Extremely CISC instructions
cube1 at charter.net
Tue Aug 24 16:11:57 CDT 2021
On 8/23/2021 8:51 PM, Van Snyder via cctech wrote:
> On Tue, 2021-08-24 at 01:38 +0100, Tom Stepleton via cctalk wrote:
>> For the sake of illustration to folks who are not necessarily used to
>> thinking about what computers do at the machine code level, I'm
>> in collecting examples of single instructions for any CPU
>> architecture that
>> are unusually prolific in one way or another.
> IBM 1401 was a character-by-character machine, so most operations had
> costs proportional to field length.
> One especially expensive (but very useful) operation was "move
> characters and edit."
> Assuming a 17-character control word has been loaded to the
> destination, e.g.
> "$ , 0. &CR&**"
> to edit a data field "00257426" with a "negative" zone bit on the low-
> order digit, producing
> "$ 2,574.26 CR **"
> requires 41 memory accesses (including seven to fetch the instruction)
> -- 0.4715 milliseconds.
> See pages 41-43
> at http://www.bitsavers.org/pdf/ibm/1401/A24-1403-5_1401_Reference_Apr62.pdf
> On a machine where the "Expanded Print Edit Feature" was added, the
> instruction cost even more. For example, the "Floating Dollar Sign"
> moves the dollar sign to immediately to the left of the most
> significant digit. This (and asterisk protection) was to prevent
> somebody from adding digits between a left-justified dollar sign and
> leading digits on printed checks. The above edit would cost two more
> memory cycles. If the datum had had more leading zeroes, even more
> cycles would have been required.
Useful for COBOL. ;)
> See pages 82-84.
> Another expensive instruction was the simpler "move characters and
> suppress zeros" instruction. See page 38.
Along those same lines, the IBM 1410 had what the 1401 had, plus:
- A very useful table lookup instruction (pp 29-31)
- At least 56 ways to move data, depending upon the "d" character
(op modifier) specified (pp 25-28)
- A scan that could stop at various terminators without moving data
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