HexPosition?FindCoreReverse(SearchState state, HexPosition start, HexPosition lowerBounds)
{
var patternLocal = pattern;
var maskLocal = mask;
var pos = start;
state.SetPreviousPosition(pos);
var patternLocal0 = patternLocal[patternLocal.Length - 1];
var maskLocal0 = maskLocal[maskLocal.Length - 1];
var patternLocal1 = patternLocal.Length <= 1 ? 0 : patternLocal[patternLocal.Length - 2];
var maskLocal1 = maskLocal.Length <= 1 ? 0 : maskLocal[maskLocal.Length - 2];
var maskLocalLengthIsAtLeast2 = maskLocal.Length >= 2;
loop:
// This loop doesn't check the cancellation token because SearchState does that
// every time it reads new memory from the buffer.
if (pos < lowerBounds)
{
return(null);
}
int skip;
HexPosition?beforePos;
if (maskLocalLengthIsAtLeast2)
{
skip = 2;
beforePos = maskLocal0 == 0xFF ?
state.PositionBefore2(patternLocal0, patternLocal1, maskLocal1, lowerBounds) :
state.PositionBeforeWithMask2(patternLocal0, patternLocal1, maskLocal0, maskLocal1, lowerBounds);
}
else if (maskLocal0 == 0xFF)
{
skip = 1;
beforePos = state.PositionBefore1(patternLocal0, lowerBounds);
}
else
{
skip = 1;
beforePos = state.PositionBeforeWithMask1(patternLocal0, maskLocal0, lowerBounds);
}
if (beforePos == null)
{
return(null);
}
pos = beforePos.Value;
for (int i = patternLocal.Length - 1 - skip; i >= 0; i--)
{
var b = state.GetPreviousByte();
var m = maskLocal[i];
if ((b & m) != patternLocal[i])
{
pos = pos + (skip - 1);
state.SetPreviousPosition(pos);
goto loop;
}
}
return(pos - (patternLocal.LongLength - skip - 1));
}