In <[EMAIL PROTECTED]>, on 11/02/2006
at 03:39 AM, Chris Mason <[EMAIL PROTECTED]> said:
>It seems reasonable that the field M1CC is defined as having length
>5. If not, the programming is a mess. If so, the "L'M1CC+1"
>specification is stupid.
No.
>It's stupid because the expression already indicates the length by
>virtue of having included the literal
The assembler takes the length from the first operand, not from the
second. That's why you'll sometimes see a CLC with a literal as the
first operand.
>In fact the "print hexadecimal" case is even trickier that the
>"print decimal" case since, in the letter case, all the instructions
>were doing precisely what the Principles of Operation says they do
Likewise in the former case.
>The "unpack" instruction makes what is, in fact, an incorrect
>assumption.
Not really; it is doing exactly what PoOps says it does.
>[1] In fact the "packed decimal standard", as it were, allows some
>flexibility in the hexadecimal digit which forms the, so-called,
>"sign half-byte".
Not very much.
>I forget every last detail but it may be as simple as only the
>lowest bit being significant
It isn't. Only specific values are allowed as a sign.
>Suffice to say that it was once proposed that the "Add Register"
>instruction code, X'1A', could be used as a positive packed
>decimal "1"
Perhaps in ASCII mode, which no longer exists. Certainly not in EBCDIC
mode.
--
Shmuel (Seymour J.) Metz, SysProg and JOAT
ISO position; see <http://patriot.net/~shmuel/resume/brief.html>
We don't care. We don't have to care, we're Congress.
(S877: The Shut up and Eat Your spam act of 2003)
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