ROUNDED MODE"
Hope this helps with some background and answers your questions,
Simon
