best way to find out if x is a even or odd number?

[Tontow]

what is the best way to find out if x is a even or odd number?

[UserLoser.]

Code Select Expand


IsOdd = (Number Mod 2)


If if the number is odd, it returns 1, otherwise, 0

[Banana fanna fo fanna]

Or you could do:

Code Select Expand


IsEven = Not (Number Mod 2)


[K]

That seems like a really slow way to do it.  You're doing division and checking the remainder.  Why not

Code Select Expand


If Number And 1
'   odd.
End If


[Banana fanna fo fanna]

K just owned us.

[Grok]

Don't be so sure.  Depends on how you run it.

1 billion iterations:

Option Explicit

Code Select Expand

Private Sub cmdTest_Click()
   
    Dim T1 As Variant
    Dim T2 As Variant
    Dim lPos As Long, lMax As Long
    Dim Number As Long
    Dim IsOdd As Boolean, IsEven As Boolean
    Dim test As Long
   
    Number = 8391
    test = 2
   
    lMax = 1000000000
    T1 = Now
    Select Case test
    Case 0
        For lPos = 1 To lMax
            IsOdd = (Number Mod 2)
        Next
    Case 1
        For lPos = 1 To lMax
            IsEven = Not (Number Mod 2)
        Next
    Case 2
        For lPos = 1 To lMax
            If Number And 1 Then
                IsOdd = True
            End If
        Next
    End Select
    T2 = Now
    txtTime.Text = Format(DateDiff("s", T1, T2), "0") & " s"
   
End Sub

Interpreted:
Case 0:  41 seconds
Case 1:  45 seconds
Case 2:  63 seconds

Compiled (p-code):
Case 0:  40 seconds
Case 1:  37 seconds
Case 2:  18 seconds

Compiled (machine code):
Case 0:  1 seconds
Case 1:  1 seconds
Case 2:  1 seconds

Need a more accurate timer to figure out speed when compiled to machine code.

[K]

My premise was that a bitwise and is cheap, while a division operation and checking the remainder is (more) expensive.  Does it really matter if that doesn't apply when running inside the VB IDE?

[Banana fanna fo fanna]

Compiled (p-code):
Case 0:  40 seconds
Case 1:  37 seconds
Case 2:  18 seconds

How'd that happen?

[Grok]

My premise was that a bitwise and is cheap, while a division operation and checking the remainder is (more) expensive.  Does it really matter if that doesn't apply when running inside the VB IDE?

It might matter to someone testing 5 billion operations from the IDE
Seriously though, no one was complaining about your contribution, which provided a better answer.  I was merely testing the scenarios and posting the results.

$t0rm:  TheMinistered might be able to answer that.

[K]

What I want to know is how
Not (Value Mod 2)
is faster than
(Value Mod 2).
in P-Code.

[Grok]

Great question.  I do not know.  One possibility is the load time for the p-code environment accounted for the longer time for test 0.  When I ran the second and third tesst, the program was already loaded.

[Joe[x86]]

Find if its odd using your own method!

Asuming that the number is stored in Text1.Text, the Firing button is Command1, and you have a label called label1, use this code.

Code Select Expand

Private Sub Command1_Click()
Start:
Label1.Caption = "Working"
If Val(Text1.Text) > 1 Then
     Text1.Text = Val(Text1.Text - 2)
     Goto Start
Else
     If Text1.Text = "0" Then MsgBox "Even"
     If Text1.Text = "1" Then MsgBox "Odd"
     Goto Finish
End If
Finish:
Label1.Caption = "Idle"
End Sub


Going 2 by 2, this will take insanely long when large numbers are used. I will modify this code to work by 10,000s, 1,000s, 100s 10s, 8s, 6s, 4s, and 2s.

[K]

That's an...uh...intriguing way to do it.

[Magickian]

One can also bitshift then test for 0, but this is similar to and'ing and more of a pain (since you need to know the size of your data), just another method to do the same thing.