Wikipedia

Malbolge

This article is about the programming language. For the eighth circle of hell in Dante's Inferno, see Malebolge.

Malbolge (/mælˈboʊldʒ/) 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. It was specifically designed to be almost impossible to use, via a counter-intuitive 'crazy operation', base-three arithmetic, and self-altering code.[2] It builds on the difficulty of earlier challenging esoteric languages (such as Brainfuck and Befunge), but exaggerates this aspect to an extreme degree, playing on the entangled histories of computer science and encryption. Despite this design, it is possible to write useful Malbolge programs.

Malbolge
A cat program in Malbolge
ParadigmEsoteric, imperative, scalar, value-level
Designed byBen Olmstead[1]
DeveloperBen Olmstead[1]
First appeared1998
Typing disciplineUntyped
Filename extensions.mal, .mb
Influenced by
Brainfuck, INTERCAL (Tri-INTERCAL), Befunge
Influenced
Dis, Malbolge Unshackled

Programming in Malbolge

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Malbolge was very difficult to understand when it arrived, taking two years for the first Malbolge program to appear. The author himself has never written a Malbolge program.[2] 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.[3]

Later, Lou Scheffer posted a cryptanalysis of Malbolge and provided a program to copy its input to its output.[4] 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.[5]

Olmstead believed Malbolge to be a linear bounded automaton. There's 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.[6] Hisashi Iizawa et al. also proposed a guide for programming in Malbolge for the purpose of obfuscation for software protection.[7]

In 2020, Kamila Szewczyk published a Lisp interpreter in Malbolge Unshackled.[8]

Example programs

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Hello, World!

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This program displays "Hello, World."[9] 

(=<`#9]~6ZY327Uv4-QsqpMn&+Ij"'E%e{Ab~w=_:]Kw%o44Uqp0/Q?xNvL:`H%c#DD2^WV>gY;dts76qKJImZkj

cat program

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This program reads a string from a user and prints that string, similar to the Unix command-line utility cat.[10]

(=BA#9"=<;:3y7x54-21q/p-,+*)"!h%B0/.
~P<
<:(8&
66#"!~}|{zyxwvu
gJ%

Design

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

The standard interpreter and the official specification do not match perfectly.[11] 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".[2]

Registers

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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.[12] 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

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

Memory

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The virtual machine has 59,049 (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.[2]

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).

Note that the official specification does not cover the edge case of 1-instruction programs, where trying to fill the second memory position using the crazy operation, as indicated before, will result in [m - 2] pointing outside the program's memory region. The reference implementation does not explicitly consider this case either and incurs in undefined behavior.[13]

In 2007, Ørjan Johansen created Malbolge Unshackled, a version of Malbolge which does not have the arbitrary memory limit. The hope was to create a Turing-complete language while keeping as much in the spirit of Malbolge as possible. No other rules are changed, and all Malbolge programs that do not reach the memory limit are still completely functional.[14]

Instructions

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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] Copies the value at [d] to c. Note that c will still be incremented after execution of this instruction, so the next instruction to be executed will be the one at [d] + 1 (modulo 59049).
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 to the right (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, it gets encrypted (see below) so that it will not do the same thing next time, unless a jump just happened. Right after a jump, Malbolge will encrypt the 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

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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 1120020211.

Crazy operation[2][7]
crz Input 1
0 1 2
Input 2 0 1 0 0
1 1 0 2
2 2 2 1

Encipherment

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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 enciphered 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 permutation. 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

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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:

  • Malbolge20 is a version of Malbolge with an expanded word-size of 20 trits, allowing one to write a program with a size of up to ~3.4 gigabytes.[15]
  • 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.[4]
  • 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.[16]

See also

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References

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  1. ^ a b "Malbolge - Esolang". Archived from the original on 2022-08-27. Retrieved 2022-08-27.
  2. ^ a b c d e Temkin, Daniel (2014-11-03). "Interview with Ben Olmstead". esoteric.codes. Archived from the original on 2023-03-20. Retrieved 2021-01-07.
  3. ^ Cooke, Andrew. "malbolge: hello world". Archived from the original on 2019-12-06. Retrieved 2021-01-08.
  4. ^ a b Scheffer, Lou (2015-04-17). "Introduction to Malbolge". Archived from the original on 2023-06-11. Retrieved 2017-06-09.
  5. ^ Mykhailova, Mariya (2012-05-11). "Malbolge - Programming language". Progopedia. Archived from the original on 2023-06-09. Retrieved 2017-06-09.
  6. ^ "Language Malbolge". 99 Bottles of Beer. 2005-12-29. Archived from the original on 2020-05-14. Retrieved 2020-11-19.
  7. ^ a b IIZAWA, Hisashi. "Programming Method in Obfuscated Language Malbolge" (PDF) (in Japanese). Nagoya University. Archived (PDF) from the original on 2017-06-23. Retrieved 2017-06-09.
  8. ^ Laughlin, Gregory (2022-03-26). "Malbolge (a second look)". oklo. Retrieved 2023-10-24.
  9. ^ Palaiologos (2021-03-04), kspalaiologos/hello.mb, archived from the original on 2021-08-05, retrieved 2021-03-23
  10. ^ Lutter, Matthias. "Malbolge cat". lutter.cc. Archived from the original on 2022-08-28. Retrieved 2022-08-28.
  11. ^ Green, Austin (2000-12-01). "Malbolge". Louisiana Tech University. Archived from the original on 2017-07-09. Retrieved 2017-06-09.
  12. ^ Olmstead, Ben (1998). "Malbolge Specification". www.lscheffer.com. Archived from the original on 2017-06-11. Retrieved 2017-06-09.
  13. ^ Olmstead, Ben (1998). "Malbolge reference interpreter". www.lscheffer.com. Archived from the original on 2024-08-08. Retrieved 2024-09-27.
  14. ^ Johansen, Ørjan (2013-10-25). "An interpreter for the Malbolge Unshackled dialect" (Haskell). oerjan.nvg.org. Retrieved 2017-06-09.
  15. ^ "Malbolge20 - Esolang". esolangs.org. Archived from the original on 2022-12-12. Retrieved 2022-12-12.
  16. ^ "Malbolge Unshackled". esolangs.org. 2017-04-14. Retrieved 2017-06-09.
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