malt 0.1.1

Merkle Append-Only Log Tree (RFC 9162 §2.1)
Documentation 
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//! Shared test utilities for MALT integration tests.

use malt::TreeHasher;

const FNV_OFFSET: u64 = 0xcbf29ce484222325;
const FNV_PRIME: u64 = 0x00000100000001B3;

fn fnv1a(data: &[u8]) -> [u8; 8] {
    let mut hash = FNV_OFFSET;
    for &byte in data {
        hash ^= byte as u64;
        hash = hash.wrapping_mul(FNV_PRIME);
    }
    hash.to_be_bytes()
}

/// A deterministic, domain-separating test hasher using FNV-1a (64-bit).
///
/// NOT cryptographically secure — only used for invariant testing.
pub struct SimpleHasher;

impl TreeHasher for SimpleHasher {
    type Digest = [u8; 8];

    fn leaf(&self, data: &[u8]) -> [u8; 8] {
        let mut buf = Vec::with_capacity(1 + data.len());
        buf.push(0x00);
        buf.extend_from_slice(data);
        fnv1a(&buf)
    }

    fn node(&self, left: &[u8; 8], right: &[u8; 8]) -> [u8; 8] {
        let mut buf = Vec::with_capacity(1 + 8 + 8);
        buf.push(0x01);
        buf.extend_from_slice(left);
        buf.extend_from_slice(right);
        fnv1a(&buf)
    }

    fn empty(&self) -> [u8; 8] {
        fnv1a(&[])
    }
}

/// Build a log with n leaves using sequential leaf data.
pub fn build_log(n: u64) -> malt::Log<SimpleHasher> {
    let mut log = malt::Log::new(SimpleHasher);
    for i in 0..n {
        log.append(format!("leaf-{i}").as_bytes());
    }
    log
}