Special Numeral-Analogue Fuel Units

A Rust crate and utility to deal with conversions of SNAFU values from Advent of Code 2022, Day 25 (here). The file AOC-22-25.md contains the full puzzle in case the website is unavailable.

Example conversions from SNAFU:

use snafu_numbers::FromSnafu;
assert_eq!(u32::from_snafu("1=-0-2"), 1747);
assert_eq!(u32::from_snafu("20012"), 1257);
assert_eq!(u32::from_snafu("1="), 3);

... and into SNAFU:

use snafu_numbers::IntoSnafu;
assert_eq!(1747_u32.into_snafu(), "1=-0-2");

SNAFU numbers

SNAFU numbers are a power-of-5 centric base-10 system written right to left. The zero-th (i.e., right-most) place represents a multiple of 5⁰ = 0, the first represents a multiple 5¹ = 5, the second place 5² = 25, the third place 5³ = 625, etc.

Five different digits are used. Here is a list alongside their decimal integer representation:

As a result, the individual values in each position n is 2×5^n-1, so

etc.

To quote the rules:

Say you have the SNAFU number 2=-01. That's 2 in the 625s place, = (double-minus) in the 125s place, - (minus) in the 25s place, 0 in the 5s place, and 1 in the 1s place. (2 times 625) plus (-2 times 125) plus (-1 times 25) plus (0 times 5) plus (1 times 1). That's 1250 plus -250 plus -25 plus 0 plus 1. 976!"

Example conversion from decimal to SNAFU

Example conversion from SNAFU to decimal