1// Copyright 2018 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
 5//go:build gc && !purego
 6
 7package poly1305
 8
 9import (
10	"golang.org/x/sys/cpu"
11)
12
13// updateVX is an assembly implementation of Poly1305 that uses vector
14// instructions. It must only be called if the vector facility (vx) is
15// available.
16//
17//go:noescape
18func updateVX(state *macState, msg []byte)
19
20// mac is a replacement for macGeneric that uses a larger buffer and redirects
21// calls that would have gone to updateGeneric to updateVX if the vector
22// facility is installed.
23//
24// A larger buffer is required for good performance because the vector
25// implementation has a higher fixed cost per call than the generic
26// implementation.
27type mac struct {
28	macState
29
30	buffer [16 * TagSize]byte // size must be a multiple of block size (16)
31	offset int
32}
33
34func (h *mac) Write(p []byte) (int, error) {
35	nn := len(p)
36	if h.offset > 0 {
37		n := copy(h.buffer[h.offset:], p)
38		if h.offset+n < len(h.buffer) {
39			h.offset += n
40			return nn, nil
41		}
42		p = p[n:]
43		h.offset = 0
44		if cpu.S390X.HasVX {
45			updateVX(&h.macState, h.buffer[:])
46		} else {
47			updateGeneric(&h.macState, h.buffer[:])
48		}
49	}
50
51	tail := len(p) % len(h.buffer) // number of bytes to copy into buffer
52	body := len(p) - tail          // number of bytes to process now
53	if body > 0 {
54		if cpu.S390X.HasVX {
55			updateVX(&h.macState, p[:body])
56		} else {
57			updateGeneric(&h.macState, p[:body])
58		}
59	}
60	h.offset = copy(h.buffer[:], p[body:]) // copy tail bytes - can be 0
61	return nn, nil
62}
63
64func (h *mac) Sum(out *[TagSize]byte) {
65	state := h.macState
66	remainder := h.buffer[:h.offset]
67
68	// Use the generic implementation if we have 2 or fewer blocks left
69	// to sum. The vector implementation has a higher startup time.
70	if cpu.S390X.HasVX && len(remainder) > 2*TagSize {
71		updateVX(&state, remainder)
72	} else if len(remainder) > 0 {
73		updateGeneric(&state, remainder)
74	}
75	finalize(out, &state.h, &state.s)
76}