1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package fuzz
6
7// queue holds a growable sequence of inputs for fuzzing and minimization.
8//
9// For now, this is a simple ring buffer
10// (https://en.wikipedia.org/wiki/Circular_buffer).
11//
12// TODO(golang.org/issue/46224): use a prioritization algorithm based on input
13// size, previous duration, coverage, and any other metrics that seem useful.
14type queue struct {
15	// elems holds a ring buffer.
16	// The queue is empty when begin = end.
17	// The queue is full (until grow is called) when end = begin + N - 1 (mod N)
18	// where N = cap(elems).
19	elems     []any
20	head, len int
21}
22
23func (q *queue) cap() int {
24	return len(q.elems)
25}
26
27func (q *queue) grow() {
28	oldCap := q.cap()
29	newCap := oldCap * 2
30	if newCap == 0 {
31		newCap = 8
32	}
33	newElems := make([]any, newCap)
34	oldLen := q.len
35	for i := 0; i < oldLen; i++ {
36		newElems[i] = q.elems[(q.head+i)%oldCap]
37	}
38	q.elems = newElems
39	q.head = 0
40}
41
42func (q *queue) enqueue(e any) {
43	if q.len+1 > q.cap() {
44		q.grow()
45	}
46	i := (q.head + q.len) % q.cap()
47	q.elems[i] = e
48	q.len++
49}
50
51func (q *queue) dequeue() (any, bool) {
52	if q.len == 0 {
53		return nil, false
54	}
55	e := q.elems[q.head]
56	q.elems[q.head] = nil
57	q.head = (q.head + 1) % q.cap()
58	q.len--
59	return e, true
60}
61
62func (q *queue) peek() (any, bool) {
63	if q.len == 0 {
64		return nil, false
65	}
66	return q.elems[q.head], true
67}
68
69func (q *queue) clear() {
70	*q = queue{}
71}
72