import struct

# Returns the exponent and mantissa
def em(x):
    u = struct.unpack('>Q', struct.pack('>d', x))[0]

    e = ((u >> 52) & 0x7ff)
    m = u & 0xfffffffffffff

    # 1023 is an exponent bias
    return e - 1023, m


x = 255.123
e, m = em(x)

if e >= 53:
    print('large')
    fbits = 0
    ipart = m
    fpart = 0
elif e >= 0:
    print('integral and fraction')
    fbits = 52 - e
    ipart = m >> fbits
    fpart = m & ((1 << fbits) - 1)
else:
    print('only fraction')
    fbits = 52 - e
    ipart = 0
    fpart = m

print('int:', 2**e + ipart)
print('val:', 2**e + ipart + fpart / (1 << fbits))