David James David James - 4 months ago 26
Brainfuck Question

Brainfuck Interpreter

Will somebody please describe this brainfuck interpreter for me??

#include <stdlib.h>
char m[9999], *n[99], *r = m, *p = m + 5000, **s = n, d, c;
main()
{
for (read(0, r, 4000); c = *r; r++)
c - ']' || (d > 1 ||
(r = *p ? *s : (--s, r)), !d || d--), c - '[' || d++ ||
(*++s = r), d || (*p += c == '+', *p -= c == '-', p += c == '>',
p -= c == '<', c - '.' || write(2, p, 1), c - ',' || read(2, p, 1));
}

MSN MSN
Answer

The inner loop uses a short circuiting boolean expression (and the comma operator instead of a semicolon) to evaluate each brainfuck token.

Each instance of <expr a> || <expr b> can be translated into if (!<expr a>) { <expr b> }

Each use of the comma operator outside of (r = *p ? *s : (--s, r)) can be replaced with a semicolon.

The list of p <op>= <conditional> and *p+= <conditional> can be replaced with if (<conditional>) p <op>= 1 and if (<conditional>) *p <op>= 1. And that whole parenthesized collection can be transformed into if (!d) { ... }.

Once you've done all that you end up with a pretty simple brainfuck interpreter. Just remember, the comma operator as an expression evaluates left to right.

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