1 files changed, 173 insertions, 0 deletions
diff --git a/pkg/buffer/buffer_list.go b/pkg/buffer/buffer_list.go
new file mode 100755
index 000000000..f3c27c42c
--- /dev/null
+++ b/pkg/buffer/buffer_list.go
@@ -0,0 +1,173 @@
+package buffer
+
+// ElementMapper provides an identity mapping by default.
+//
+// This can be replaced to provide a struct that maps elements to linker
+// objects, if they are not the same. An ElementMapper is not typically
+// required if: Linker is left as is, Element is left as is, or Linker and
+// Element are the same type.
+type bufferElementMapper struct{}
+
+// linkerFor maps an Element to a Linker.
+//
+// This default implementation should be inlined.
+//
+//go:nosplit
+func (bufferElementMapper) linkerFor(elem *Buffer) *Buffer { return elem }
+
+// List is an intrusive list. Entries can be added to or removed from the list
+// in O(1) time and with no additional memory allocations.
+//
+// The zero value for List is an empty list ready to use.
+//
+// To iterate over a list (where l is a List):
+//      for e := l.Front(); e != nil; e = e.Next() {
+// 		// do something with e.
+//      }
+//
+// +stateify savable
+type bufferList struct {
+	head *Buffer
+	tail *Buffer
+}
+
+// Reset resets list l to the empty state.
+func (l *bufferList) Reset() {
+	l.head = nil
+	l.tail = nil
+}
+
+// Empty returns true iff the list is empty.
+func (l *bufferList) Empty() bool {
+	return l.head == nil
+}
+
+// Front returns the first element of list l or nil.
+func (l *bufferList) Front() *Buffer {
+	return l.head
+}
+
+// Back returns the last element of list l or nil.
+func (l *bufferList) Back() *Buffer {
+	return l.tail
+}
+
+// PushFront inserts the element e at the front of list l.
+func (l *bufferList) PushFront(e *Buffer) {
+	bufferElementMapper{}.linkerFor(e).SetNext(l.head)
+	bufferElementMapper{}.linkerFor(e).SetPrev(nil)
+
+	if l.head != nil {
+		bufferElementMapper{}.linkerFor(l.head).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+
+	l.head = e
+}
+
+// PushBack inserts the element e at the back of list l.
+func (l *bufferList) PushBack(e *Buffer) {
+	bufferElementMapper{}.linkerFor(e).SetNext(nil)
+	bufferElementMapper{}.linkerFor(e).SetPrev(l.tail)
+
+	if l.tail != nil {
+		bufferElementMapper{}.linkerFor(l.tail).SetNext(e)
+	} else {
+		l.head = e
+	}
+
+	l.tail = e
+}
+
+// PushBackList inserts list m at the end of list l, emptying m.
+func (l *bufferList) PushBackList(m *bufferList) {
+	if l.head == nil {
+		l.head = m.head
+		l.tail = m.tail
+	} else if m.head != nil {
+		bufferElementMapper{}.linkerFor(l.tail).SetNext(m.head)
+		bufferElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
+
+		l.tail = m.tail
+	}
+
+	m.head = nil
+	m.tail = nil
+}
+
+// InsertAfter inserts e after b.
+func (l *bufferList) InsertAfter(b, e *Buffer) {
+	a := bufferElementMapper{}.linkerFor(b).Next()
+	bufferElementMapper{}.linkerFor(e).SetNext(a)
+	bufferElementMapper{}.linkerFor(e).SetPrev(b)
+	bufferElementMapper{}.linkerFor(b).SetNext(e)
+
+	if a != nil {
+		bufferElementMapper{}.linkerFor(a).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+}
+
+// InsertBefore inserts e before a.
+func (l *bufferList) InsertBefore(a, e *Buffer) {
+	b := bufferElementMapper{}.linkerFor(a).Prev()
+	bufferElementMapper{}.linkerFor(e).SetNext(a)
+	bufferElementMapper{}.linkerFor(e).SetPrev(b)
+	bufferElementMapper{}.linkerFor(a).SetPrev(e)
+
+	if b != nil {
+		bufferElementMapper{}.linkerFor(b).SetNext(e)
+	} else {
+		l.head = e
+	}
+}
+
+// Remove removes e from l.
+func (l *bufferList) Remove(e *Buffer) {
+	prev := bufferElementMapper{}.linkerFor(e).Prev()
+	next := bufferElementMapper{}.linkerFor(e).Next()
+
+	if prev != nil {
+		bufferElementMapper{}.linkerFor(prev).SetNext(next)
+	} else {
+		l.head = next
+	}
+
+	if next != nil {
+		bufferElementMapper{}.linkerFor(next).SetPrev(prev)
+	} else {
+		l.tail = prev
+	}
+}
+
+// Entry is a default implementation of Linker. Users can add anonymous fields
+// of this type to their structs to make them automatically implement the
+// methods needed by List.
+//
+// +stateify savable
+type bufferEntry struct {
+	next *Buffer
+	prev *Buffer
+}
+
+// Next returns the entry that follows e in the list.
+func (e *bufferEntry) Next() *Buffer {
+	return e.next
+}
+
+// Prev returns the entry that precedes e in the list.
+func (e *bufferEntry) Prev() *Buffer {
+	return e.prev
+}
+
+// SetNext assigns 'entry' as the entry that follows e in the list.
+func (e *bufferEntry) SetNext(elem *Buffer) {
+	e.next = elem
+}
+
+// SetPrev assigns 'entry' as the entry that precedes e in the list.
+func (e *bufferEntry) SetPrev(elem *Buffer) {
+	e.prev = elem
+}