py_ecc/bls/utils.py
def compress_G1(pt: G1Uncompressed) -> G1Compressed:
    """
    A compressed point is a 384-bit integer with the bit order (c_flag, b_flag, a_flag, x),
    where the c_flag bit is always set to 1,
    the b_flag bit indicates infinity when set to 1,
    the a_flag bit helps determine the y-coordinate when decompressing,
    and the 381-bit integer x is the x-coordinate of the point.
    """
    if is_inf(pt):
        # Set c_flag = 1 and b_flag = 1. leave a_flag = x = 0
        return G1Compressed(POW_2_383 + POW_2_382)
    else:
        x, y = normalize(pt)
        # Record y's leftmost bit to the a_flag
        a_flag = (y.n * 2) // q
        # Set c_flag = 1 and b_flag = 0
        return G1Compressed(x.n + a_flag * POW_2_381 + POW_2_383)
def compress_G1(pt: G1Uncompressed) -> G1Compressed:
    """
    A compressed point is a 384-bit integer with the bit order (c_flag, b_flag, a_flag, x),
    where the c_flag bit is always set to 1,
    the b_flag bit indicates infinity when set to 1,
    the a_flag bit helps determine the y-coordinate when decompressing,
    and the 381-bit integer x is the x-coordinate of the point.
    """
    if is_inf(pt):
        # Set c_flag = 1 and b_flag = 1. leave a_flag = x = 0
        return G1Compressed(POW_2_383 + POW_2_382)
    else:
        x, y = normalize(pt)
        # Record y's leftmost bit to the a_flag
        a_flag = (y.n * 2) // q
        # Set c_flag = 1 and b_flag = 0
        return G1Compressed(x.n + a_flag * POW_2_381 + POW_2_383)
A compressed point is a 384-bit integer with the bit order (c_flag, b_flag, a_flag, x),
    where the c_flag bit is always set to 1,
    the b_flag bit indicates infinity when set to 1,
    the a_flag bit helps determine the y-coordinate when decompressing,
    and the 381-bit integer x is the x-coordinate of the point.