ballistics-engine 0.25.0

High-performance ballistics trajectory engine with professional physics
Documentation 
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//! Minimal MD5 (RFC 1321), private to profile import.
//!
//! The .a7p format prefixes its payload with an MD5 hex digest; pulling in a
//! dependency for sixty lines of public-domain algorithm is not worth the
//! platform-matrix cost. File-integrity use only — MD5 is NOT a security hash.

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,
];

/// MD5 digest of `data`, as a lowercase hex string.
pub(crate) fn md5_hex(data: &[u8]) -> String {
    let (mut a0, mut b0, mut c0, mut d0) =
        (0x67452301u32, 0xefcdab89u32, 0x98badcfeu32, 0x10325476u32);

    let mut msg = data.to_vec();
    let bit_len = (data.len() as u64).wrapping_mul(8);
    msg.push(0x80);
    while msg.len() % 64 != 56 {
        msg.push(0);
    }
    msg.extend_from_slice(&bit_len.to_le_bytes());

    for chunk in msg.chunks_exact(64) {
        let mut m = [0u32; 16];
        for (i, w) in chunk.chunks_exact(4).enumerate() {
            m[i] = u32::from_le_bytes([w[0], w[1], w[2], w[3]]);
        }
        let (mut a, mut b, mut c, mut d) = (a0, b0, c0, d0);
        for i in 0..64 {
            let (f, g) = match i / 16 {
                0 => ((b & c) | (!b & d), i),
                1 => ((d & b) | (!d & c), (5 * i + 1) % 16),
                2 => (b ^ c ^ d, (3 * i + 5) % 16),
                _ => (c ^ (b | !d), (7 * i) % 16),
            };
            let tmp = d;
            d = c;
            c = b;
            b = b.wrapping_add(
                a.wrapping_add(f)
                    .wrapping_add(K[i])
                    .wrapping_add(m[g])
                    .rotate_left(S[i]),
            );
            a = tmp;
        }
        a0 = a0.wrapping_add(a);
        b0 = b0.wrapping_add(b);
        c0 = c0.wrapping_add(c);
        d0 = d0.wrapping_add(d);
    }

    let mut out = String::with_capacity(32);
    for word in [a0, b0, c0, d0] {
        for byte in word.to_le_bytes() {
            use std::fmt::Write as _;
            let _ = write!(out, "{byte:02x}");
        }
    }
    out
}

#[cfg(test)]
mod tests {
    use super::md5_hex;

    #[test]
    fn rfc1321_test_vectors() {
        // The seven official vectors from RFC 1321 appendix A.5.
        let cases: [(&str, &str); 7] = [
            ("", "d41d8cd98f00b204e9800998ecf8427e"),
            ("a", "0cc175b9c0f1b6a831c399e269772661"),
            ("abc", "900150983cd24fb0d6963f7d28e17f72"),
            ("message digest", "f96b697d7cb7938d525a2f31aaf161d0"),
            ("abcdefghijklmnopqrstuvwxyz", "c3fcd3d76192e4007dfb496cca67e13b"),
            (
                "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",
                "d174ab98d277d9f5a5611c2c9f419d9f",
            ),
            (
                "12345678901234567890123456789012345678901234567890123456789012345678901234567890",
                "57edf4a22be3c955ac49da2e2107b67a",
            ),
        ];
        for (input, expected) in cases {
            assert_eq!(md5_hex(input.as_bytes()), expected, "input {input:?}");
        }
    }

    #[test]
    fn multi_block_message() {
        // > 64 bytes forces multiple compression blocks; length padding straddles blocks.
        let input = vec![b'x'; 200];
        // Reference value verified independently via `python3 -c "import hashlib;
        // print(hashlib.md5(b'x'*200).hexdigest())"` (cross-checked with openssl/md5sum);
        // differs from the brief's draft constant, per Step 2a.
        assert_eq!(md5_hex(&input), "30a83621ce5422fbdfdd539777458c78");
    }
}