const-murmur3 0.3.0

A const fn implementation of the murmur3 hashing algorithm
Documentation 
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#![no_std]

#[cfg(test)]
mod tests {
    use super::murmur3_32;
    #[test]
    fn standard_murmur3_32() {
        assert_eq!(murmur3_32(&[], 0), 0);
        assert_eq!(murmur3_32(&[], 1), 0x514E28B7);
        assert_eq!(murmur3_32(&[], 0xffffffff), 0x81F16F39);
        assert_eq!(murmur3_32(&[0, 0, 0, 0], 0), 0x2362F9DE);
        assert_eq!(murmur3_32(&[0x74, 0x61, 0x72, 0x69], 0), 0x78ab8db9);
        assert_eq!(
            murmur3_32(&[0x21, 0x43, 0x65, 0x87], 0x5082EDEE),
            0x2362F9DE
        );
        assert_eq!(murmur3_32(&[0x21, 0x43, 0x65], 0), 0x7E4A8634);
        assert_eq!(murmur3_32(&[0x21, 0x43], 0), 0xA0F7B07A);
        assert_eq!(murmur3_32(&[0x21], 0), 0x72661CF4);
    }
}

/// A const fn implementation of the murmur32_32 algorithm
pub const fn murmur3_32(data: &[u8], seed: u32) -> u32 {
    let slice_size: usize = data.len();

    let c1: u32 = 0xcc9e2d51;
    let c2: u32 = 0x1b873593;
    let r2 = 13;
    let m = 5;
    let n: u32 = 0xe6546b64;

    let mut hash = seed;

    let mut i = 0;
    let iterator = slice_size / 4;
    while i < iterator {
        let data = [
            data[i * 4],
            data[i * 4 + 1],
            data[i * 4 + 2],
            data[i * 4 + 3],
        ];
        let mut k = u32::from_le_bytes(data);
        k = k.wrapping_mul(c1);
        k = k.rotate_left(15);
        k = k.wrapping_mul(c2);

        hash = hash ^ k;
        hash = hash.rotate_left(r2);
        hash = hash.wrapping_mul(m).wrapping_add(n);

        i += 1;
    }
    match slice_size % 4 {
        0 => (),
        1 => {
            let data = [data[i * 4], 0, 0, 0];
            let k = mix_bytes_32(data);
            hash = hash ^ k;
        }
        2 => {
            let data = [data[i * 4], data[i * 4 + 1], 0, 0];
            let k = mix_bytes_32(data);
            hash = hash ^ k;
        }
        3 => {
            let data = [data[i * 4], data[i * 4 + 1], data[i * 4 + 2], 0];
            let k = mix_bytes_32(data);
            hash = hash ^ k;
        }
        _ => unsafe { core::hint::unreachable_unchecked() },
    }

    hash = hash ^ slice_size as u32;
    hash = hash ^ (hash.wrapping_shr(16));
    hash = hash.wrapping_mul(0x85ebca6b);
    hash = hash ^ (hash.wrapping_shr(13));
    hash = hash.wrapping_mul(0xc2b2ae35);
    hash = hash ^ (hash.wrapping_shr(16));

    hash
}

const fn mix_bytes_32(data: [u8; 4]) -> u32 {
    let r1 = 15;
    let c1: u32 = 0xcc9e2d51;
    let c2: u32 = 0x1b873593;
    let mut k = u32::from_le_bytes(data);
    k = k.wrapping_mul(c1);
    k = k.rotate_left(r1);
    k = k.wrapping_mul(c2);
    return k;
}