39 lines
1.0 KiB
Go
39 lines
1.0 KiB
Go
|
// Copied from https://cs.opensource.google/go/go/+/946b4baaf6521d521928500b2b57429c149854e7:src/math/bits.go
|
||
|
|
|
||
|
|
// Copyright 2017 The Go Authors. All rights reserved.
|
||
|
|
// Use of this source code is governed by a BSD-style
|
||
|
|
// license that can be found in the LICENSE file.
|
||
|
|
|
||
|
|
package rand
|
||
|
|
|
||
|
|
// Add64 returns the sum with carry of x, y and carry: sum = x + y + carry.
|
||
|
|
// The carry input must be 0 or 1; otherwise the behavior is undefined.
|
||
|
|
// The carryOut output is guaranteed to be 0 or 1.
|
||
|
|
func Add64(x, y, carry uint64) (sum, carryOut uint64) {
|
||
|
|
yc := y + carry
|
||
|
|
sum = x + yc
|
||
|
|
if sum < x || yc < y {
|
||
|
|
carryOut = 1
|
||
|
|
}
|
||
|
|
return
|
||
|
|
}
|
||
|
|
|
||
|
|
// Mul64 returns the 128-bit product of x and y: (hi, lo) = x * y
|
||
|
|
// with the product bits' upper half returned in hi and the lower
|
||
|
|
// half returned in lo.
|
||
|
|
func Mul64(x, y uint64) (hi, lo uint64) {
|
||
|
|
const mask32 = 1<<32 - 1
|
||
|
|
x0 := x & mask32
|
||
|
|
x1 := x >> 32
|
||
|
|
y0 := y & mask32
|
||
|
|
y1 := y >> 32
|
||
|
|
w0 := x0 * y0
|
||
|
|
t := x1*y0 + w0>>32
|
||
|
|
w1 := t & mask32
|
||
|
|
w2 := t >> 32
|
||
|
|
w1 += x0 * y1
|
||
|
|
hi = x1*y1 + w2 + w1>>32
|
||
|
|
lo = x * y
|
||
|
|
return
|
||
|
|
}
|