On 1/17/2017 7:38 AM, somitcw wrote:
Does IBM plan to back-off the change from RXE to RXY and
go in a different direction or are they just sloppy about keeping
the first part of the manual insync with the rest?
According to Dan Greiner, the Principles of Operation is accurate and
IBM is neither being sloppy nor backing off any promised change. He writes:
"If one bothers to notice the heading under which [the cited text] appears:
* In Chapter 7, “General Instructions”:
– Thirty-nine instructions provided by the
long-displacement facility are added. With the exception of the
new LOAD BYTE instruction, the instructions added by the
long-displacement facility have names and functions that are the
same as existing instructions (but the mnemonics and opcodes are
new). The new instructions are of formats RSY, RXY, and SIY and have
a 20-bit signed displacement instead of a 12-bit unsigned displacement.
– All previously existing format-RSE and format-RXE
instructions are changed to be of formats RSY and RXY, respectively,
by use of a previously unused byte in the instructions. These
changes are not marked by a bar in the margin.
– Five instructions provided by the message-security
assist are added.
Thus, this statement regarding format-RSE and -RXE instructions applies
only to those in Chapter 7. A similar statement follows re: format-RSE
instructions in Chapter 10.
I wasn't involved in the initial design of long displacement, but as I
recall, there was much discussion as to whether there was a need to
extend the HFP and BFP instructions that access storage. Other than
adding long-displacement forms of LOAD (LEY, LDY) and STORE (STEY,
STDY), they decided against it. As you will have noticed with the newer
DFP and vector instructions, the vast majority are register-to-register
instructions; there are precious few that have storage operands. I
suspect this trend may have influenced the decision to not extend the
existing HFP and BFP operations to long-displacement forms."
--
Edward E Jaffe
Phoenix Software International, Inc
831 Parkview Drive North
El Segundo, CA 90245
http://www.phoenixsoftware.com/
