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QMid <-> DWORD conversion

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Last days i studied the article on fsdev wiki here:
http://www.fsdeveloper.com/wiki/index.php?title=BGL_File_Format#Getting_DWORD_values_from_QMID
I originally found it very hard to understand (I am not native speaker and I was not good in mathematics in my school days). So I added some explanations and tables to the conversions between numeral systems used in the conversion.

But still the rest of the article seems to me very unclear. It's not clear where the author takes the input variables and what type of conversion he did when he did the examples.

So I ask here, if anybody here understands the final conversion. Clarify to me and I will update the article to be more clear.

The part which I have problem to grasp:

1819 = 0x71B and 1012 = 0x3F4.
so U0 = 0x1B, U1 = 0x07, V0 = 0xF4 and V1 = 0x03. Other values are 0x00.
The conversion gives:
U'0 = 0x145, U'1 = 0x15, V'0 = 0x5510 and V'1 = 0x05. Other values are 0x00.

What conversion he used to convert hexadecimal number 0x1B to hexadecimal number 0x145?
 
I have updated the page,
but I am not sure if this is correct:
Code: 
b = (hexadecimal) 1 0 4 5
y = 1*4^4 + 0*4^3 + 4*4^1 + 5*4^0
Author has there:
  • ai = 0 ⇒ bi = 0
  • ai = 1 ⇒ bi = 1
  • ai = 2 ⇒ bi = 4
  • ai = 3 ⇒ bi = 5
and his calculation:
Let's have b3 = 1, b2 = 0, b1 = 4, b0 = 5 and the output value is: 1 x 4096 + 0 x 256 + 4 x 16 + 5 = 4165
Click to expand...
that does not correspond with exponents 0,1,4,5
 
1,0,4,5 not 0,1,4,5

Please don't change the wiki articles unless you truly understand what you are doing!
 
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rhumbaflappy said:
1,0,4,5 not 0,1,4,5

Please don't change the wiki articles unless you truly understand what you are doing!
Click to expand...

I did not changed anything from the authors text I just added to it to make things more clear. Also arno said everybody can contribute there.

I think you missunderstand me. The text I quoted was from the original article, not from changes made by me!

Also, you do not follow what I asked. What is this table:
  • ai = 0 ⇒ bi = 0
  • ai = 1 ⇒ bi = 1
  • ai = 2 ⇒ bi = 4
  • ai = 3 ⇒ bi = 5
it represents exponents not the digits to be multiplied. Hence I ask why this does not correspond the formula. Maybe he has a mistake there and should be 0,1,3,4 this would make sense. I don't know if anybody here realized the the really big problem, that somebody written article which was not clear because it was missing clear descriptions of what he is doing and descriptions of the formulas. If one cannot understand it but only experts can, then what is the wiki articles for? For whom? I think this should be for everybody and not just for experts.
 
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Seriously. If you do not understand the subject, why do you think you can contribute to it, add to it, or change it? We have forums to use for questions about the wiki articles. Please use these forums and leave the wiki articles alone if you do not understand them.

You can really mess up someone's understanding of articles if you change or add to them without some sort of understanding of the subject. The original author could rewrite portions of the wiki article if it is wrong, and you point it out. As far as your ability to understand an article, that is a common problem for all of us when reading unfamiliar subjects. You are right in using the forums for help in gaining a clearer understanding. You are not right in altering a wiki article because you cannot comprehend it.

I would strongly suggest you undo the alterations you made to the wiki article. And yes, anyone can contribute an article. But no one should alter other's articles without a thorough understanding of the subject.

Dick
 
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