ring/arithmetic/
constant.rs

1use crate::limb::LeakyLimb;
2use core::mem::size_of;
3
4const fn parse_digit(d: u8) -> u8 {
5    match d.to_ascii_lowercase() {
6        b'0'..=b'9' => d - b'0',
7        b'a'..=b'f' => d - b'a' + 10,
8        _ => panic!(),
9    }
10}
11
12// TODO: this would be nicer as a trait, but currently traits don't support const functions
13pub const fn limbs_from_hex<const LIMBS: usize>(hex: &str) -> [LeakyLimb; LIMBS] {
14    let hex = hex.as_bytes();
15    let mut limbs = [0; LIMBS];
16    let limb_nibbles = size_of::<LeakyLimb>() * 2;
17    let mut i = 0;
18
19    while i < hex.len() {
20        let char = hex[hex.len() - 1 - i];
21        let val = parse_digit(char);
22        limbs[i / limb_nibbles] |= (val as LeakyLimb) << ((i % limb_nibbles) * 4);
23        i += 1;
24    }
25
26    limbs
27}