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Malbolge

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This article is about the programming language. For the eighth circle of hell in Dante's Inferno, see Malebolge.
Malbolge
ParadigmEsoteric, Imperative, Scalar, Value-level
Designed byBen Olmstead
First appeared1998
Typing disciplineUntyped
Filename extensions.mal, .mb
Influenced by
Brainfuck, INTERCAL (Tri-INTERCAL), Befunge
Influenced
Dis

Malbolge is a public domain esoteric programming language invented by Ben Olmstead in 1998, named after the eighth circle of hell in Dante's Inferno, the Malebolge.

Malbolge was specifically designed to be almost impossible to use, via a counter-intuitive 'crazy operation', base-three arithmetic, and self-altering code.[1] It builds on the difficulty of earlier, challenging esoteric languages (such as Brainfuck and Befunge), but takes this aspect to the extreme, playing on the entangled histories of computer science and encryption. Despite this design, it is possible (though very difficult) to write useful Malbolge programs.

Programming in Malbolge

Malbolge was so difficult to understand when it arrived that it took two years for the first Malbolge program to appear. Indeed, the author himself has never written a single Malbolge program.[1] The first program was not written by a human being: it was generated by a beam search algorithm designed by Andrew Cooke and implemented in Lisp.[2]

Later, Lou Scheffer posted a cryptanalysis of Malbolge and provided a program to copy its input to its output.[3] He also saved the original interpreter and specification after the original site stopped functioning, and offered a general strategy of writing programs in Malbolge as well as some thoughts on its Turing-completeness.[4]

Olmstead believed Malbolge to be a linear bounded automaton. There is a discussion about whether one can implement sensible loops in Malbolge — it took many years before the first non-terminating one was introduced. A correct 99 Bottles of Beer program, which deals with non-trivial loops and conditions, was not announced for seven years; the first correct one was by Hisashi Iizawa in 2005.[5] Hisashi Iizawa et al. also proposed a guide for programming in Malbolge for the purpose of the application for obfuscation in software protection.[6]

Example Program

Hello, World!

This Malbolge program displays "Hello World!", with both words capitalized and exclamation mark at the end. 

 (=<`#9]~6ZY32Vx/4Rs+0No-&Jk)"Fh}|Bcy?`=*z]Kw%oG4UUS0/@-ejc(:'8dc

CAT Program

This program reads a string from a user and prints that string. 

(aBA@?>=<;:9876543210/.-,JH)('&%$#"!~}|{zy\J6utsrq
ponmlkjihgJ%dcba`_^]\[ZYXWVUTSRQPONMLKJIHGF('C%$$^
K~<;4987654321a/.-,\*)
j
!~%|{zya}|{zyxwvutsrqSonmlO
jLhg`edcba`_^]\[ZYXWV8TSRQ4
ONM/KJIBGFE>CBA@?>=<;{9876w
43210/.-m+*)('&%$#"!~}|{zy\
wvunslqponmlkjihgfedcEa`_^A
\>ZYXWPUTSRQPONMLKJIH*FEDC&
A@?>=<;:9876543210/.-m+*)(i
&%$#"!~}|{zyxwvutsrqpRnmlkN
ihgfedcba`_^]\[ZYXWVU7SRQP3
NMLKJIHGFEDCBA@?>=<;:z8765v
3210/.-,+*)('&%$#"!~}_{zyx[
vutsrqjonmlejihgfedcba`_^]@
[ZYXWVUTSRo

Design

Malbolge is machine language for a ternary virtual machine, the Malbolge interpreter.

The standard interpreter and the official specification do not match perfectly.[7] One difference is that the compiler stops execution with data outside the 33–126 range. Although this was initially considered a bug in the compiler, Ben Olmstead stated that it was intended and there was in fact "a bug in the specification."[1]

Registers

Malbolge has three registers, a, c, and d. When a program starts, the value of all three registers is zero.

a stands for 'accumulator', set to the value written by all write operations on memory and used for Standard I/O. c, the code pointer, is special: it points to the current instruction.[8] d is the data pointer. It is automatically incremented after each instruction, but the location it points to is used for the data manipulation commands.

Pointer notation

d can hold a memory address; [d] is the value stored at that address. [c] is similar.

Memory

The virtual machine has 59049 (310) memory locations that can each hold a ten-trit ternary number. Each memory location has an address from 0 to 59048 and can hold a value from 0 to 59048. Incrementing past this limit wraps back to zero.

