将十六进制字符串转换为整数

Visual Basic 2010：最近在我的一个项目中，我的任务是读取十六进制的几个数据字段。每个字段长三个字符。所以这就是我一直在做的：

'Read the hex value and convert it to decimal
Dim hexVal as string  = "38D"
Dim intVal as integer = Convert.ToInt32(hexVal, 16)

'The integer result gets multiplied by a scaling factor
'(this is set by the manufacturer for each field).
Dim fac as single  = 200
Dim final as single  = intVal * fac
Debug.Print (final)

除了在这种情况下之外，这一直很好用：hexVal =“ FFD”和fac = 32 .NET给我intVal = 4093和final = 130976。但是，我要检查的旧系统给出-96。

我有点困惑，但可以认为它是十六进制表示法。我只有原始数据状态的文档：字符是按ISO字母No 5编码的，每个字符使用7位，即不添加奇偶校验位。三个这样的字符将构成每个32位字的字段。

我转换不正确吗？

附录：我研究了字段的定义，发现几乎所有的字段都是肯定的（或未签名的）。可以是负数或正数（带符号）。查看旧版代码，他们为每个十六进制字段计算一个未签名的结果和一个签名的结果。如果期望该字段始终为正，则他们使用无符号结果。现在，如果期望该字段为负或正，则他们将采用未签名的结果；如果高于上限，则将使用已签名的结果，否则将使用未签名的结果。到目前为止，以下是我的摘要：

    Dim hexVal As String, res As Single, decCeiling As Single
    Dim paddedHex1 As String, intVal1 As Integer = 0, resVal1 As Single = 0
    Dim paddedHex2 As String, intVal2 As Integer = 0, resVal2 As Single = 0
    Dim IsUnsignedInput As Boolean

    hexVal = "FB1"   'Raw hex input (in this case represents temperature in deg C)
    res = 0.125      'A resolution factor. Used to scale the decimal to a real-world nummber
    decCeiling = 150 'The maximum temperature we can expect is 150 degree Celcius
    IsUnsignedInput = False 'Is field unsigned or signed (for temps we can expect negative and positive)
    If hexVal.Length > 8 Then
        Throw New Exception("Input '" & hexVal & "' exceeds the max length of a raw input. The max is 8 characters.")
    EndIf

    'This calcualtion assumes an unsigned value (that is, always a positive number)
    paddedHex1 = hexVal.ToString.PadLeft(8, CChar("0"))
    intVal1 = Convert.ToInt32(paddedHex1, 16)
    resVal1 = intVal1 * res

    'This assumes a signed value (that is, could be a negative OR positive number.
    'Use two's complement to arrive at the result.
    paddedHex2 = hexVal.PadLeft(8, CChar("F"))
    Dim sb As New StringBuilder(paddedHex2.Length)
    For i As Integer = 0 To paddedHex2.Length - 1
        Dim hexDigit As Integer = Convert.ToInt32(paddedHex2(i), 16)
        sb.Append((15 - hexDigit).ToString("X"))
    Next i

    Dim inverted As Integer = Convert.ToInt32(sb.ToString, 16)
    intVal2 = -(inverted + 1)
    resVal2 = intVal2 * res

    'Finally, which result do we use as the final decimal? For our example we get
    'resVal1 (unsigned)=+502.125
    'resVal2 (signed)  =  -9.875
    'Field is signed so is 502.125 > 150? Yes, so use the signed result of -9.875.
    If IsUnsignedInput Then
        'If unsigned then we always expect a positive value so use straight conversion.
        Debug.Print("Result=" & resVal1)
    Else
        'If signed then we expect a positive OR negative value
        If resVal1 > decCeiling Then
            'Standard conversion yields a higher number than expected so use two's complement to get number
            Debug.Print("Result=" & resVal2)
        Else
            'Standard conversion yields a number that is in the expected range so use straight conversion to get number
            Debug.Print("Result=" & resVal1)
        End If
    End If

与传统系统进行背对背比较，所有这些都匹配，但是过去使用十六进制的工作量不大，我有点谨慎。对于此方法的任何进一步反馈，我将不胜感激。