rand/uint64_fallback.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.

// +build !go1.9

package rand

// Uint64 returns a pseudo-random 64-bit unsigned integer as a uint64.
func (pcg *PCGSource) Uint64() uint64 {
	pcg.multiply()
	pcg.add()
	// XOR high and low 64 bits together and rotate right by high 6 bits of state.
	return rotateLeft(pcg.high^pcg.low, -int(pcg.high>>58))
}

func rotateLeft(x uint64, k int) uint64 {
	const n = 64
	s := uint(k) & (n - 1)
	return x<<s | x>>(n-s)
}