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Hi All
Hopefully someone can help shed some light for me.
I have some code I have used for years to calculate and store (in SQL Server database), and retrieve and compare a hash value using ComputeHash of the MD5CryptoServiceProvider. I have recently upgraded to x64 (Windows 7) from x86 (Vista) but now my hashes calculated on the x86 does not match when compared (using x64)! (Hope that all makes sense.)
Is there any obvious reasons for this? Where should I be looking??
thanx
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Well, I think I have narrowed it down to the "GetHashCode" being the culprit! After replacing the "GetHashCode" with my own hash function it seems to work in both x86 and x64 OSs.
For Each c As DataColumn In ds.Tables("mytable").Columns
If Not c.ColumnName = "hashvalue" Then
If r(c) IsNot DBNull.Value Then RowHash += r(c).GetHashCode.ToString
End If
Next
' ... compare the "RowHash" with the one stored in the "hashvalue" column ...
This article seem to agree.
"... the .NET Object.GetHashCode() method, which unfortunately differs between x86 and x64 systems."
Any have any clue why?? That sucks (nothing in the documentation)!
modified on Wednesday, August 19, 2009 3:47 AM
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I believe that Microsoft's documentation for GetHashCode specifies that no assumption should be made about the value returned, other than the fact that within a given execution context, if a=b, a.GetHashCode=b.GetHashCode. The release of a class with one version of GetHashCode does not imply a contract that all versions of the class will yield the same GetHashCode; indeed, there may be good reasons why future versions would not.
For example, someone might have a class to store shapes, using a fairly simple GetHashCode implementation, and then discover that some particular application which stores shapes in a hash table performs poorly because many different shapes evaluate to the same hash. If the release of the earlier version of GetHashCode compelled all future versions to perform identically on those shapes, it would be impossible to fix its poor behavior with certain combinations of shapes. Allowing GetHashCode to change avoids this risk.
Further, I would expect that an object's implementation would even be allowed to have an object's hash code vary based upon the circumstances in which it, or the first still-existing object like it, was created. For example, an object holds a strings could, every time the string is modified, check for it in a dictionary and either use or add a dictionary reference. If all matching strings would use the same dictionary reference, the object's GetHashCode could use the hash of that dictionary reference rather than computing the actual hash of the string, even though the hash of the dictionary reference would be affected by when the object was first inserted.
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Thank you for your comment.
I agree, between versions (or even builds) an implementation should be allowed to change and also to change its return value. But here we are talking about exactly the same "implementation" (of the method) behaving on differently depending on the platform/CPU (x86 vs x64). As much as your comment makes sense, I can't see how it applies to the same implementation across CPU - am I missing something?
PS: The "sucks" was just venting my frustration  as my newly found wisdom has caused me quite an substantial bit of extra work 
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But here we are talking about exactly the same "implementation" (of the method) behaving on differently depending on the platform/CPU (x86 vs x64).
How do you know that it's really the same implementation? I don't know what operations Microsoft's x86 version of .GetHashValue does for different operand types, but if it uses some operations which are efficient on the x86 and less efficient on x64, or fails to use operations which would be more efficient on the x64, would you want Microsoft to use an inefficient version of .GetHashValue for the x64 versions of .net, or should it use efficient ones?
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"would you want Microsoft to use an inefficient version of .GetHashValue for the x64 versions of .net, or should it use efficient ones?"
...it depends on how it affects me 
oh well, for me, a nuisance thats all - thanks for enlightening me! 
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francoisdotnet wrote: Where should I be looking??
You should be looking in the documentation[^] which makes it very clear that hash values are not fixed from one environment to the next, and cannot be shared between systems. Their sole purpose is to speed up things on one machine by providing a reasonable hash value as fast as possible.
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get.
Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
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I have a loop at the moment that creates a number loop that is 5 deep, each number in a sequence can only be used once...for example
12345
12354
12435
54321 etc...
Here is what i have for the code creating this sequencing...
