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BrainFuck part 7 - Quine (+ some non-BF quine theory)

DPAmar
2,133 views

BF quine

Let's start our BF quine. What to we need ?

  • A data block
  • A way to replicate the data block as data
  • A way to print the data block, as contents

Given a data block as an array of chars, it's not really complex to do the 3rd part : for each char in memory, print it.

The second part is a bit more complex. Let's have in memory value 44 for example, how can we write code to generate 44?

There is no need to find a complex solution to this (with multiplications 4x11 or similar). Let's just have 44 times '+', then '>' to move to the next cell.

Let's start

  • Memory: empty
  • Cursor: first cell
  • Input: any

Process

  • Leave 4 empty cells
  • Data definition - to be competed - a set of '+' and '>' that will fill memory
  • Generate and print '>' 4 times (the first "Leave 4 empty cells" command)
  • Then go to data array first cell
  • Generate just before values 43(+) and 62(>)
  • For each cell
    • Move 3 cells to the left, and on every +1/-1 step print the 43(+)
    • Print the 62(>)
    • Move the 43 and 62 one cell on the right
  • Loop
  • Go to array first cell
  • For each cell
    • print char
  • Loop

Code

>>>>                               leave 4 empty cells
$$$data definition$$$              to be completed
++++++++[->++++++++<]>--....[-]    print (62) 4 times
<<[<]<                             go 2 cells before array
<++++++++[->+++++>++++++++<<]      generate 40 and 64
>+++>-->                           then 43 and 62 and got to first data cell
[                                  for each cell
  [-<<<+>.>>]                      move value 3 cells on the left and print 43 each time
  <.                               print 62
  [->+<]<[->+<]                    moves 43 and 62 on the right
>>>]                               loop
<<<<[<]>                           Go to first array cell
[.>]                               For each cell print char

Minified version

>>>>$$$data definition$$$++++++++[->++++++++<]>--....[-]<<[<]<<++++++++[->+++++>++++++++<<]>+++>-->[[-<<<+>.>>]<.[->+<]<[->+<]>>>]<<<<[<]>[.>]

Final state

  • Memory: some garbage data
  • Cursor: after the data array
  • Input: unchanged
  • Output: unchanged
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