Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

pkg/tcpip/seqnum/BUILD

@@ -0,0 +1,26 @@
+package(licenses = ["notice"])  # BSD
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("//tools/go_stateify:defs.bzl", "go_stateify")
+
+go_stateify(
+    name = "seqnum_state",
+    srcs = [
+        "seqnum.go",
+    ],
+    out = "seqnum_state.go",
+    package = "seqnum",
+)
+
+go_library(
+    name = "seqnum",
+    srcs = [
+        "seqnum.go",
+        "seqnum_state.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum",
+    visibility = [
+        "//visibility:public",
+    ],
+    deps = ["//pkg/state"],
+)

pkg/tcpip/seqnum/seqnum.go

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+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package seqnum defines the types and methods for TCP sequence numbers such
+// that they fit in 32-bit words and work properly when overflows occur.
+package seqnum
+
+// Value represents the value of a sequence number.
+type Value uint32
+
+// Size represents the size (length) of a sequence number window.
+type Size uint32
+
+// LessThan checks if v is before w, i.e., v < w.
+func (v Value) LessThan(w Value) bool {
+	return int32(v-w) < 0
+}
+
+// LessThanEq returns true if v==w or v is before i.e., v < w.
+func (v Value) LessThanEq(w Value) bool {
+	if v == w {
+		return true
+	}
+	return v.LessThan(w)
+}
+
+// InRange checks if v is in the range [a,b), i.e., a <= v < b.
+func (v Value) InRange(a, b Value) bool {
+	return v-a < b-a
+}
+
+// InWindow checks if v is in the window that starts at 'first' and spans 'size'
+// sequence numbers.
+func (v Value) InWindow(first Value, size Size) bool {
+	return v.InRange(first, first.Add(size))
+}
+
+// Overlap checks if the window [a,a+b) overlaps with the window [x, x+y).
+func Overlap(a Value, b Size, x Value, y Size) bool {
+	return a.LessThan(x.Add(y)) && x.LessThan(a.Add(b))
+}
+
+// Add calculates the sequence number following the [v, v+s) window.
+func (v Value) Add(s Size) Value {
+	return v + Value(s)
+}
+
+// Size calculates the size of the window defined by [v, w).
+func (v Value) Size(w Value) Size {
+	return Size(w - v)
+}
+
+// UpdateForward updates v such that it becomes v + s.
+func (v *Value) UpdateForward(s Size) {
+	*v += Value(s)
+}