Function logos_band_exact 

pub fn logos_band_exact(a: impl Into<LogosInt>, b: impl Into<LogosInt>) -> i64

a & b on exact integers, as every tier computes it: two machine words AND bit by bit, and a big integer that is not negative, beside a low mask 2^k - 1, leaves its low k bits. Any other big operand is refused in crate::failure::BITAND_OPERANDS’s words.