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