add day-22 + benchmarks

day-22/internal/randomiser/randomiser.go

@@ -0,0 +1,43 @@
+package randomiser
+
+type Randomiser struct {
+	secret int
+}
+
+func New(secret int) *Randomiser {
+	return &Randomiser{secret: secret}
+}
+
+func (r *Randomiser) multiplyBy(n int) int {
+	return r.secret * n
+}
+
+func (r *Randomiser) divideBy(n int) int {
+	return r.secret / n
+}
+
+func (r *Randomiser) mix(a int) {
+	r.secret ^= a
+}
+
+func (r *Randomiser) prune() {
+	r.secret %= 16777216
+}
+
+func (r *Randomiser) Randomise() {
+	res := r.multiplyBy(64)
+	r.mix(res)
+	r.prune()
+
+	res = r.divideBy(32)
+	r.mix(res)
+	r.prune()
+
+	res = r.multiplyBy(2048)
+	r.mix(res)
+	r.prune()
+}
+
+func (r *Randomiser) Secret() int {
+	return r.secret
+}

day-22/internal/randomiser/randomiser_internal_test.go

@@ -0,0 +1,19 @@
+package randomiser
+
+import "testing"
+
+func TestRandomiserMix(t *testing.T) {
+	r := New(42)
+	r.mix(15)
+	if r.secret != 37 {
+		t.Errorf("r.secret: got = %d want = 3", r.secret)
+	}
+}
+
+func TestRandomiserPrune(t *testing.T) {
+	r := New(10e7)
+	r.prune()
+	if r.secret != 16113920 {
+		t.Errorf("r.secret: got = %d want = 16113920", r.secret)
+	}
+}