Newbie lost(new info)

[Howard Lightstone]

Angelo Secchi <secchi at sssup.it> wrote in 
news:mailman.150.1077786326.8594.python-list at python.org:

> 
> John and Anthon thanks for your help.
> If I did it correctly this is the outcome of the code you asked me to
> try:
> 
>>from binascii import hexlify
>>inf = file('foo','rb')
>>data = inf.read(1970) # 1970 is the exact length of the line
>>for i in range(4):   
>>     index = i * 32
>>     print hexlify(data[index: index+32])
> 
> 
> 3131313131313131312030313032323230313033343130323238353332303031
> 3220202020203032323835333230303132303030303031303030303030314338
> 3930303030303120203939333531302030313130303030312020313220313335
> 313030313032323230313033343133343146ee3bb40000000000000000465de3
> 
> 
> 
>>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)
> ...


I seem to recall that the format is 
   sCCCCCCC MMMMMMMM MMMMMMMM MMMMMMMM

The CCCCCCC exponent is biased by 64 and is HEX  (16**(CCCCCCC-64)).

I recall significance issues on Gould machines because the normalization 
was only to the nibble so there might be 2 or 3 0-bits in the mantissa.

41100000   was 1.0

My sample code:

import struct

dividend=float(16**6)

def fromhex370(invalue):
    "convert 4 char binary string 370-formatted floating point float value"
    if invalue == 0:
        return 0.0
    istic,a,b,c=struct.unpack('>BBBB',invalue)
    if istic >= 128:
        sign= -1.0
        istic = istic - 128
    else:
        sign = 1.0
    mant= float(a<<16) + float(b<<8) +float(c)
    return sign* 16**(istic-64)*(mant/dividend)

Of course, no optimation was even thought of ......

I believe the long floating point format just added 4 more bytes of 
significance to the end of the 4 bytes I mentioned above.

HTH