Newbie lost(new info)

[Anton Vredegoor]

Angelo Secchi <secchi at sssup.it> wrote:

>>from binascii import hexlify
>>inf = file('foo','rb')
>>data = inf.read(1970)
>>for i in range(223):
>>     index = i * 4 + 113
>>     print hexlify(data[index: index + 4])
>
>
>46ee3bb4	(I know that this should be 15612852)
>00000000	(I know that this should be 0)
>00000000	(I know that this should be 0)
>465de39a	(I know that this should be 6153114)
>00000000	(I know that this should be 0)
>00000000	(I know that this should be 0)

Based on this message:

http://groups.google.com/groups?&selm=1993Aug25.074420.28786%40bhof01.ctg.nl

I wrote a function that maybe could do it (use at own risk). It
converts  a 4-byte real from "IBM System/370 Floating Point Format" to
a Python float. In your code above replace one line:

>>     print hexlify(data[index: index + 4])

with:

>>     print ibm370tofloat(data[index: index + 4])


The conversion function and a test function:

import struct

def ibm370tofloat(fourbytes):
    i = struct.unpack('>I',fourbytes)[0]
    sign = [1,-1][bool(i & 0x100000000L)]
    characteristic = ((i >> 24) & 0x7f) - 64
    fraction = (i & 0xffffff)/float(0x1000000L)
    return sign*16**characteristic*fraction   

def test():
    import binascii
    pi = "413243f7"
    s1 = "46ee3bb4"
    s2 = "465de39a"
    for x in [pi,s1,s2]:
        y = binascii.unhexlify(x)
        print ibm370tofloat(y)

if __name__=='__main__':
    test()

output:

3.14159297943
15612852.0
6153114.0

I hope this helps.

Anton