1 // Copyright 2018 The gVisor Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 15 // Package seqnum defines the types and methods for TCP sequence numbers such
16 // that they fit in 32-bit words and work properly when overflows occur.
17 package seqnum
18 19 // Value represents the value of a sequence number.
20 type Value uint32
21 22 // Size represents the size (length) of a sequence number window.
23 type Size uint32
24 25 // LessThan checks if v is before w, i.e., v < w.
26 func (v Value) LessThan(w Value) bool {
27 return int32(v-w) < 0
28 }
29 30 // LessThanEq returns true if v==w or v is before i.e., v < w.
31 func (v Value) LessThanEq(w Value) bool {
32 if v == w {
33 return true
34 }
35 return v.LessThan(w)
36 }
37 38 // InRange checks if v is in the range [a,b), i.e., a <= v < b.
39 func (v Value) InRange(a, b Value) bool {
40 return v-a < b-a
41 }
42 43 // InWindow checks if v is in the window that starts at 'first' and spans 'size'
44 // sequence numbers.
45 func (v Value) InWindow(first Value, size Size) bool {
46 return v.InRange(first, first.Add(size))
47 }
48 49 // Add calculates the sequence number following the [v, v+s) window.
50 func (v Value) Add(s Size) Value {
51 return v + Value(s)
52 }
53 54 // Size calculates the size of the window defined by [v, w).
55 func (v Value) Size(w Value) Size {
56 return Size(w - v)
57 }
58 59 // UpdateForward updates v such that it becomes v + s.
60 func (v *Value) UpdateForward(s Size) {
61 *v += Value(s)
62 }
63