3 replies to this topic

[Novice Alex]

Hi Guys, Now got stuck with this conversion from string to single. In the netmf, there is the function CSng, but it does not work with string object. Also try use Double.TryParse, still go the exception. Any help? I know in this forum that is a piece of code in C# but I would like to see something in VB.net and I support netmf 4.2 RC3 should have include something for this.

[Novice Alex]

Hi Guys,

Instead I try to do my Str2Sng function.
below is the sample code (not completed yet, due to all the exception caused by simple function call)

#Region "Str2Single"
    Public Shared Function Str2Single(sVal As String) As Single
        Dim dblRes As Double = 0
        Dim dblTmp As Double = 0
        Dim dblFactor As Double = 0
        Dim dblFactor1 As Double = 0
        Dim iDecmialPos As Integer = 0
        Dim iPos As Integer = 0

        Str2Single = 0

        Try
            sVal = sVal.Trim

            'Locate the decimal if any
            iDecmialPos = sVal.IndexOf(".")
            
            For iPos = sVal.Length To 0 Step -1
                If iDecmialPos < 0 Then
                    dblRes += CDbl(Integer.Parse(sVal.Substring(iPos - 1, 1))) * CDbl(10 ^ (iPos - sVal.Length))
                Else
                    If iPos < iDecmialPos Then
                        dblRes += (CDbl(Integer.Parse(sVal.Substring(iPos - 1, 1))) * CDbl(10 ^ (iPos - sVal.Length)))
                    ElseIf iPos > iDecmialPos Then
                        dblTmp = Math.Pow(1, 10)
                        dblTmp = Integer.Parse(sVal.Substring(iPos - 1, 1))
                        dblFactor1 = iDecmialPos - sVal.Length + 1
                        dblFactor = Math.Pow(10, dblFactor1)
                        dblRes += dblTmp * dblFactor
                    End If
                End If
            Next
            Return CSng(dblRes)
        Catch ex As Exception

        End Try
    End Function
#End Region

From the sample code, I realise there many exception.
Take example, the Math.Pow function. Just a simple "dblTmp = Math.Pow(1, 10)" also cause exception?
What is wrong with the netmf? Did I make any mistake in my code?

Anyone tested these function in VB.NET?

[Basiclife]

Have you tried Sng.Parse("123.456") ? Also, note that conversion int to double conversion seems to be broken in 4.2 RC3 (http://forums.netdui...ble-to-integer/) so there's a chance Sng.Parse may be broken too.

[baxter]

Microsoft.Spot.Math is very limited in what it offers; basically, just sine and cosine of an integer. If you want Pow and Sqrt, you need to write your own. However, Csng will convert your string (using MF 4.2 RC1),

Imports Microsoft.SPOT
Imports Microsoft.SPOT.Hardware
Imports SecretLabs.NETMF.Hardware
Imports SecretLabs.NETMF.Hardware.NetduinoPlus
Imports System
Imports System.IO

Module Module1

    Sub Main()
        Dim s As Single = CSng("123.456")
        Debug.Print("s = " & s.ToString) ' ---> s = 123.456001
    End Sub
   
End Module

There are postings in the forum regarding math libraries. Here are a couple of reasonably efficient functions for Pow and Sqrt,

Public Function Pow(ByVal base As Double, ByVal exp As Double, ByVal eps As Double) As Double
        'REF:
        'http://stackoverflow.com/questions/3518973/floating-point-exponentiation-without-power-function

        'for: Pow(12345, 3.333, 0.000000000000001)
        'Windows calculator = 43345080833350.462136968781988806
        'Pow                = 43345080833349.852
        '---
        'For: Pow(576, 2.1351, 0.000000000000001)
        'Windows calculator = 783029.35629994585528611534553745
        'Pow                = 783029.35629995051
        '
        If (exp >= 1) Then
            Dim temp As Double = Pow(base, exp / 2, eps)
            Return temp * temp
        Else
            Dim low As Double = 0
            Dim high As Double = 1.0
            Dim sqr As Double = sqrt1(base)
            Dim acc As Double = sqr
            Dim mid As Double = high / 2

            While (Abs(mid - exp) > eps)
                'sqr = exMath.Sqrt(sqr)
                sqr = sqrt1(sqr)
                If (mid <= exp) Then
                    low = mid
                    acc *= sqr
                Else
                    high = mid
                    acc *= (1 / sqr)
                End If
                mid = (low + high) / 2
            End While
            Return acc
        End If
    End Function
    Public Function sqrt1(ByVal num As Double) As Double
        'http://openbookproject.net/thinkCSpy/ch06.html
        'for sqrt1(123456.123456)
        'Windows calculator = 351.36323577745011426077534810366
        'sqrt1              = 351.36323577745009
        Dim approx As Double = num / 2.0
        Dim better As Double = (approx + num / approx) / 2.0
        While better <> approx
            approx = better
            better = (approx + num / approx) / 2.0
        End While
        Return approx
    End Function
    Public Function Abs(x As Double) As Double
        Return If(x <= 0, -x, x)
    End Function
    Public Function Max(ByVal a As Double, ByVal b As Double) As Double
        Return If(a >= b, a, B)
    End Function

I am using MF 4.2 RC1
Baxter