Problem

[Patrick]

Hi,

This is actually a VB 6.0 query, not VB.NET. I posted it in VB NG but did not get a reply..hopefully I will get some help out here..

-------------
Whenever i test the follwing, an Overflow error -6 occurs

sun test()

dim L as long

dim D as double

dim result as double

L=12112 'any value

D=2^31

result= L and D

result= L or D

result= L or(not D)

end sub

It seems that the bitwise operator "or,Xor,And,Not" may not work on 32bit number with signbit? Please give some solution.

 

[Cor]

Hi Patrick or is it Gary,
The same thread is in this newsgroup.
This one of the favorite questions for Fergus,
So there are very nice answers at Gary.
Cor

 

[Fergus Cooney]

Hi Patrick,

As Cor says, this has been answered already.

If you are Gary, posting under the topic: Help!, then you know what I'm
talking about.

If you are Patrick, a different person to Gary, but with exactly the same
query!!, do a search for 2^31 and you will find the other question and the
answers.

Regards,
Fergus

 

[Fergus Cooney]

Hi again,

Again, if you are Gary, you posted a query about serialization, topic:
Advice needed !. That has also been answered. I have added a footnote
containing 2^31 so that the same search will find it.

;-)

As an aside:
Almost all the queries we get are from people with a 'problem' who
need some 'help' and 'advice' - whatever those words might mean at the time.
Can I recommend that you use titles that convey some information to us
as query responders and also to those who search the newsgroups for topics
that might help them?

Regards,
Fergus

 

[Jay B. Harlow [MVP - Outlook]]

Fergus,
I suspect its the same homework assignment! ;-)

Of course with VB.NET 2003 Gary Patrick can use the new bit shift operator &
safe the expense of the exponent & the doubles!

Sub Test()
Dim L As Integer
Dim D As Integer
Dim result As Integer

L = 12112 'any value
D = 1 << 31
result = L And D
result = L Or D
result = L Or (Not D)
End Sub

Which BTW works correctly on the sign bit!

Jay

 

[Cor]

Hi Jay B,
That's it, clever,
LOL
Cor

 

[Fergus Cooney]

Hi Jay,

Now <that's> handy - I hadn't discovered (or registered, perhaps)
bit-shifting in VB.NET.

Finally! some attention to bits and bytes. Now all we need is an unsigned
type, perhaps, and a bit more work on casting Longs with 'Int' sign-bits.

Regards,
Fergus

 

[Jay B. Harlow [MVP - Outlook]]

Fergus,
Just note, you need VB.NET 2003 (.NET 1.1) for bit shifting.

VB.NET 2004 (.NET 2.0) we are suppose to get unsigned types.

http://msdn.microsoft.com/vstudio/productinfo/roadmap.aspx

perhaps, and a bit more work on casting Longs with 'Int' sign-bits.

Are you saying you want:

Dim l As Long = 1L << 31
Dim i As Integer = CInt(l)

Where you get a negative number instead of overflow?

You can use System.BitConverter:

Dim l As Long = 1L << 31
Dim i As Integer

Dim bytes() as Byte
bytes() = BitConverter.GetBytes(l)
i = BitConverter.ToInt32(bytes, 0)

There may be a 'more efficient' way, that I'm not thinking of, but the above
works ;-)

Of course the above effectively truncates the high order half of the long.

Or are you thinking something else?

Hope this helps
Jay

 

[Fergus Cooney]

Hi Jay,

Ha!. When I read about VB bit-shifts in your post I thought I must be
getting tired. I've spent the weekend converting a calculator from QBasic (of
all things) to .NET so I was studying operator precedence and expression
grammar. Never saw bit shifts. LOL. Of course I hadn't discovered them - I've
got v1.0 and the corresponding Help.

!! ... negative number instead of overflow?

Yes, that's the chap. In days gone past it could be done using Peek and
Poke, LSet-ing a string into a random-access file's buffer and reading an Int
out, and all sorts. Thanks for the BitConverter - that's the VB.NET
workaround, eh? Lol. It beats doing Long to bytes, bytes to string (Unicode
BigEndian), string to bytes (LittleEndian), bytes to Int (I know,.. joke).

I'd read the C# roadmap but not the VB one. I look forward to operator
overloading - every class should have at least one!! (I know,.. joke).
Partials and generics will be good, though. Roll on 2004 and unsigned types. I
hope they're more useful that the C# ones which seem to need more casting than
a war movie.

Cheers,
Fergus

 

[Gary]

Hi Fergus,

Thanks for the reply.

I am sorry for using such *meaningless* subjects, your point taken ... yes I
need to provide some info. in the subject line so that
people can get some idea about the problem.

Thanks all, for all your wonderful replies

- Gary -