بهینه سازی رمزگشایی u128 از base62

const BASE62_N: usize = 62;

pub fn base62_to_u128_naive(base62_str: &str) -> Option<u128> {
    let base62_str: [u8; 22] = base62_str.as_bytes().try_into().ok()?;
    let mut n: u128 = 0;
    for digit in &base62_str {
        let number = match digit {
            d if (b'0'..=b'9').contains(d) => d - 48,
            d if (b'A'..=b'Z').contains(d) => d - 55,
            d if (b'a'..=b'z').contains(d) => d - 61,
            _ => return None,
        };
        n = n
            .checked_mul(BASE62_N as u128)
            .and_then(|n| n.checked_add(number as u128))?;
    }
    Some(n)
}

fn base62_to_u128_naive(base62_str: &str) -> Option<u128>

let base62_str: [u8; 22] = base62_str.as_bytes().try_into().ok()?;

for digit in &base62_str

let number = match digit

n = n.checked_mul(BASE62_N as u128).and_then(|n| n.checked_add(number as u128))?;

Some(n)

bench_base62_to_u128_naive 1000000: 0.121s 125.75Mib/s, 8240895.48/s

const BASE62_MAP: [u8; 123] = [
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255,
    255, 255, 255, 255, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
    29, 30, 31, 32, 33, 34, 35, 255, 255, 255, 255, 255, 255, 36, 37, 38, 39, 40, 41, 42, 43, 44,
    45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
];

for digit in &base62_str[..21] {
        // ...
        n = n * BASE62_N as u128 + number as u128;
}

3322222222221111111111 -> 33 2222222222 1111111111
                          n3         n2         n1
n = n3 * 62^20 + n2 * 62^10 + n1

const BASE62_N: usize = 62;
const BASE62_POW_10: u128 = (BASE62_N as u128).pow(10);
const BASE62_POW_20: u128 = (BASE62_N as u128).pow(20);
const BASE62_MAP: [u8; 123] = [
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255,
    255, 255, 255, 255, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
    29, 30, 31, 32, 33, 34, 35, 255, 255, 255, 255, 255, 255, 36, 37, 38, 39, 40, 41, 42, 43, 44,
    45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
];

pub fn base62_to_u128(base62_str: &str) -> Option<u128> {
    let base62_str: [u8; 22] = base62_str.as_bytes().try_into().ok()?;
    let mut n_section: u64 = 0;
    for digit in &base62_str[12..22] {
        let number = *BASE62_MAP.get(*digit as usize).filter(|it| **it <= 61)?;
        n_section = n_section * BASE62_N as u64 + number as u64;
    }
    let mut n = n_section as u128;
    n_section = 0;
    for digit in &base62_str[2..12] {
        let number = *BASE62_MAP.get(*digit as usize).filter(|it| **it <= 61)?;
        n_section = n_section * BASE62_N as u64 + number as u64;
    }
    n += n_section as u128 * BASE62_POW_10;
    n_section = 0;
    for digit in &base62_str[0..2] {
        let number = *BASE62_MAP.get(*digit as usize).filter(|it| **it <= 61)?;
        n_section = n_section * BASE62_N as u64 + number as u64;
    }
    n.checked_add((n_section as u128).checked_mul(BASE62_POW_20)?)
}

for digit in &base62_str[12..22]
// ...
for digit in &base62_str[2..12]
// ...
for digit in &base62_str[0..2]
// ..

let number = *BASE62_MAP.get(*digit as usize).filter(|it| **it <= 61)?;

n.checked_add((n_section as u128).checked_mul(BASE62_POW_20)?)

bench_base62_to_u128 10000000: 0.182s 836.24Mib/s, 54803747.40/s