1 files changed, 50 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/modulo_test.go b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/modulo_test.go
new file mode 100644
index 0000000..da963c7
--- /dev/null
+++ b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/modulo_test.go
@@ -0,0 +1,50 @@
+// 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.
+
+// This file validates that the calculation in Uint64n corrects for
+// possible bias.
+
+package rand
+
+import (
+	"testing"
+)
+
+// modSource is used to probe the upper region of uint64 space. It
+// generates values sequentially in [maxUint64-15,maxUint64]. With
+// modEdge == 15 and maxUint64 == 1<<64-1 == 18446744073709551615,
+// this means that Uint64n(10) will repeatedly probe the top range.
+// We thus expect a bias to result unless the calculation in Uint64n
+// gets the edge condition right. We test this by calling Uint64n 100
+// times; the results should be perfectly evenly distributed across
+// [0,10).
+type modSource uint64
+
+const modEdge = 15
+
+func (m *modSource) Seed(uint64) {}
+
+// Uint64 returns a non-pseudo-random 64-bit unsigned integer as a uint64.
+func (m *modSource) Uint64() uint64 {
+	if *m > modEdge {
+		*m = 0
+	}
+	r := maxUint64 - *m
+	*m++
+	return uint64(r)
+}
+
+func TestUint64Modulo(t *testing.T) {
+	var src modSource
+	rng := New(&src)
+	var result [10]uint64
+	for i := 0; i < 100; i++ {
+		result[rng.Uint64n(10)]++
+	}
+	for _, r := range result {
+		if r != 10 {
+			t.Fatal(result)
+		}
+	}
+}