private const int MaximumSectionCount = 128; // This is the maximum granularity for GetBestStartPoint
private static ListSearchConfiguration UpdateListSearchConfiguration(IList list)
{
ListSearchConfiguration configuration = default(ListSearchConfiguration);
if (list is Array)
{
configuration.LowerBound = ((Array)list).GetLowerBound(0);
configuration.UpperBound = ((Array)list).GetUpperBound(0);
}
else
{
configuration.LowerBound = 0;
configuration.UpperBound = list.Count - 1;
}
configuration.ListSize = list.Count;
configuration.SectionSize = InitialSectionSize;
while (configuration.SectionSize > 0 && (list.Count / configuration.SectionSize) > MaximumSectionCount)
{
configuration.SectionSize *= 2;
}
while (configuration.SectionSize > 0 && (list.Count / configuration.SectionSize) < 1)
{
configuration.SectionSize /= 2;
}
configuration.InitialCutSize = (configuration.SectionSize / 2);
configuration.SectionCount = configuration.SectionSize > 0 ? (list.Count / configuration.SectionSize) : 0;
return(configuration);
}
public static int[] FindIndexBinary <T>(this IList list, T item, IComparer <T> comparer = null)
{
if (comparer == null)
{
comparer = Comparer <T> .Default;
}
ListSearchConfiguration configuration = default(ListSearchConfiguration);
if (listSearchConfigCache.ContainsKey(list))
{
configuration = listSearchConfigCache[list];
}
if (configuration.ListSize == 0 || list.Count > configuration.SectionCount * configuration.SectionSize ||
Math.Abs(list.Count - configuration.ListSize) > configuration.SectionSize)
{
if (listSearchConfigCache.ContainsKey(list))
{
listSearchConfigCache[list] = UpdateListSearchConfiguration(list);
}
else
{
listSearchConfigCache.Add(list, configuration = UpdateListSearchConfiguration(list));
}
}
if (list.Count == 0 || comparer.Compare(item, (T)list[configuration.LowerBound]) == -1)
{
return(new[] { -1, 0 });
}
if (comparer.Compare(item, (T)list[configuration.UpperBound]) == 1)
{
return(new[] { configuration.UpperBound, configuration.UpperBound + 1 });
}
return(FindIndexBinaryCore(list, item, comparer, configuration));
}
private static int GetBestStartPoint <T>(IList list, T item, IComparer <T> comparer, ListSearchConfiguration configuration)
{
int startPoint = configuration.UpperBound - configuration.InitialCutSize;
for (int i = configuration.LowerBound; i <= configuration.UpperBound; i += configuration.SectionSize)
{
if (comparer.Compare(item, (T)list[i]) == -1)
{
startPoint = i - configuration.InitialCutSize;
break;
}
}
return(startPoint);
}
private static int[] FindIndexBinaryCore <T>(IList list, T item, IComparer <T> comparer, ListSearchConfiguration configuration)
{
int startPoint = GetBestStartPoint(list, item, comparer, configuration);
int[] result = { 0, startPoint };
int cutSize = configuration.InitialCutSize;
int nextCompareResult = comparer.Compare(item, (T)list[result[1]]);
while (true)
{
result[0] = result[1];
if (nextCompareResult == 0)
{
return(result);
}
if (cutSize > 1)
{
cutSize /= 2;
}
result[1] += cutSize * nextCompareResult;
int compareResult = nextCompareResult;
nextCompareResult = result[1] < configuration.LowerBound ? 1 : comparer.Compare(item, (T)list[result[1]]);
if (compareResult == 1 && nextCompareResult == -1 && result[1] - result[0] == 1)
{
return(result);
}
}
}
