Does any one recognize this binary data storage format

[John Machin]

Bengt Richter wrote:
> On Tue, 09 Aug 2005 21:50:06 -0000, Grant Edwards <grante at visi.com> wrote:
> 
> 
>>On 2005-08-09, Scott David Daniels <Scott.Daniels at Acm.Org> wrote:
>>
>>>Grant Edwards wrote:
>>>
>>>>>Ex #1)   333-3333
>>>>>Hex On disk: 00 00 00 80 6a 6e 49 41
>>>>>
>>>>>Ex #2) 666-6666
>>>>>Hex On disk: 00 00 00 80 6a 6e 59 41
>>>>
>>>>So there's only a 1-bit different between the on-disk
>>>>representation of 333-3333 and 666-6666.
>>>>
>>>>That sounds pretty unlikely.  Are you 100% sure you're looking
>>>>at the correct bytes?
>>>
>>>Perhaps the one bit is an exponent -- some kind of floating point
>>>based format?  That matches the doubling of all digits.
>>
>>That would just be sick.  I can't imagine anybody on an 8-bit
>>CPU using FP for a phone number.
>>
>>-- 
>>Grant
>>
> 
>  >>> def double_binary_lehex_to_double(dhex):
>  ...     "convert little-endian hex of ieee double binary to double"
>  ...     assert len(dhex)==16, (
>  ...         "hex of double in binary must be 8 bytes (hex pairs in little-endian order")
>  ...     dhex = ''.join(reversed([dhex[i:i+2] for i in xrange(0,16,2)]))
>  ...     m = int(dhex, 16)
>  ...     x = ((m>>52)&0x7ff) - 0x3ff - 52
>  ...     s = (m>>63)&0x1
>  ...     f = (m & ((1<<52)-1))|((m and 1 or 0)<<52)
>  ...     return (1.0,-1.0)[s]*f*2.0**x
>  ...
>  >>> double_binary_lehex_to_double('000000806a6e4941')
>  3333333.0
>  >>> double_binary_lehex_to_double('000000806a6e5941')
>  6666666.0
>  >>> double_binary_lehex_to_double('0000108777F9Fc41')
>  7777777777.0
> 
> ;-)
> 
> Regards,
> Bengt Richter

Well done, Scott & Bengt!!
I've just verified that this works with all 12 corrected examples posted 
by the OP.

Grant, MS-DOS implies 16 bits at least; and yes there was an FPU (the 
8087). And yes there are a lot of sick people who store things as 
numbers (whether integer or FP) when the only arithmetic operations that 
can be applied to them stuff them up mightily (like losing leading 
zeroes off post-codes, having NEGATIVE tax file numbers, etc) and it's 
still happening on the best OSes and 64-bit CPUS. Welcome to the real 
world :-)

Cheers,
John