Function garner_crt 

pub fn garner_crt(residues: &[u32], moduli: &[u32]) -> BigUint

Garner’s algorithm: reconstruct the unsigned integer in [0, M) from its balanced-canonical residues. All intermediates stay within u64.

The mixed-radix step uses the underflow-safe form c[i] = ((c[i] + m_i - (c[j] % m_i)) % m_i) * inv % m_i.