Crate snafu_numbers 

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).

Conversion is implemented via the FromSnafu/TryFromSnafu and IntoSnafu traits.

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:

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 2×5^n-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’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

use snafu_numbers::IntoSnafu;
assert_eq!(1747_u32.into_snafu(), "1=-0-2");
assert_eq!(1257_u32.into_snafu(), "20012");
assert_eq!(3_u32.into_snafu(), "1=");

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

Example conversion from SNAFU to decimal

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);

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

Enums

ConversionError

Traits

FromSnafu

Provides conversion from SNAFU numbers.

IntoSnafu

Provides conversion into SNAFU numbers.

TryFromSnafu

Provides fallible conversion from SNAFU numbers.