Convert numbers within a range to numbers within another range [duplicate]

Question

Possible Duplicate:
Convert a number range to another range, maintaining ratio

So I have a function that returns values within 0 and 255 and I need to convert these values to something between -255 and 255 So 200 would be roughly 145, 150 would be roughly 45 and so on.. I have looked at Convert a number range to another range, maintaining ratio but the formulas there won't work. Any other formula I could use?

Answer 1

public static int ConvertRange(
    int originalStart, int originalEnd, // original range
    int newStart, int newEnd, // desired range
    int value) // value to convert
{
    double scale = (double)(newEnd - newStart) / (originalEnd - originalStart);
    return (int)(newStart + ((value - originalStart) * scale));
}

Answer 2

Try this:

int Adjust( int num )
{
    return num * 2 - 255;
}