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:
rust
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:
rust
use snafu_numbers::IntoSnafu;
assert_eq!(1747_u32.into_snafu(), "1=-0-2");
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:
| SNAFU digit | Name | Decimal / ℤ |
|-------------|--------------|-------------|
| 2 | two | 2 |
| 1 | one | 1 |
| 0 | zero | 0 |
| - | minus | -1 |
| = | double-minus | -2 |
As a result, the individual values in each position n is 2×5n-1, so
| Position | Base | = | - | 0 | 1 | 2 |
|----------|------------------------|---------|---------|-----|--------|--------|
| 0 | 50 = 1 | -2 | 1 | 0 | 1 | 2 |
| 1 | 51 = 5 | -10 | -5 | 0 | 5 | 10 |
| 2 | 52 = 25 | -50 | -25 | 0 | 25 | 50 |
| 3 | 53 = 125 | -250 | -125 | 0 | 125 | 250 |
| 4 | 54 = 625 | -1250 | -625 | 0 | 625 | 1250 |
| 5 | 55 = 3125 | -6250 | -3125 | 0 | 3125 | 6250 |
etc.
To quote the rules:
Say you have the SNAFU number
2=-01. That's2in the 625s place,=(double-minus) in the 125s place,-(minus) in the 25s place,0in the 5s place, and 1 in the1s 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!"
| Decimal | SNAFU |
|-------------|-----------------|
| 1 | 1 |
| 2 | 2 |
| 3 | 1= |
| 4 | 1- |
| 5 | 10 |
| 6 | 11 |
| 7 | 12 |
| 8 | 2= |
| 9 | 2- |
| 10 | 20 |
| 15 | 1=0 |
| 20 | 1-0 |
| 2022 | 1=11-2 |
| 12345 | 1-0---0 |
| 314159265 | 1121-1110-1=0 |
| SNAFU | Decimal |
|----------|---------|
| 1=-0-2 | 1747 |
| 12111 | 906 |
| 2=0= | 198 |
| 21 | 11 |
| 2=01 | 201 |
| 111 | 31 |
| 20012 | 1257 |
| 112 | 32 |
| 1=-1= | 353 |
| 1-12 | 107 |
| 12 | 7 |
| 1= | 3 |
| 122 | 37 |