Function bloom_bit_pos

nodedb-columnar/src/predicate.rs:386–395

Compute the i-th hash slot for a string value in an `m`-bit filter. Uses FNV-1a seeded with different constants for each hash function to produce independent bit positions. `m` must be a power of two so the bitmask `m - 1` is exact.

(value: &str, hash_idx: u32, m: u32)

/// produce independent bit positions. `m` must be a power of two so the
/// bitmask `m - 1` is exact.
fn bloom_bit_pos(value: &str, hash_idx: u32, m: u32) -> usize {
    // Mix the hash index into the seed to produce distinct hash functions.
    let mut hash = FNV_OFFSET ^ (hash_idx as u64).wrapping_mul(FNV_PRIME);
    for byte in value.bytes() {
        hash ^= byte as u64;
        hash = hash.wrapping_mul(FNV_PRIME);
    }
    // Map to [0, m).  m is always a power of two so (m - 1) is a valid mask.
    (hash as usize) & ((m as usize) - 1)
}

/// Insert a string value into a `BloomFilter`.
pub fn bloom_insert(bloom: &mut BloomFilter, value: &str) {