Python int12

python_int12.py

def pack(arr):
    """Pack integers < 2**12 into 12 bit integers, encoded as bytes"""
    out = []
    for i in range(0, len(arr), 2):
        e1, e2 = arr[i:i+2]
        assert 0 <= e1 < 2**12
        assert 0 <= e2 < 2**12
        e1 = (e1 << 4) | (e2 >> 8)
        e2 &= 2**8-1
        assert e1 <= 2**16-1
        out.extend([e1 >> 8, e1 & 2**8-1, e2])
    return out


def unpack(arr):
    """Unpack 12 bit integers, encoded as bytes."""
    out = []
    for i in range(0, len(arr), 3):
        e1, e2, e3 = arr[i:i+3]
        assert 0 <= e1 < 2**8
        assert 0 <= e2 < 2**8
        assert 0 <= e2 < 2**8
        n1 = e1 << 4 | e2 >> 4
        n2 = (e2 & 0xf) << 8 | e3
        out.extend([n1, n2])
    return out