Re: Compute Date Duration

OK. Here's what some experimentation shows:

CDD will calculate a duration between character format dates. This is 
consistent with the CDD instruction description which states that 
operands 2 and 3 must be character scalars. That means the only valid 
date types for operands 2 and 3 are:
	USA
	ISO
	EUR
	JIS
	System Internal Date (Scaliger number)
	*MMDDYY
	*DDMMYY
	*YYMMDD
	*YYDD
	*YYYYDDD

Default separators are required for the first 5 but the last 5 can have 
any separator or no separator as long as the DDAT correctly describes 
the separator. If the specified date value does not match the DDAT then 
MCH1222 will occur.

NOTE:- The scaliger number specified for the System Internal Date type 
must not exceed the end date of the Calendar (else MCH1221) nor must it 
be earlier than the start date of the Calendar (else MCH1224).

CDD does not support other date formats so if you have dates in other 
formats (e.g. packed or zoned numeric) you must first convert them to a 
format that CDD does support.

Most DDAT errors will cause MCH1867 but some will cause MCH5601. Errors 
in the first 58 bytes of the template will cause MCH5601.

CDD always returns a Date Duration. That is an 8,0 packed decimal value 
in the form YYYYMMDD which is interpreted as YYYY years, MM months, and 
DD days. Specifying any other format type will result in MCH5601.

I also discovered that if the Calendar Table is not allowed for a 
particular format type (such as Date Duration) then if you specify zero 
for the Calendar Offset you can omit the Calendar Table entirely.

However the Era Table must be present (and set to X'00' for a Date 
Duration) otherwise MCH1867 is sent with reason code 19

Further the DDAT_List_Size (as distinct from the DDAT_Length which can 
be anything including zero) is validated for being greater than 0 but 
otherwise seems to tolerate incorrect values. Not that I'm advocating 
doing so but it is interesting. When it is zero the #cfdate module gets 
the DDAT number wrong in MCH1867. It shows 16448 which is the value of 
an uninitialised BIN(2).

So that just leaves the question of how to convert a Date Duration to a 
Labelled Duration and that can be done with maths.

I haven't found an MI instruction that will generate a Labelled 
Duration. They seem to be valid only as input to the various INC and 
DEC instructions.

Regards,
Simon Coulter.
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