class DataField(object):
    def __init__(self, name, offset):
        self.name = name
        self.offset = offset
    def value(self,data):
        raise NotImplemented()

 class Data1b(DataField):
     """
    Beispiel für die Berechnung:
    if ((x & 80h) == 80h) // y negativ
    y     = - [dez(!x) + 1]
    else 
    y     = dez(x)
    """
     def value(self,data):
         x = ord(data[self.offset])
         if x & 0x80 == 0x80:
             return (-1) * (0xff^x + 1)
         else:
             return x

class Data1c(DataField):
    def value(self,data):
        return ord(data[self.offset])/2.0
                 
class Data2c(DataField):
    """
    Beispiel für die Berechnung:
    if ((x & 8000h) == 8000h) // y negativ
    y = - [dez(High_Byte(!x)) 16 + dez(High_Nibble (Low_Byte (!x)))
    + (dez(Low_Nibble (Low_Byte (!x))) +1 ) / 16]
    else                       // y positiv
    y = dez(High_Byte(x)) 16 + dez(High_ Nibble (Low Byte (x)))
    + dez(Low_ Nibble (Low Byte (x))) / 16
    """
    def value(self,data):
        highByte = ord(data[self.offset+1])
        lowByte= ord(data[self.offset])
        if (0x8000 & (highByte<<8 | lowByte)) == 0x8000:
            return (-1) * ( (0xff^highByte)*16 + (0xff^(lowByte>>4)) + (0x0ff^(0xf&lowByte) + 1)/16.0 )
        else:
            return highByte*16 + (lowByte>>4) + (lowByte&0xf)/16.0

class Data2b(DataField):
    """
    if ((x&8000h) == 8000h) // y negativ
    y = - [dez(High_Byte(!x)) + (dez(Low_Byte(!x)) + 1) / 256]
    else                        // y positiv
    y = dez(High_Byte (x)) + dez(Low_Byte (x)) / 256
    """
    def value(self,data):
        highByte = ord(data[self.offset+1])
        lowByte= ord(data[self.offset])
        if (0x8000 & (highByte<<8 | lowByte)) == 0x8000:
            return (-1) * ((0xff^highByte) + (0xff^lowByte+1)/256.0)
        else:
            return highByte + lowByte/256.0
        
class Bit(DataField):
    def value(self, data):
        return ord(data[self.offset]) == 0x1
    
class Word(DataField):
    def value(self, data):
        lb, hb = data[self.offset], data[self.offset+1]
        return ord(lb) + (ord(hb)<<8)
    
class Bcd(DataField):
    """
    y = dez(High_Nibble(x))*10 + dez(Low_Nibble(x))
    """
    def value(self, data):
        byte = ord(data[self.offset])
        return (byte >> 4) * 10 + (byte & 0xf)
    
class Byte(DataField):
    def value(self, data):
        return ord(data[self.offset])
    

class ByteEnum(DataField):
    def __init__(self, name, offset, values):
        fields.DataField.__init__(self, name, offset)
        self.values = values

    def value(self, data):
        value = ord(data[self.offset])
        if self.values.has_key(value):
            return self.values[value]
        else:
            return None