Floating point structure playground

ieee.py

from __future__ import division


def pretty_print_fp(x):
    print "---------------------------------------------"
    print "Floating point structure for %r" % x
    print "---------------------------------------------"
    import struct
    s = struct.pack("d", x)
    print "Hex pattern:", " ".join("%02x" % ord(i) for i in s[::-1])

    def get_bit(i):
        byte_nr, bit_nr = divmod(i, 8)
        return int(bool(
            ord(s[byte_nr]) & (1 << bit_nr)
            ))

    def get_bits(lsb, count):
        return sum(get_bit(i+lsb)*2**i for i in xrange(count))

    # https://en.wikipedia.org/wiki/Double_precision_floating-point_format

    print "Sign bit (1:negative):", get_bit(63)
    exponent = get_bits(52, 11)
    print "Exponent: %d (unshifted: %d)" % (exponent - 1023, exponent)
    mantissa = get_bits(0, 52)
    print "Mantissa:", hex(mantissa)
    mantissa_with_one = mantissa + 2**52
    print "Mantissa with implied one:", hex(mantissa_with_one)
    mantissa_with_one = mantissa + 2**52
    print "Shifted Mantissa with implied one:", mantissa_with_one / (2**52)

pretty_print_fp(1+2**-52)