Prevent wildcards from being accepted in filenames (NT mode)

[Shachar Shemesh]

Dimitrie O. Paun wrote:

>On November 26, 2003 11:22 pm, Dmitry Timoshkov wrote:
>  
>
>>(GetVersion() & 0x80000000)==0) construct is very inefficient. It forces
>>compiler generate both a bit mask test and a comparison operation. While
>>many modern processors have very effective bit test instructions, and
>>we have to tell to the compiler that we want only a bit test.
>>
>>Simple !(GetVersion() & 0x80000000) is much better IMO.
>>    
>>
>
>Do you honestly think that a compiler can't figure out this is the
>same thing?!? Even if it didn't, you'd be hard pressed to even measure
>such minute differences, so no, it's not very inefficient by any means.
>  
>
...

>So while I prefer your version for stylistic reasons, I can't agree
>with the spirit of the complaint.
>  
>
Something that does affect efficiency, which I debated with myself for 
some time, is the order of the tests. As the "if" is, by far, much more 
likely to be false than true, we should order the condition using a cost 
function that takes into account how much each condition costs to test, 
and how likely it is to fail (as that's the case wer'e trying to 
optimize - we don't really care how long it's going to take in case the 
"if" is true).

My original gut feeling was to place the conditions in reverse order. 
That is, first test for version, only then test whether there are any 
wildcards in the string. The reason I submitted it as I did was that the 
first attempt would not work. It appears that "DOSFS_GetFullName" is 
called before the structs needed for "GetVersion" to function are 
initialized. As such, reversing the order was necessary to make it work 
(that, or insert complicated changes throughout the entire kernel 
initialization).

In retrospect, this form is better. GetVersion is not a simple function, 
and is far less likely to fail than strchr. I guess ideal would be to 
have a global inside kernel.dll that tells us whether wer'e NT or not. 
There is no such global at the moment, however, and I did not wish to 
introduce one.

-- 
Shachar Shemesh
Open Source integration & consulting
Home page & resume - http://www.shemesh.biz/