From 0d09d1df66bcdbdf34329ef0ce61bb347b69b1b9 Mon Sep 17 00:00:00 2001
From: Elichai Turkel <elichai.turkel@gmail.com>
Date: Sat, 6 Nov 2021 21:43:41 +0200
Subject: [PATCH] Add a xoShiRo256PlusPlus implementation

---
 domain/consensus/utils/pow/xoshiro.go      | 37 ++++++++++++++++++++++
 domain/consensus/utils/pow/xoshiro_test.go | 17 ++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 domain/consensus/utils/pow/xoshiro.go
 create mode 100644 domain/consensus/utils/pow/xoshiro_test.go

diff --git a/domain/consensus/utils/pow/xoshiro.go b/domain/consensus/utils/pow/xoshiro.go
new file mode 100644
index 000000000..7775d58a7
--- /dev/null
+++ b/domain/consensus/utils/pow/xoshiro.go
@@ -0,0 +1,37 @@
+package pow
+
+import (
+	"encoding/binary"
+	"github.com/kaspanet/kaspad/domain/consensus/model/externalapi"
+	"math/bits"
+)
+
+type xoShiRo256PlusPlus struct {
+	s0 uint64
+	s1 uint64
+	s2 uint64
+	s3 uint64
+}
+
+func newxoShiRo256PlusPlus(hash *externalapi.DomainHash) *xoShiRo256PlusPlus {
+	hashArray := hash.ByteArray()
+	return &xoShiRo256PlusPlus{
+		s0: binary.LittleEndian.Uint64(hashArray[:8]),
+		s1: binary.LittleEndian.Uint64(hashArray[8:16]),
+		s2: binary.LittleEndian.Uint64(hashArray[16:24]),
+		s3: binary.LittleEndian.Uint64(hashArray[24:32]),
+	}
+}
+
+func (x *xoShiRo256PlusPlus) Uint64() uint64 {
+	res := bits.RotateLeft64(x.s0+x.s3, 23) + x.s0
+	t := x.s1 << 17
+	x.s2 ^= x.s0
+	x.s3 ^= x.s1
+	x.s1 ^= x.s2
+	x.s0 ^= x.s3
+
+	x.s2 ^= t
+	x.s3 = bits.RotateLeft64(x.s3, 45)
+	return res
+}
diff --git a/domain/consensus/utils/pow/xoshiro_test.go b/domain/consensus/utils/pow/xoshiro_test.go
new file mode 100644
index 000000000..6f9815984
--- /dev/null
+++ b/domain/consensus/utils/pow/xoshiro_test.go
@@ -0,0 +1,17 @@
+package pow
+
+import "testing"
+
+// Test vectors are from here: https://github.com/rust-random/rngs/blob/17aa826cc38d3e8408c9489ac859fa9397acd479/rand_xoshiro/src/xoshiro256plusplus.rs#L121
+func TestXoShiRo256PlusPlus_Uint64(t *testing.T) {
+	state := xoShiRo256PlusPlus{1, 2, 3, 4}
+	expected := []uint64{41943041, 58720359, 3588806011781223, 3591011842654386,
+		9228616714210784205, 9973669472204895162, 14011001112246962877,
+		12406186145184390807, 15849039046786891736, 10450023813501588000}
+	for _, ex := range expected {
+		val := state.Uint64()
+		if val != ex {
+			t.Errorf("expected: %d, found: %d", ex, val)
+		}
+	}
+}