问如何将IEEE Python float转换为Microsoft Basic float
EN

Stack Overflow用户

提问于 2010-02-15 18:47:40

回答 4查看 1.3K关注 0票数 3

我得到了Python的浮点值，我需要将它转换成Microsoft Basic float (MBF)格式。幸运的是，从互联网上得到了一些代码，可以做相反的事情。

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]

现在我需要逆转这个过程，但还没有成功。有什么需要帮忙的吗？

python

mbf

回答 4

Stack Overflow用户

发布于 2010-02-15 19:21:11

如果你打算在Windows下运行时执行这些转换，更快的方法可能是下载并安装mbf2ieee.exe，然后调用结果Mbf2ieee.dll提供的CVS函数(例如通过ctype)。

如果你热衷于使用纯Python语言，我认为(但我不能测试，因为手头没有MBF数字)，下面的代码可能会起作用(我刚把它从C code here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，你能给出一些输入值和预期结果的例子吗？

编辑：如果它是你想要的反向函数，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

票数 4

Stack Overflow用户

发布于 2010-08-09 15:12:59

嗯，我尝试了float2mbf4byte()，做了两个修改：

转换负值现已生效，
for Python 2，ieee应为整型列表，而不是字符串

代码片段：

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))

票数 0

Stack Overflow用户

发布于 2020-12-11 01:17:33

mbf2ieee无法正确转换，请尝试以下命令：

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))))