The language uses the same memory space for both data and instructions. This was influenced by how hardware such as x86 architecture worked.[1]

Before a Malbolge program starts, the first part of memory is filled with the program. All whitespace in the program is ignored and, to make programming more difficult, everything else in the program must start out as one of the instructions below.

The rest of memory is filled by using the crazy operation (see below) on the previous two addresses ([m] = crz [m - 2], [m - 1]). Memory filled this way will repeat every twelve addresses (the individual ternary digits will repeat every three or four addresses, so a group of ternary digits is guaranteed to repeat every twelve).

Instructions

Malbolge has eight instructions. Malbolge figures out which instruction to execute by taking the value [c], adding the value of c to it, and taking the remainder when this is divided by 94. The final result tells the interpreter what to do:

Instructions
Value of
([c] + c) % 94		 Instruction
represented		 Explanation
4 jmp [d] The value at [d] is where Malbolge will jump to and start executing instructions.
5 out a Prints the value of a, as an ASCII character, to the screen.
23 in a Inputs a character, as an ASCII code, into a. Newlines or line feeds are both code 10. An end-of-file condition is code 59048.
39 rotr [d]
mov a, [d]		 Rotates the value at [d] by one ternary digit (0002111112 becomes 2000211111). Stores the result both at [d] and in a.
40 mov d, [d] Copies the value at [d] to d.
62 crz [d], a
mov a, [d]		 Does the crazy operation (see below) with the value at [d] and the value of a. Stores the result both at [d] and in a.
68 nop Does nothing.
81 end Ends the Malbolge program.
Any other value does the same as 68: nothing. These other values are not allowed in a program while it is being loaded, but are allowed afterwards.

After each instruction is executed, the guilty instruction gets encrypted (see below) so that it won't do the same thing next time, unless a jump just happened. Right after a jump, Malbolge will encrypt the innocent instruction just prior to the one it jumped to instead. Then, the values of both c and d are increased by one and the next instruction is executed.

Crazy operation

For each ternary digit of both inputs, use the following table to get a ternary digit of the result. For example, crz 0001112220, 0120120120 gives 1001022211.

Crazy operation[1][6]
crz Input 2
0 1 2
Input 1 0 1 0 0
1 1 0 2
2 2 2 1

Encryption

After an instruction is executed, the value at [c] (without anything added to it) will be replaced with itself mod 94. Then, the result is encrypted with one of the following two equivalent methods.

Method 1
Find the result below. Store the ASCII code of the character below it at [c].
0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999
0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123
----------------------------------------------------------------------------------------------
9m<.TVac`uY*MK'X~xDl}REokN:#?G"i@5z]&gqtyfr$(we4{WP)H-Zn,[%\3dL+Q;>U!pJS72FhOA1CB6v^=I_0/8|jsb
Method 2
Find the result below. Store the encrypted version at [c].
Encryption table
Result Encrypted Result Encrypted Result Encrypted Result Encrypted Result Encrypted
0 57 19 108 38 113 57 91 76 79
1 109 20 125 39 116 58 37 77 65
2 60 21 82 40 121 59 92 78 49
3 46 22 69 41 102 60 51 79 67
4 84 23 111 42 114 61 100 80 66
5 86 24 107 43 36 62 76 81 54
6 97 25 78 44 40 63 43 82 118
7 99 26 58 45 119 64 81 83 94
8 96 27 35 46 101 65 59 84 61
9 117 28 63 47 52 66 62 85 73
10 89 29 71 48 123 67 85 86 95
11 42 30 34 49 87 68 33 87 48
12 77 31 105 50 80 69 112 88 47
13 75 32 64 51 41 70 74 89 56
14 39 33 53 52 72 71 83 90 124
15 88 34 122 53 45 72 55 91 106
16 126 35 93 54 90 73 50 92 115
17 120 36 38 55 110 74 70 93 98
18 68 37 103 56 44 75 104

Lou Scheffer's cryptanalysis of Malbolge mentions six different cycles in the encryption. They are listed here:

