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Indirection | 134 comments | Create New Account
Comments belong to whoever posts them. Please notify us of inappropriate comments.
Indirection
Authored by: bugstomper on Monday, May 14 2012 @ 04:52 AM EDT
"If there is any suggestion that the patent covers indirect indexing in any
way, then this is completely wrong"

You may have got that from my poor phrasing in a comment. I didn't mean that
there is an interpretation of the claims that would mean that use of indirect
indexing itself is covered by the patent.

To rephrase it more clearly: Some of the testimony made it seem as if the claims
were being interpreted as covering only instructions that include the actual
symbol being used in the reference, as in an instruction LOAD "y". But
there is indication that the claims would also apply to an instruction that
contains an indexed reference or other indirect reference to the symbol. It's
hard to say that without it sounding like "the claim covers indirect
indexing". The claim does not fail to cover what it covers just because the
instruction uses an indirect reference.

[ Reply to This | Parent | # ]

  • Indirection - Authored by: Anonymous on Monday, May 14 2012 @ 11:04 AM EDT
Indirection
Authored by: ThrPilgrim on Monday, May 14 2012 @ 06:21 AM EDT
The Z80 had indirection.

You could write assembly code like

INC (IX+10)

or even

LD (IY+23), 'A'

As the IX and IY registers where the index registers.

---
Beware of him who would deny you access to information for in his heart he
considers himself your master.

[ Reply to This | Parent | # ]

Indirection
Authored by: IANALitj on Monday, May 14 2012 @ 10:45 AM EDT
Indirection was built into the large IBM "scientific" computers of the
1950s and 1960s, the 704 and its successors. (These were also known as the
PQ-bit machines; in addition to the 36 bits, including sign, of a memory word,
the accumulator register had additional bits referred to as P and Q.)

Many instructions that had their operand in memory had bits 12 and 13 set aside,
known as the "flag" bits. When both of these bits were set, indirect
addressing applied (at the cost of only one additional machine cycle). This was
indicated in the assemblers by an asterisk.

My recollection is that only one level of indirection was allowed.

[ Reply to This | Parent | # ]

Indirection
Authored by: jesse on Monday, May 14 2012 @ 11:37 AM EDT
Those machines that did not implement indirection in hardware had an alternative
- index registers.

This required the software to load an index register with the address of the
data desired, then retrieve the value indirectly through the index registers.

[ Reply to This | Parent | # ]

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