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SplitMix.scala
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SplitMix.scala
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/*
* Copyright 2021 Arman Bilge
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package schrodinger.unsafe
import cats.Applicative
import cats.effect.kernel.Clock
import cats.syntax.all.*
import java.lang
final class SplitMix(private[unsafe] var seed: Long, val gamma: Long) extends Serializable
object SplitMix:
def fromTime[F[_]: Applicative: Clock]: F[SplitMix] =
(Clock[F].realTime.map(_.length), Clock[F].monotonic.map(_.length)).mapN {
(currentTimeMillis, nanoTime) =>
val s = mix64(currentTimeMillis) ^ mix64(nanoTime)
SplitMix(mix64(s), mixGamma(s + GoldenGamma))
}
given SplittableRng[SplitMix] with
extension (s: SplitMix)
def copy(): SplitMix = SplitMix(s.seed, s.gamma)
def nextInt(): Int =
s.seed += s.gamma
mix32(s.seed)
def nextLong(): Long =
s.seed += s.gamma
mix64(s.seed)
def nextGamma(): Long =
s.seed += s.gamma
mixGamma(s.seed)
def split(): SplitMix =
val seed = s.nextLong()
val gamma = s.nextGamma()
SplitMix(seed, gamma)
final val GoldenGamma = 0x9e3779b97f4a7c15L
private inline def mix64(_z: Long) =
var z = _z
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL
z ^ (z >>> 31)
private inline def mix32(_z: Long) =
var z = _z
z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L
(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32).toInt
private inline def mixGamma(_z: Long) =
var z = _z
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L
z = (z ^ (z >>> 33)) | 1L
val n = lang.Long.bitCount(z ^ (z >>> 1))
if n < 24 then z ^ 0xaaaaaaaaaaaaaaaaL
else z