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
5package math
6
7import "internal/goarch"
8
9const MaxUintptr = ^uintptr(0)
10
11// MulUintptr returns a * b and whether the multiplication overflowed.
12// On supported platforms this is an intrinsic lowered by the compiler.
13func MulUintptr(a, b uintptr) (uintptr, bool) {
14	if a|b < 1<<(4*goarch.PtrSize) || a == 0 {
15		return a * b, false
16	}
17	overflow := b > MaxUintptr/a
18	return a * b, overflow
19}
20
21// Mul64 returns the 128-bit product of x and y: (hi, lo) = x * y
22// with the product bits' upper half returned in hi and the lower
23// half returned in lo.
24// This is a copy from math/bits.Mul64
25// On supported platforms this is an intrinsic lowered by the compiler.
26func Mul64(x, y uint64) (hi, lo uint64) {
27	const mask32 = 1<<32 - 1
28	x0 := x & mask32
29	x1 := x >> 32
30	y0 := y & mask32
31	y1 := y >> 32
32	w0 := x0 * y0
33	t := x1*y0 + w0>>32
34	w1 := t & mask32
35	w2 := t >> 32
36	w1 += x0 * y1
37	hi = x1*y1 + w2 + w1>>32
38	lo = x * y
39	return
40}
41
42// Add64 returns the sum with carry of x, y and carry: sum = x + y + carry.
43// The carry input must be 0 or 1; otherwise the behavior is undefined.
44// The carryOut output is guaranteed to be 0 or 1.
45//
46// This function's execution time does not depend on the inputs.
47// On supported platforms this is an intrinsic lowered by the compiler.
48func Add64(x, y, carry uint64) (sum, carryOut uint64) {
49	sum = x + y + carry
50	// The sum will overflow if both top bits are set (x & y) or if one of them
51	// is (x | y), and a carry from the lower place happened. If such a carry
52	// happens, the top bit will be 1 + 0 + 1 = 0 (&^ sum).
53	carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
54	return
55}
56