original.name="While_Valid_18"
======
>>> main.whiley
type nat is (int x) where x >= 0

function match(byte[] data, nat offset, nat end) -> int:
    nat pos = end
    int len = 0
    while offset < pos && pos < |data| && data[offset] == data[pos] 
        where (pos >= 0) && (offset >= 0):
        //
        offset = offset + 1
        pos = pos + 1
        len = len + 1
    //
    return len

public export method test() :
    byte[] xs = [
        0b0000_0000,
        0b0000_0101,
        0b0000_0000,
        0b0000_0110,
        0b0000_0000,
        0b0000_0101
    ]
    int x = match(xs, 0, |xs| - 2)
    assume x == 2

---