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using System;
namespace ARMeilleure.CodeGen.RegisterAllocators
{
unsafe struct UseList
{
private int* _items;
private int _capacity;
public int Count { get; private set; }
public readonly int FirstUse => Count > 0 ? _items[Count - 1] : LiveInterval.NotFound;
public readonly Span<int> Span => new(_items, Count);
public void Add(int position)
{
if (Count + 1 > _capacity)
{
var oldSpan = Span;
_capacity = Math.Max(4, _capacity * 2);
_items = Allocators.Default.Allocate<int>((uint)_capacity);
var newSpan = Span;
oldSpan.CopyTo(newSpan);
}
// Use positions are usually inserted in descending order, so inserting in descending order is faster,
// since the number of half exchanges is reduced.
int i = Count - 1;
while (i >= 0 && _items[i] < position)
{
_items[i + 1] = _items[i--];
}
_items[i + 1] = position;
Count++;
}
public readonly int NextUse(int position)
{
int index = NextUseIndex(position);
return index != LiveInterval.NotFound ? _items[index] : LiveInterval.NotFound;
}
public readonly int NextUseIndex(int position)
{
int i = Count - 1;
if (i == -1 || position > _items[0])
{
return LiveInterval.NotFound;
}
while (i >= 0 && _items[i] < position)
{
i--;
}
return i;
}
public UseList Split(int position)
{
int index = NextUseIndex(position);
// Since the list is in descending order, the new split list takes the front of the list and the current
// list takes the back of the list.
UseList result = new()
{
Count = index + 1,
};
result._capacity = result.Count;
result._items = _items;
Count -= result.Count;
_capacity = Count;
_items += result.Count;
return result;
}
}
}
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