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Getting started with BrainFuck

DPAmar
4,412 views

Sum numbers

As you probably already noticed, there is no "sum 2 variables" in BF. Variables actually don't exist either :)

The + command even does not "add" values : it simply increments current cell, so does the - command that decrements current cell.

In order to compute A+B, we have to add 1 to A, B times

Let's start

  • Memory: A, B
  • Cursor: on B
  • Input: any

Process

  • while B is not null
    • invariant: A cell + B cell = A+B
    • decrease B
    • increase A
  • loop
  • B cell = 0, A cell = A+B - 0 = A+B

Code

[    while B is not null
  -  decrease B
  <+ go to A and increase
  >  go back to B
]    loop

Minified version

[-<+>]

Final state

  • Memory: A+B, 0
  • Cursor: "0" cell
  • Input: unchanged
  • Output: unchanged
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