40 lines
938 B
Go
40 lines
938 B
Go
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build !go1.13
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package poly1305
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// Generic fallbacks for the math/bits intrinsics, copied from
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// src/math/bits/bits.go. They were added in Go 1.12, but Add64 and Sum64 had
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// variable time fallbacks until Go 1.13.
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func bitsAdd64(x, y, carry uint64) (sum, carryOut uint64) {
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sum = x + y + carry
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carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
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return
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}
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func bitsSub64(x, y, borrow uint64) (diff, borrowOut uint64) {
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diff = x - y - borrow
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borrowOut = ((^x & y) | (^(x ^ y) & diff)) >> 63
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return
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}
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func bitsMul64(x, y uint64) (hi, lo uint64) {
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const mask32 = 1<<32 - 1
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x0 := x & mask32
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x1 := x >> 32
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y0 := y & mask32
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y1 := y >> 32
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w0 := x0 * y0
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t := x1*y0 + w0>>32
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w1 := t & mask32
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w2 := t >> 32
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w1 += x0 * y1
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hi = x1*y1 + w2 + w1>>32
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lo = x * y
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return
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}
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