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f9eb3e3cd5
Cleanup and friction reduction. Updates #65355. Change-Id: I6c4fcd409d044c00d16561fe9ed2257877d73f5b Reviewed-on: https://go-review.googlesource.com/c/go/+/600435 Reviewed-by: Keith Randall <khr@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@golang.org>
56 lines
1.7 KiB
Go
56 lines
1.7 KiB
Go
// Copyright 2018 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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package math
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import "internal/goarch"
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const MaxUintptr = ^uintptr(0)
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// MulUintptr returns a * b and whether the multiplication overflowed.
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// On supported platforms this is an intrinsic lowered by the compiler.
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func MulUintptr(a, b uintptr) (uintptr, bool) {
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if a|b < 1<<(4*goarch.PtrSize) || a == 0 {
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return a * b, false
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}
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overflow := b > MaxUintptr/a
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return a * b, overflow
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}
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// Mul64 returns the 128-bit product of x and y: (hi, lo) = x * y
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// with the product bits' upper half returned in hi and the lower
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// half returned in lo.
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// This is a copy from math/bits.Mul64
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// On supported platforms this is an intrinsic lowered by the compiler.
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func Mul64(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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// Add64 returns the sum with carry of x, y and carry: sum = x + y + carry.
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// The carry input must be 0 or 1; otherwise the behavior is undefined.
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// The carryOut output is guaranteed to be 0 or 1.
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//
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// This function's execution time does not depend on the inputs.
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// On supported platforms this is an intrinsic lowered by the compiler.
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func Add64(x, y, carry uint64) (sum, carryOut uint64) {
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sum = x + y + carry
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// The sum will overflow if both top bits are set (x & y) or if one of them
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// is (x | y), and a carry from the lower place happened. If such a carry
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// happens, the top bit will be 1 + 0 + 1 = 0 (&^ sum).
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carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
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return
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}
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