internal static IEnumerable <T> NNP <T>(IEnumerable <T> source, int from, int to, int step)
{
if (from >= to)
{
yield break;
}
var buffer = new DynamicRotativeBuffer <T>();
from = -from;
to = -to;
int count;
using (var enumerator = source.GetEnumerator())
{
buffer.BufferUpToCount(enumerator, from);
count = buffer.length;
if (from == count)
{
count += buffer.RotateUntilEndWithCount(enumerator);
}
}
to = Math.Min(from, count) - to;
int head = buffer.head;
int i = 0;
while (i < to)
{
i += step;
yield return(buffer.items[head]);
head = (head + step) % buffer.length;
}
}
internal static IEnumerable <T> NNN <T>(IEnumerable <T> source, int from, int to, int step)
{
if (from <= to)
{
yield break;
}
from = -from;
step = -step;
to = -to;
var buffer = new DynamicRotativeBuffer <T>();
using (var enumerator = source.GetEnumerator())
{
buffer.BufferUpToCount(enumerator, to);
if (buffer.length == to)
{
buffer.RotateUntilEndWithCount(enumerator);
}
}
var length = buffer.length;
if (length < from)
{
yield break;
}
var head = buffer.head - from;
var count = (Math.Min(length - from, to - from - 1) + step) / step;
while (count-- > 0)
{
yield return(buffer.items[(head + length) % length]);
head -= step;
}
}
internal static IEnumerable <T> NPP <T>(IEnumerable <T> source, int from, int?to, int step)
{
from = -from;
var buffer = new DynamicRotativeBuffer <T>();
int count;
var offset = 0;
if (to.HasValue)
{
var toValue = to.Value;
if (from >= toValue)
{
using (var enumerator = source.GetEnumerator())
{
buffer.BufferUpToCount(enumerator, toValue);
if (buffer.length != toValue)
{
offset = 0;
count = buffer.length;
}
else
{
var toSkip = from - toValue;
if (toSkip != enumerator.Skip(toSkip))
{
offset = 0;
count = buffer.length;
}
else
{
offset = enumerator.Skip(toValue);
count = toValue - offset;
}
}
}
}
else
{
using (var enumerator = source.GetEnumerator())
{
buffer.BufferUpToCount(enumerator, from);
count = buffer.length;
if (count != from)
{
offset = 0;
}
else
{
var toSkip = toValue - from;
if (toSkip != buffer.RotateUpToCount(enumerator, toSkip))
{
offset = 0;
count = buffer.length;
}
else
{
offset = enumerator.Skip(from);
count = from - offset;
}
}
}
}
}
else
{
using (var enumerator = source.GetEnumerator())
{
buffer.BufferUpToCount(enumerator, from);
if (buffer.length == from)
{
buffer.RotateUntilEndWithCount(enumerator);
}
}
count = buffer.length;
}
if (count <= 0)
{
yield break;
}
count = (count + step - 1) / step;
buffer.head += offset;
while (count-- > 0)
{
yield return(buffer.items[buffer.head % buffer.length]);
buffer.head += step;
}
}