queue.go

// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

package sctp

type queue[T any] struct {
	buf   []T
	head  int
	tail  int
	count int
}

const minCap = 16

func newQueue[T any](capacity int) *queue[T] {
	queueCap := minCap
	for queueCap < capacity {
		queueCap <<= 1
	}

	return &queue[T]{
		buf: make([]T, queueCap),
	}
}

func (q *queue[T]) Len() int {
	return q.count
}

func (q *queue[T]) PushBack(ele T) {
	q.growIfFull()
	q.buf[q.tail] = ele
	q.tail = (q.tail + 1) % len(q.buf)
	q.count++
}

func (q *queue[T]) PopFront() T {
	ele := q.buf[q.head]
	var zeroVal T
	q.buf[q.head] = zeroVal
	q.head = (q.head + 1) % len(q.buf)
	q.count--
	return ele
}

func (q *queue[T]) Front() T {
	return q.buf[q.head]
}

func (q *queue[T]) Back() T {
	return q.buf[(q.tail-1+len(q.buf))%len(q.buf)]
}

func (q *queue[T]) At(i int) T {
	return q.buf[(q.head+i)%(len(q.buf))]
}

func (q *queue[T]) growIfFull() {
	if q.count < len(q.buf) {
		return
	}

	newBuf := make([]T, q.count<<1)
	if q.tail > q.head {
		copy(newBuf, q.buf[q.head:q.tail])
	} else {
		n := copy(newBuf, q.buf[q.head:])
		copy(newBuf[n:], q.buf[:q.tail])
	}

	q.head = 0
	q.tail = q.count
	q.buf = newBuf
}