lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

vendor/github.com/klauspost/crc32/crc32_amd64p32.go

@@ -0,0 +1,43 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !appengine,!gccgo
+
+package crc32
+
+// This file contains the code to call the SSE 4.2 version of the Castagnoli
+// CRC.
+
+// haveSSE42 is defined in crc32_amd64p32.s and uses CPUID to test for SSE 4.2
+// support.
+func haveSSE42() bool
+
+// castagnoliSSE42 is defined in crc32_amd64p32.s and uses the SSE4.2 CRC32
+// instruction.
+//go:noescape
+func castagnoliSSE42(crc uint32, p []byte) uint32
+
+var sse42 = haveSSE42()
+
+func archAvailableCastagnoli() bool {
+	return sse42
+}
+
+func archInitCastagnoli() {
+	if !sse42 {
+		panic("not available")
+	}
+	// No initialization necessary.
+}
+
+func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
+	if !sse42 {
+		panic("not available")
+	}
+	return castagnoliSSE42(crc, p)
+}
+
+func archAvailableIEEE() bool                    { return false }
+func archInitIEEE()                              { panic("not available") }
+func archUpdateIEEE(crc uint32, p []byte) uint32 { panic("not available") }