Threaded code: Difference between revisions

Revision as of 05:51, 21 April 2021

Revision as of 18:16, 20 May 2021

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===RPL===

[[Hewlett-Packard|HP]]'s [[RPL (programming language)|RPL]], first introduced in the [[HP-18C]] calculator in 1986, is a type of proprietary hybrid direct-threaded and indirect-threaded threaded-interpreted language that, unlike others TILs, allows embedding of RPL "objects" into the "runstream" ie. The stream of addresses through which the interpreter pointer advances. An RPL "object" can be thought of as a special data type whose in-memory structure contains an address to an "object prolog" at the start of the object, and then data or executable code follows. The object prolog determines how the object's body should be executed or processed. Using the "RPL inner loop",<ref name="RPL1">Busby, Jonathan. [https://www.hpmuseum.org/forum/thread-11358.html "The RPL inner loop explained"], [http://www.hpmuseum.org/ "The Museum of HP Calculators"], 7 September 2018, Retrieved on 27 December 2019</ref> which was invented and published ( and patented <ref>{{cite web | last = Wickes | first = William C. | title = Data processing system and method for the direct and indirect execution of uniformly structured object types | website = uspto.gov | date = May 30, 1986 | url = http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=8&p=1&f=G&l=50&d=PTXT&S1=((%22Hewlett+Packard%22.ASNM.)+AND+Wickes.INNM.)&OS=AN/%22Hewlett+Packard%22+and+IN/Wickes&RS=(AN/%22Hewlett+Packard%22+AND+IN/Wickes) | access-date = December 27, 2019 }}</ref> ) by William C. Wickes in 1986 and published in "Programming Environments", Institute for Applied Forth Research, Inc., 1988, execution follows like so :

# Dereference the IP ( instruction pointer ) and store it into O ( current object pointer )

# Increment IP by the length of one address pointer

# Dereference O and store its address in O_1 ( This is the second level of indirection )

# Transfer control to next pointer or embedded object by setting the PC ( program counter) to O_1 plus one address pointer

# Go back to step 1

This can represented more precisely by :

<pre>

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Where above, O is the current object pointer, I is the interpreter pointer, Δ is the length of one address word and the "[]" operator stands for "dereference".

When control is transferred to an object pointer or an embedded object, execution continues as follows :

<pre>