1// Copyright 2019 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// +build !go1.13
6
7package poly1305
8
9// Generic fallbacks for the math/bits intrinsics, copied from
10// src/math/bits/bits.go. They were added in Go 1.12, but Add64 and Sum64 had
11// variable time fallbacks until Go 1.13.
12
13func bitsAdd64(x, y, carry uint64) (sum, carryOut uint64) {
14	sum = x + y + carry
15	carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
16	return
17}
18
19func bitsSub64(x, y, borrow uint64) (diff, borrowOut uint64) {
20	diff = x - y - borrow
21	borrowOut = ((^x & y) | (^(x ^ y) & diff)) >> 63
22	return
23}
24
25func bitsMul64(x, y uint64) (hi, lo uint64) {
26	const mask32 = 1<<32 - 1
27	x0 := x & mask32
28	x1 := x >> 32
29	y0 := y & mask32
30	y1 := y >> 32
31	w0 := x0 * y0
32	t := x1*y0 + w0>>32
33	w1 := t & mask32
34	w2 := t >> 32
35	w1 += x0 * y1
36	hi = x1*y1 + w2 + w1>>32
37	lo = x * y
38	return
39}
40