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Comment by lifthrasiir | Hacker News Reader

My first attempt was to put Jon Ripley's Lost Kingdom [1] to the input and it obviously didn't work (or took too much time, I don't know). At the very least there is an asm.js version that does work out of the box [2].

[1] http://jonripley.com/i-fiction/games/LostKingdomBF.html

[2] https://github.com/rdebath/LostKingdom

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Looks like the default Lost Kingdom BF interpreter uses 8-bit cells, whereas the bf2wasm compiler uses 32-bit cells. This matters in Brainfuck; choosing the "wrong" one of the idioms [-] and [+] for zeroing a cell gets worse as cells get bigger. Maybe if you tweaked the bf2wasm compiler to use 8-bit cells?

Moreover, the Lost Kingdom interpreter will expand the memory arbitrarily as it encounters > instructions, whereas the bf2wasm interpreter has a fixed limit of 16384 4-byte cells according to its documentation.

Oh, you are right; I simply overlooked that part of the readme. In my opinion that should have been 8-bit cells mainly because AFAIK simulating 16-bit or 32-bit in 8-bit cells is reasonable [1] but doing the other way without slowing it down too much is highly dependent to the program.

[1] https://esolangs.org/wiki/Brainfuck_bitwidth_conversions

I didn't know about the idiom of using [+] for zeroing. Are the cells supposed to be signed ?

Signedness depends on your interpreter. In practice it hardly matters since there's no print function anyways, so if you want 2s complement you'll end up implementing it yourself anyways.

[+] should always overflow to 0 at some point, which is entirely doable for 8 bit, but less so for 32bit. as for choosing between [-] and [+] you'll just have to guesstimate if 0 or intmax is on average closer to your value.

> This matters in Brainfuck; choosing the "wrong" one of the idioms [-] and [+] for zeroing a cell gets worse as cells get bigger.

Translating these idioms to "*data = 0" was one of the first peephole optimizations I implemented when writing my own optimizing brainfuck interpreter.

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