private static TextPointer LetterShift_Exact(TextPointer start, int numLetters)
{
if (numLetters == 0 || start == null)
{
return(start);
}
int decrease = (numLetters < 0 ? -1 : 1);
TextPointer projectedEnd = start.GetPositionAtOffset(numLetters);
if (projectedEnd == null)
{
while (projectedEnd == null)
{
numLetters = numLetters - decrease;
projectedEnd = start.GetPositionAtOffset(numLetters);
if (numLetters == 0)
{
return(start);
}
}
return(projectedEnd);
}
int mover = (numLetters > 0 ? 1 : -1);
uint letterCount = (uint)Math.Abs(numLetters);
TextPointer ptrLastGood = projectedEnd;
while (start.GetLetterOffset(projectedEnd) < letterCount)
{
projectedEnd = projectedEnd.GetPositionAtOffset(mover);
if (projectedEnd == null)
{
return(ptrLastGood);
}
ptrLastGood = projectedEnd;
}
return(projectedEnd);
}
private static TextPointer LetterShift_Guess(TextPointer start, int numLetters, out int numOff)
{
if (numLetters == 0)
{
numOff = 0;
return(start);
}
TextPointer result = start.GetPositionAtOffset(numLetters);
if (result == null)
{
numOff = 0;
return(null);
}
if (!result.IsAtInsertionPosition)
{
TextPointer save;
if ((save = result.GetNextInsertionPosition(LogicalDirection.Backward)) == null)
{
if ((save = result.GetNextInsertionPosition(LogicalDirection.Forward)) == null)
{
numOff = 0;
return(null);
}
}
result = save;
}
bool wasNegative = numLetters < 0;
numOff = Math.Abs(numLetters) - start.GetLetterOffset(result);
if (wasNegative)
{
numOff *= -1;
}
return(result);
}