[RESOLVED] Efficiency Comparison of Nested Ifs ??

[ThatSamiam]

Hi,

A general question: which is more efficient?
(Assume case statements, etc., cannot be used.)

    If a Then
      If x Then
        ax()
      ElseIf y Then
        ay()
      End If

    ElseIf b Then
      If x Then
        bx()
      ElseIf y Then
        by()
      End If

    ElseIf c Then
      If x Then
        cx()
      ElseIf y Then
        cy()
      End If

    End If

-- or --

    If a AndAlso x Then
      ax()
    ElseIf a AndAlso y Then
      ay()
    ElseIf b AndAlso x Then
      bx()
    ElseIf b AndAlso y Then
      by()
    ElseIf c AndAlso x Then
      cx()
    ElseIf c AndAlso y Then
      cy()
    End If

[formlesstree4]

Easiest way to find out: place a stopwatch at the beginning and end of each type and time them.

[ThatSamiam]

Yeah. Why didn't I just time it?

The AndAlso-ed code is >20% faster than the nested code.


Nested AndAlso-ed Diff
1 421.8615 359.3635 62.498
2 437.486 328.1145 109.3715
3 437.486 328.1145 109.3715
4 390.6125 328.1145 62.498
5 406.237 343.739 62.498
6 406.237 328.1145 78.1225
7 390.6125 343.739 46.8735
8 390.6125 328.1145 62.498
9 406.237 328.1145 78.1225
10 390.6125 328.1145 62.498
11 421.8615 328.1145 93.747
12 437.486 343.739 93.747

ave 411.4451667 334.6247083 76.82045833

Faster by 22.95719844 %

(Hmm..., tables don't paste well.)

  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim a, b, c, x, y As Boolean
    Dim i As Integer
    Dim d As Date

    d = Now
    For i = 0 To 12000000
      If i = 3000000 Then c = True
      If i = 6000000 Then b = True
      If i = 9000000 Then a = True

      If i = 1000000 Then y = True
      If i = 2000000 Then x = True
      If i = 3000000 Then x = False : y = False
      If i = 4000000 Then y = True
      If i = 5000000 Then x = True
      If i = 6000000 Then x = False : y = False
      If i = 7000000 Then y = True
      If i = 8000000 Then x = True
      If i = 9000000 Then x = False : y = False
      If i = 10000000 Then y = True
      If i = 11000000 Then x = True

      If a Then
        If x Then
          ss()
        ElseIf y Then
          ss()
        End If

      ElseIf b Then
        If x Then
          ss()
        ElseIf y Then
          ss()
        End If

      ElseIf c Then
        If x Then
          ss()
        ElseIf y Then
          ss()
        End If

      End If
    Next

    TextBox1.Text &= (Now - d).TotalMilliseconds.ToString & vbCrLf


    d = Now
    For i = 0 To 12000000
      If i = 3000000 Then c = True
      If i = 6000000 Then b = True
      If i = 9000000 Then a = True

      If i = 1000000 Then y = True
      If i = 2000000 Then x = True
      If i = 3000000 Then x = False : y = False
      If i = 4000000 Then y = True
      If i = 5000000 Then x = True
      If i = 6000000 Then x = False : y = False
      If i = 7000000 Then y = True
      If i = 8000000 Then x = True
      If i = 9000000 Then x = False : y = False
      If i = 10000000 Then y = True
      If i = 11000000 Then x = True

      If a AndAlso x Then
        ss()
      ElseIf a AndAlso y Then
        ss()
      ElseIf b AndAlso x Then
        ss()
      ElseIf b AndAlso y Then
        ss()
      ElseIf c AndAlso x Then
        ss()
      ElseIf c AndAlso y Then
        ss()
      End If
    Next

    TextBox2.Text &= (Now - d).TotalMilliseconds.ToString & vbCrLf

  End Sub

  Sub ss()

  End Sub

[formlesstree4]

So is this resolved...?

[ThatSamiam]

Yeah, its resolved. I will mark it as such.