$ ctf42

Emoji_Stack

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Author: CACI

Flag format: pctf{...}

Welcome to Emoji Stack, the brand new stack based emoji language! Instead of other stack based turing machines that use difficult to read and challenging characters like + - and [], Emoji Stack uses our proprietary patent pending emoji system.

The details of our implentation is below:

👉: Move the stack pointer one cell to the right
👈: Move the stack pointer one cell to the lef
👍: Increment the current cell by one, bounded by 255
👎: Decrement the current cell by one, bounded by 0
💬: Print the ASCII value of the current cell
🔁##: Repeat the previous instruction 0x## times

The Emoji Stack is 256 cells long, with each cell supporting a value between 0 - 255.

As an example, the program "👍🔁47💬👉👍🔁68💬👉👍🔁20💬" Would output "Hi!" with the following execution flow:

[0, 0, 0, 0] 👍🔁47

[0x48, 0, 0, 0] 💬👉: H

[0x48, 0, 0, 0] 👍🔁68

[0x48, 0x69, 0, 0] 💬👉: i

[0x48, 0x69, 0, 0] 👍🔁20

[0x48, 0x69, 0x21, 0] 💬: !

Author: CACI

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