SortOrder = New List(Of Integer())
Dim iTemp(PanelDepth) As Integer, iCount As Integer = 0
For a As Integer = 0 To PanelDepth - 1
For b As Integer = 0 To PanelDepth - 1
If b <> a Then
For c As Integer = 0 To PanelDepth - 1
If c <> b And c <> a Then
For d As Integer = 0 To PanelDepth - 1
If d <> c And d <> b And d <> a Then
For e As Integer = 0 To PanelDepth - 1
If e <> d And e <> c And e <> b And e <> a Then
ReDim iTemp(PanelDepth)
iTemp(0) = a
iTemp(1) = b
iTemp(2) = c
iTemp(3) = d
iTemp(4) = e
SortOrder.Add(iTemp)
End If
Next
End If
Next
End If
Next
End If
Next
Next
my dilemma is that i need it to be variable on the depth of the sequencing, so for example i might need it to calculate 9 deep, so 123456789, or even more 10/11 sometimes, but i am having trouble coming up with a way to do this, anyone got some ideas that i could try to get it to loop through and still create individual number sets for a <i>n</i> deep sequence?
ta.
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Please don't cross post messages. While this is the original post (based on time) the one that has actually received answers is here[^].
Scott Dorman Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA
[ Blog][ Articles][ Forum Guidelines]
Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai
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The solution is to use a recursive algorithm that gives all the permutations of a list of elements, regardless of the size.
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I already know about algorithms for traversing trees . I need to traverse a tree and recognize some kind of nodes . For example I want to know if a node is the last child of its far parent.It means the node which has no children and no one of its siblings has any child and also this node must be the last node in terms of its sibilings. How can I recoginze such a node in a recursive function ?
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I'm not sure if this is exactly what you need, but I was thinking along the lines of a modified breadth-first search[^] algorithm:
1) Enqueue all the children of your parent node, setting their depth to 1 (or 0).
2) Examine the next node in the queue.
3) If it has children, enqueue all children, setting their depth to the depth of their parent + 1, and dequeue the node.
4) If it has no children, leave it in the queue.
5) When you have only childless nodes in the queue (i.e. you don't have a next node to process), proceed to step 6, otherwise go back to step 2.
6) Your queue now contains all childless nodes, and those with higher depth are the ones you are looking for.
7) Examine all nodes with higher depth and determine which is the "last node in terms of its siblings" (I guess you have some specific node property to do this ?)
Hope it can be of some help.
2+2=5 for very large amounts of 2
(always loved that one hehe!)
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How can i calculate time complexity and space complexity?
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Calculating time complexity for an algorithm means getting an estimate of the number of cycles it must undergo in order to solve the problem.
As a very simple example, a dumb search algorithm on a vector of size n will have time complexity O(n), since it will go through all the vector's cells to find the key - the "big O" indicates the order of time complexity, and is the standard way of writing time complexity.
On the other hand, a binary search will have time complexity O(log2 n), since it will divide the vector in two at each cycle.
Calculating all permutations of a given set of items has time complexity O(n!) (NP-Complete class of time complexity), and so on.
The same goes for calculating space complexity (EDIT: what I mean is if you use for example only a vector of length n, then the space complexity is n, and so on.).
Have a look here[^] for more info. 
2+2=5 for very large amounts of 2
(always loved that one hehe!)
modified on Friday, August 14, 2009 2:18 PM
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i need more explanation
how can we calculate o(n), o(n2),o(nlogn)
if i have one problem, hoe can i calculate like that
and also space complexity
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I need some guides from you.
I want to know whether HMM or Markov model is the right choice for target tracking.
I want to choose a method or an algorithm using vc++ to realize target tracking.
Or which method is good for doing this project?
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For tracking try googling phrases such as:
1. particle filter
2. mean-shift
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Thank you for your care. I have found out that there are many articles concerned about particle filter and mean-shift.
But I wanna figure out whether I can use Markov or HMM to finish this project.
It seems that there are only a few papers which use these stochastic method.
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superwave wrote: It seems that there are only a few papers which use these stochastic method.
Funny, I did a pretty restrictive Google search and got over 1400.
Google It[^]
You measure democracy by the freedom it gives its dissidents, not the freedom it gives its assimilated conformists.
