abrupt 0.1.0-beta.1

A Rust library for cryptographic and mathematical operations
Documentation 
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const S: [u32; 64] = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9,
    14, 20, 5, 9, 14, 20, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 6, 10, 15,
    21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21,
];

const K: [u32; 64] = [
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee, 0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be, 0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05, 0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1, 0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391,
];

fn left_rotate(x: u32, c: u32) -> u32 {
    (x << c) | (x >> (32 - c))
}

fn padding(input: &[u8]) -> Vec<u8> {
    let mut padded = input.to_vec();
    padded.push(0x80);
    while (padded.len() % 64) != 56 {
        padded.push(0);
    }
    let bit_len = (input.len() as u64) * 8;
    padded.extend_from_slice(&bit_len.to_le_bytes());
    padded
}

fn process_block(block: &[u8], hash: &mut [u32; 4]) {
    let mut a = hash[0];
    let mut b = hash[1];
    let mut c = hash[2];
    let mut d = hash[3];

    let mut w = [0u32; 16];
    for i in 0..16 {
        w[i] = u32::from_le_bytes([
            block[4 * i],
            block[4 * i + 1],
            block[4 * i + 2],
            block[4 * i + 3],
        ]);
    }

    for i in 0..64 {
        let (f, g) = match i {
            0..=15 => ((b & c) | ((!b) & d), i),
            16..=31 => ((d & b) | ((!d) & c), (5 * i + 1) % 16),
            32..=47 => (b ^ c ^ d, (3 * i + 5) % 16),
            48..=63 => (c ^ (b | (!d)), (7 * i) % 16),
            _ => unreachable!(),
        };

        let temp = d;
        d = c;
        c = b;
        b = b.wrapping_add(left_rotate(
            a.wrapping_add(f).wrapping_add(K[i]).wrapping_add(w[g]),
            S[i],
        ));
        a = temp;
    }

    hash[0] = hash[0].wrapping_add(a);
    hash[1] = hash[1].wrapping_add(b);
    hash[2] = hash[2].wrapping_add(c);
    hash[3] = hash[3].wrapping_add(d);
}

pub fn md5(input: &[u8]) -> [u8; 16] {
    let mut hash = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476];
    let padded = padding(input);

    for chunk in padded.chunks(64) {
        process_block(chunk, &mut hash);
    }

    let mut result = [0u8; 16];
    for (i, &h) in hash.iter().enumerate() {
        result[4 * i..4 * i + 4].copy_from_slice(&h.to_le_bytes());
    }
    result
}