  • 33 ⇒ 53 ⇒ 45 ⇒ 119 ⇒ 78 ⇒ 49 ⇒ 87 ⇒ 48 ⇒ 123 ⇒ 71 ⇒ 83 ⇒ 94 ⇒ 57 ⇒ 91 ⇒ 106 ⇒ 77 ⇒ 65 ⇒ 59 ⇒ 92 ⇒ 115 ⇒ 82 ⇒ 118 ⇒ 107 ⇒ 75 ⇒ 104 ⇒ 89 ⇒ 56 ⇒ 44 ⇒ 40 ⇒ 121 ⇒ 35 ⇒ 93 ⇒ 98 ⇒ 84 ⇒ 61 ⇒ 100 ⇒ 97 ⇒ 46 ⇒ 101 ⇒ 99 ⇒ 86 ⇒ 95 ⇒ 109 ⇒ 88 ⇒ 47 ⇒ 52 ⇒ 72 ⇒ 55 ⇒ 110 ⇒ 126 ⇒ 64 ⇒ 81 ⇒ 54 ⇒ 90 ⇒ 124 ⇒ 34 ⇒ 122 ⇒ 63 ⇒ 43 ⇒ 36 ⇒ 38 ⇒ 113 ⇒ 108 ⇒ 39 ⇒ 116 ⇒ 69 ⇒ 112 ⇒ 68 ⇒ 33 ...
  • 37 ⇒ 103 ⇒ 117 ⇒ 111 ⇒ 120 ⇒ 58 ⇒ 37 ...
  • 41 ⇒ 102 ⇒ 96 ⇒ 60 ⇒ 51 ⇒ 41 ...
  • 42 ⇒ 114 ⇒ 125 ⇒ 105 ⇒ 42 ...
  • 50 ⇒ 80 ⇒ 66 ⇒ 62 ⇒ 76 ⇒ 79 ⇒ 67 ⇒ 85 ⇒ 73 ⇒ 50 ...
  • 70 ⇒ 74 ⇒ 70 ...

These cycles can be used to create loops that do different things each time and that eventually become repetitive. Lou Scheffer used this idea to create a Malbolge program (included in his cryptanalysis linked below) that repeats anything the user inputs.

Variants

Malbolge is not Turing-complete, due to its memory limits. However, it otherwise has sequential execution, repetition, and conditional-execution. Several attempts have been made to create Turing-complete versions of Malbolge:

  • Malbolge-T is a theoretical version of Malbolge that resets the input/output stream upon reaching the end, allowing for unbounded programs. Malbolge-T would be backward compatible with Malbolge.[9]
  • Malbolge Unshackled is a hopefully Turing-complete variation, allowing for programs of any length. However, due to command variations to allow for values above 257, valid Malbolge programs will not necessarily run correctly in Malbolge Unshackled.[10]

In the television series Elementary, during the episode "Leviathan" (season 1, episode 10), a clue written on a coffee order is described as having been written in Malbolge. It appears to be a small modification of the more verbose "Hello World" example shown above.[1][11]

See also

References

  1. ^ a b c d e f Temkin, Daniel (3 November 2014). "Interview with Ben Olmstead". esoteric.codes. Retrieved 2015-06-21.
  2. ^ "andrew cooke: malbolge "hello world"". Acooke.org. Retrieved 2012-11-06.
  3. ^ Programming in Malbolge. Lscheffer.com (2007-12-11). Retrieved on 2011-11-21.
  4. ^ "Malbolge - Progopedia - Encyclopedia of Programming Languages". progopedia.com. Retrieved 2015-06-21.
  5. ^ "Language Malbolge". 99 Bottles of Beer. Retrieved 2012-11-06.
  6. ^ a b IIZAWA, Hisashi. "Programming Method in Obfuscated Language Malbolge" (PDF). www.sakabe.i.is.nagoya-u.ac.jp (in Japanese). Graduate School of Information Science, Nagoya University Furo-cho, Chikusa-ku, Nagoya City, Aichi, 464–8603 Japan. Retrieved 2015-06-21.{{cite web}}: CS1 maint: location (link)
  7. ^ Green, Austin. "Malbolge". www2.latech.edu. Retrieved 2015-06-21.
  8. ^ Olmstead, Ben (1998). "Malbolge Specification". www.lscheffer.com. Retrieved 2015-06-21.
  9. ^ Scheffer, Lou. "Programming in Malbolge". www.lscheffer.com. Retrieved 2015-06-21.
  10. ^ Malbolge Unshackled – Esolang. Esolangs.org (2010-11-24). Retrieved on 2011-11-21.
  11. ^ "Leviathan". Elementary. Season 1. Episode 10. Manhattan. 2012-12-14. CBS.
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