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Thank you for your help.
modified on Monday, August 10, 2009 12:40 AM
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Dear Sir/Madam,
Me Rakesh Ranjan Dey,Software Engineer,working at software company and also doing M Tech in Computer Sc. & Eng.I have to do a project named structured data extraction that wiil extract data from web and put into database.I have to create a DOM tree for a particular web page.So I am requesting you to guide me about how to create DOM tree with some useful code to extract structured data extraction from web so that I will be thankful to you.
Rakesh Ranjan Dey
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Hi people, i am doing some 'while' loop but kinda stuck somewhere.
What i want to do is actually is comparing from 2 database tables.
The problem now is example i have 10 records in SMS_IN table, but my code only runs the first record everytime i calls it. By right, it should loop thru all the data and check.
SMS_IN (sample data)
originator | text | date
88411254 | Internet bla bla bla | 5 August
78412447 | Quiz ans1 ans2 ans3 | 5 August
USERAPP (sample data)
userid | keyword
54 | Internet
80 | Quiz
So the logic is first it will check the SMS_IN text column, example the first word of the first result is 'Internet', then it will check the USERAPP keyword column, if the keyword 'Internet' exists, means its a valid sms. If the keyword does not exists at all in the USERAPP table, the msg will be deleted from SMS_IN table
this is my code
ResultSet rs = null;
ResultSet rs2 = null;
String sql = "Select * from smsserver_in";
String sql1 = "Select * from USERAPP";
rs = db.SelectDB(sql);
rs2 = db.SelectDB(sql1);
try {
String firstword = null;
String keyword = null;
int number = 0;
while (rs.next()) {
StringTokenizer st = new StringTokenizer(rs.getString("text"));
firstword = st.nextToken();
number = rs.getInt("id");
while (rs2.next()) {
keyword = rs2.getString("keyword");
if (firstword.equals(keyword)) {
out.println(number);
String sql3 = "Insert into app_" + keyword + "(originator,text)values(" + rs.getString("originator") + ",'" + rs.getString("text") + "')";
db.InsertDB(sql3);
String sql4 = "delete from smsserver_in where id=" + number;
db.UpdateDB(sql4);
} else {
}
}
}
} catch (Exception ex) {
}
}
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Hi,
your code is wrong, it has two nested loops but acts as if there were only one loop.
Here is a very simple snippet with the same problem, it should help you in understanding what goes wrong:
int i1=0;
int i2=0;
for (; i1<10; i1++) {
for (; i2<10; i2++) {
Console.WriteLine("i1="+i1+" i2="+i2);
}
}
Now imagine you executing this code by hand.
If you still don't see it, run the code. Then use the debugger, set a breakpoint, and learn.
If you discover this, chances are you won't make the same mistake ever again.
Luc Pattyn [Forum Guidelines] [My Articles]
The quality and detail of your question reflects on the effectiveness of the help you are likely to get.
Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
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Okay, anyway my loop is working already, but just some problems.
At which part should i add the code to delete the message after checking thru all the keywords and it does not match?
I tried adding a else statement inside the if statement of my inner loop but its not working
ResultSet rs = null;
ResultSet rs2 = null;
try {
String firstword = null;
String keyword = null;
int number = 0;
String sql = "Select * from smsserver_in";
rs = db.SelectDB(sql);
while (rs.next()) {
StringTokenizer st = new StringTokenizer(rs.getString("text"));
firstword = st.nextToken();
number = rs.getInt("id");
String sql1 = "Select * from USERAPP";
rs2 = db.SelectDB(sql1);
while (rs2.next()) {
keyword = rs2.getString("keyword");
if (firstword.equals(keyword)) {
out.println(number);
String sql3 = "Insert into app_" + keyword + "(originator,text)values(" + rs.getString("originator") + ",'" + rs.getString("text") + "')";
db.InsertDB(sql3);
String sql4 = "delete from smsserver_in where id=" + number;
db.UpdateDB(sql4);
}
}
}
} catch (Exception ex) {
}
modified on Tuesday, August 4, 2009 11:37 PM
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