_struct.py 文件源码

def float_unpack(Q, size, le):
    """Convert a 32-bit or 64-bit integer created
    by float_pack into a Python float."""

    if size == 8:
        MIN_EXP = -1021  # = sys.float_info.min_exp
        MAX_EXP = 1024   # = sys.float_info.max_exp
        MANT_DIG = 53    # = sys.float_info.mant_dig
        BITS = 64
    elif size == 4:
        MIN_EXP = -125   # C's FLT_MIN_EXP
        MAX_EXP = 128    # FLT_MAX_EXP
        MANT_DIG = 24    # FLT_MANT_DIG
        BITS = 32
    else:
        raise ValueError("invalid size value")

    if Q >> BITS:
         raise ValueError("input out of range")

    # extract pieces
    sign = Q >> BITS - 1
    exp = (Q & ((1 << BITS - 1) - (1 << MANT_DIG - 1))) >> MANT_DIG - 1
    mant = Q & ((1 << MANT_DIG - 1) - 1)

    if exp == MAX_EXP - MIN_EXP + 2:
        # nan or infinity
        result = float('nan') if mant else float('inf')
    elif exp == 0:
        # subnormal or zero
        result = math.ldexp(float(mant), MIN_EXP - MANT_DIG)
    else:
        # normal
        mant += 1 << MANT_DIG - 1
        result = math.ldexp(float(mant), exp + MIN_EXP - MANT_DIG - 1)
    return -result if sign else result