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Message from discussion Extract double in binary file
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Bengt Richter  
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 More options Dec 2 2003, 5:17 pm
Newsgroups: comp.lang.python
From: b...@oz.net (Bengt Richter)
Date: 2 Dec 2003 22:17:42 GMT
Local: Tues, Dec 2 2003 5:17 pm
Subject: Re: Extract double in binary file
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On 2 Dec 2003 09:40:50 -0800, pascal.par...@free.fr (Pascal) wrote:

>A very big thanks to you.
>The function run perfectly (after python 2.3! installed for enumerate function)
>If you can, give me more details on the methode or the number's representation.

>Thanks a lot!

According to an old MASM 5.0 programmer's guide, there was a Microsoft Binary format
for encoding real numbers, both short (32 bits) and long (64 bits).

There were 3 parts:

1. Biased 8-bit exponent in the highest byte (last in the little-endian view we've been using)
   It says the bias is 0x81 for short numbers and 0x401 for long, but I'm not sure where that lines up.
   I just got there by experimentation.

2. Sign bit (0 for +, 1 for -) in upper bit of second highest byte.

3. All except the first set bit of the mantissa in the remaining 7 bits of the second highest byte,
   and the rest of the bytes. And since the most signficant bit for non-zero numbers is 1, it
   is not represented. But if if were, it would share the same bit position where the sign is
   (that's why I or-ed it in there to complete the actual mantissa).

MASM also supported a 10-byte format similar to IEEE. I didn't see anything in that section
on NaNs and INFs.

HTH

Regards,
Bengt Richter


 
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