use math/rand/v2 for randomness

game/game.go

@@ -11,6 +11,7 @@ package game
 
 import (
 	"errors"
+	"math/rand/v2"
 	"time"
 
 	"git.sunturtle.xyz/studio/shotgun/player"
@@ -18,8 +19,6 @@ import (
 )
 
 type Match struct {
-	// rng is the PRNG state used for this match.
-	rng xoshiro
 	// players are the players in the match. The first element is the dealer
 	// and the second is the challenger.
 	players [2]playerState
@@ -50,7 +49,6 @@ type Match struct {
 // New creates a new match started at round 1.
 func New(dealer, challenger player.ID) *Match {
 	g := &Match{
-		rng: newRNG(),
 		players: [2]playerState{
 			{id: dealer},
 			{id: challenger},
@@ -62,7 +60,7 @@ func New(dealer, challenger player.ID) *Match {
 
 // NextRound starts the next round of a match.
 func (g *Match) NextRound() {
-	g.hp = int8(g.rng.Intn(3) + 2)
+	g.hp = int8(rand.IntN(3) + 2)
 	g.players[0].startRound(g.hp)
 	g.players[1].startRound(g.hp)
 	g.round++
@@ -71,10 +69,10 @@ func (g *Match) NextRound() {
 
 // NextGame starts the next game of a round.
 func (g *Match) NextGame() {
-	items := g.rng.Intn(4) + 1
-	g.players[0].startGame(&g.rng, items)
-	g.players[1].startGame(&g.rng, items)
-	shells := g.rng.Intn(6) + 2
+	items := rand.IntN(4) + 1
+	g.players[0].startGame(items)
+	g.players[1].startGame(items)
+	shells := rand.IntN(6) + 2
 	for i := 0; i < shells/2; i++ {
 		g.shellArray[i] = true
 	}
@@ -82,7 +80,7 @@ func (g *Match) NextGame() {
 		g.shellArray[i] = false
 	}
 	g.shells = g.shellArray[:shells]
-	shuffle(&g.rng, g.shells)
+	shuffle(g.shells)
 	g.turn = 0
 	g.prev = nil
 	g.nextTurn()

game/item.go

@@ -1,5 +1,7 @@
 package game
 
+import "math/rand/v2"
+
 type item int8
 
 const (
@@ -11,8 +13,8 @@ const (
 	itemKnife
 )
 
-func newItem(rng *xoshiro) item {
-	return item(rng.Intn(5)) + 1
+func newItem() item {
+	return item(rand.IntN(5)) + 1
 }
 
 func (i item) apply(g *Match) bool {

game/player.go

@@ -19,13 +19,13 @@ func (p *playerState) startRound(hp int8) {
 	clear(p.items[:])
 }
 
-func (p *playerState) startGame(rng *xoshiro, items int) {
+func (p *playerState) startGame(items int) {
 	for i := 0; i < items; i++ {
 		k := slices.Index(p.items[:], itemNone)
 		if k < 0 {
 			break
 		}
-		p.items[k] = newItem(rng)
+		p.items[k] = newItem()
 	}
 	p.cuffs = uncuffed
 }

game/rng.go

@@ -1,65 +1,10 @@
 package game
 
-import (
-	"crypto/rand"
-	"encoding/binary"
-	"math/bits"
-)
+import "math/rand/v2"
 
-// xoshiro is a random number generator for shotgun.
-//
-// Currently xoshiro256**. Subject to change.
-type xoshiro struct {
-	w, x, y, z uint64
-}
-
-// newRNG produces a new, uniquely seeded RNG.
-func newRNG() xoshiro {
-	r := xoshiro{}
-	b := make([]byte, 8*4)
-	// Loop to ensure the state is never all-zero, which is an invalid state
-	// for xoshiro.
-	for r.w == 0 && r.x == 0 && r.y == 0 && r.z == 0 {
-		rand.Read(b)
-		r.w = binary.LittleEndian.Uint64(b)
-		r.x = binary.LittleEndian.Uint64(b[8:])
-		r.y = binary.LittleEndian.Uint64(b[16:])
-		r.z = binary.LittleEndian.Uint64(b[24:])
-	}
-	return r
-}
-
-// Uint64 produces a 64-bit pseudo-random value.
-func (rng *xoshiro) Uint64() uint64 {
-	w, x, y, z := rng.w, rng.x, rng.y, rng.z
-	r := bits.RotateLeft64(x*5, 7) * 9
-	t := x << 17
-	y ^= w
-	z ^= x
-	x ^= y
-	w ^= z
-	y ^= t
-	z = bits.RotateLeft64(z, 45)
-	rng.w, rng.x, rng.y, rng.z = w, x, y, z
-	return r
-}
-
-// Intn produces an int in [0, n). Panics if n <= 0.
-func (rng *xoshiro) Intn(n int) int {
-	if n <= 0 {
-		panic("shotgun: rng.Intn max below zero")
-	}
-	bad := ^uint(0) - ^uint(0)%uint(n)
-	x := uint(rng.Uint64())
-	for x > bad {
-		x = uint(rng.Uint64())
-	}
-	return int(x % uint(n))
-}
-
-func shuffle[E any, S ~[]E](rng *xoshiro, s S) {
+func shuffle[E any, S ~[]E](s S) {
 	for i := len(s) - 1; i > 0; i-- {
-		j := rng.Intn(i + 1)
+		j := rand.IntN(i + 1)
 		s[i], s[j] = s[j], s[i]
 	}
 }