Cody Boone Ferguson
41abeda97a
In the line in README.md and index.html files that said:
### NOTICE to those who wish for a greater challenge
I added a ':' at the end of the line.
There were some entries that had a link fix in the index.html file but I
only looked up through 1995/leo as those still have to have a 'look and
feel' check and it would just slow things down.
94 lines
2.9 KiB
Markdown
94 lines
2.9 KiB
Markdown
### NOTICE to those who wish for a greater challenge:
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**If you want a greater challenge, don't read any further**:
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just try to understand the program via the source.
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If you get stuck, come back and read below for additional hints and information.
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# Obfuscation
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The program implements a so called [Krivine
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machine](https://en.wikipedia.org/wiki/Krivine_machine), enhanced with a [basic
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input/output system](https://en.wikipedia.org/wiki/BIOS) and a reference
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counting [garbage collector](https://en.wikipedia.org/wiki/Waste_collector). The
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Krivine machine is a stepwise transformer of a global state consisting of the
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current term, the current environment (a list of closures), and a stack of
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continuations (see the 3rd reference for details).
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The term space holds [lambda
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calculus](https://en.wikipedia.org/wiki/Lambda_calculus) terms in the following
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format. 0 denotes some form of I/O; the only four occurrences are at:
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```
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C=13: recognizes end of a byte
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C=20: recognize output of 0 bit
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C=21: recognize output of 1 bit
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C=end: input list, expanded lazily
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```
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`1` denotes a variable, with the next entry its [de Bruijn
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index](https://en.wikipedia.org/wiki/De_Bruijn_index).
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`2` denotes application with the next entry the size of the term being applied.
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`3` denotes lambda abstraction.
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A closure consists of the following items:
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0. pointer to the next closure (as part of an environment), or next record on
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free list.
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1. reference count.
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2. pointer to environment.
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3. lambda term (index in term space).
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Here's what each variable does:
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```
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L Lambda term space
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m mode: 0 for bits and 7 for bytes
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b bits remaining unread in I, -1 on EOF
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D Desirable temporary
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c continuation context
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a active environment pointer
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C Current term index
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U Ultimate term pointer
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u utility entry
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B Born to be free-list of closures
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I Input character
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O Output character
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e entry of current term
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```
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Here's what each of the 6 auxiliary functions do:
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```
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s variable lookup in active environment with de Bruijn index u
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S gets one bit of input, setting b to -1 on EOF or to remaining number of bits in current byte
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k copy fragment from string literal holding lambda terms xor 46 into current end of term space
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x expand input, adding 11 (resp. 99) entries to term space for bit (resp. byte) mode
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p parses BLC-encoded lambda term using S(), stores results in term space and returns length
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d decrease reference counter, add record to free list on reaching zero
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```
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<hr style="width:10%;text-align:left;margin-left:0">
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Jump to: [top](#)
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<!--
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Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
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You are free to share and adapt this file under the terms of this license:
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Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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For more information, see:
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
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