Question

我有Python浮点值，我需要将其转换为Microsoft Basic Float（MBF）格式。幸运的是，从互联网上得到了一些相反的代码。

def fmsbin2ieee(self,bytes):
    """Convert an array of 4 bytes containing Microsoft Binary floating point
    number to IEEE floating point format (which is used by Python)"""
    as_int = struct.unpack("i", bytes)
    if not as_int:
        return 0.0
    man = long(struct.unpack('H', bytes[2:])[0])
    exp = (man & 0xff00) - 0x0200
    if (exp & 0x8000 != man & 0x8000):
        return 1.0
        #raise ValueError('exponent overflow')
    man = man & 0x7f | (man << 8) & 0x8000
    man |= exp >> 1
    bytes2 = bytes[:2]
    bytes2 += chr(man & 255)
    bytes2 += chr((man >> 8) & 255)
    return struct.unpack("f", bytes2)[0]

现在我需要扭转这个过程，但还没有成功。请帮忙。

Answer 1

如果您要在Windows下运行时执行这些转换，则可以更快地下载并安装mbf2ieee.exe并调用生成的CVS提供的Mbf2ieee.dll功能（例如，通过[ctypes的] [2]）。

如果你热衷于使用纯Python，我认为（但我无法测试，手头没有MBF编号），以下内容可能会起作用（我只是从C code here将其移植到Python ）：

def mbf2ieee(mbf_4bytestring):
  msbin = struct.unpack('4B', mbf_4bytestring)
  if msbin[3] == 0: return 0.0

  ieee = [0] * 4
  sign = msbin[2] & 0x80
  ieee_exp = msbin[3] - 2
  ieee[3] = sign | (ieee_exp >> 1)
  ieee[2] = (ieee_exp << 7) | (msbin[2] & 0x7f)
  ieee[:2] = msbin[:2]

  return struct.unpack('f', ieee)[0]

如果这有问题，您能举一些输入值和预期结果的例子吗？

修改：如果它是你想要的反向功能，它应该是：

def float2mbf4byte(f):
  ieee = struct.pack('f', f)
  msbin = [0] * 4
  sign = ieee[3] & 0x80

  msbin_exp = (ieee[3] << 1) | (ieee[2] >> 7)
  # how do you want to treat too-large exponents...?
  if msbin_exp == 0xfe: raise OverflowError
  msbin_exp += 2

  msbin[3] = msbin_exp
  msbin[2] = sign | (ieee[2] & 0x7f)
  msbin[:2] = ieee[:2]
  return msbin

Answer 2

好吧，我尝试了float2mbf4byte()并做了两次修改：

正在转换负值，
对于Python 2，ieee应该是int的列表，而不是字符串

摘录：

def float2mbf4byte(f):
    ieee = [ord(s) for s in struct.pack('f', f)]
    msbin = [0] * 4

    sign = ieee[3] & 0x80
    ieee[3] &= 0x7f

    msbin_exp = (ieee[3] << 1) | (ieee[2] >> 7)
    # how do you want to treat too-large exponents...?
    if msbin_exp == 0xfe: raise OverflowError
    msbin_exp += 2

    msbin[3] = msbin_exp
    msbin[2] = sign | (ieee[2] & 0x7f)
    msbin[:2] = ieee[:2]
    return msbin

def ieee2fmsbin(f):
    return struct.pack('4B', *float2mbf4byte(f))

Answer 3

mbf2ieee无法正确转换，请尝试以下操作：

import struct

def float2mbf4byte(f):
    ieee = struct.pack('f', f)
    msbin = [0] * 4
    sign = ieee[3] & 0x80

    msbin_exp = (ieee[3] << 1) | (ieee[2] >> 7)
    # how do you want to treat too-large exponents...?
    if msbin_exp == 0xfe: raise OverflowError
    msbin_exp += 2

    msbin[3] = msbin_exp
    msbin[2] = sign | (ieee[2] & 0x7f)
    msbin[:2] = ieee[:2]
    return msbin

def mbf2ieee(mbf_4bytestring):
    msbin = struct.unpack('4B', mbf_4bytestring)
    if msbin[3] == 0: return 0.0

    ieee = [0] * 4
    sign = msbin[2] & 0x80
    ieee_exp = msbin[3] - 2
    ieee[3] = sign | (ieee_exp >> 1)
    ieee[2] = (ieee_exp << 7) | (msbin[2] & 0x7f)
    ieee[:2] = msbin[:2]

    return struct.unpack('f', bytearray(ieee))[0]


print(mbf2ieee(bytearray(float2mbf4byte(52400126))))

...，您将得到：

builtins.ValueError：字节必须在范围（0，256）中因为正确的答案是[0,E4,47,9A]，但是 float2mbf4byte给出[0, 228, 19527, 76]。第三个元素不是字节大小值

如何将IEEE Python float转换为Microsoft Basic float

3 个答案: