From 51bddd4a0ff00fce883583852a2d225d5b41117c Mon Sep 17 00:00:00 2001
From: ekrctb <ekrctb@gmail.com>
Date: Mon, 30 Nov 2020 18:46:28 +0900
Subject: [PATCH] Rename functions, and add NextInt.

---
 osu.Game/Utils/StatelessRNG.cs | 42 +++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/osu.Game/Utils/StatelessRNG.cs b/osu.Game/Utils/StatelessRNG.cs
index d78d55cc09..d316f718e3 100644
--- a/osu.Game/Utils/StatelessRNG.cs
+++ b/osu.Game/Utils/StatelessRNG.cs
@@ -1,6 +1,8 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
+
 namespace osu.Game.Utils
 {
     /// <summary>
@@ -22,7 +24,7 @@ private static ulong mix(ulong x)
         }
 
         /// <summary>
-        /// Compute an integer from given seed and series number.
+        /// Generate a random 64-bit unsigned integer from given seed.
         /// </summary>
         /// <param name="seed">
         /// The seed value of this random number generator.
@@ -31,11 +33,39 @@ private static ulong mix(ulong x)
         /// The series number.
         /// Different values are computed for the same seed in different series.
         /// </param>
-        public static ulong Get(int seed, int series = 0) =>
-            unchecked(mix(((ulong)(uint)series << 32) | ((uint)seed ^ 0x12345678)));
+        public static ulong NextUlong(int seed, int series = 0)
+        {
+            unchecked
+            {
+                //
+                var combined = ((ulong)(uint)series << 32) | (uint)seed;
+                // The xor operation is to not map (0, 0) to 0.
+                return mix(combined ^ 0x12345678);
+            }
+        }
 
         /// <summary>
-        /// Compute a floating point value between 0 and 1 (excluding 1) from given seed and series number.
+        /// Generate a random integer in range [0, maxValue) from given seed.
+        /// </summary>
+        /// <param name="maxValue">
+        /// The number of possible results.
+        /// </param>
+        /// <param name="seed">
+        /// The seed value of this random number generator.
+        /// </param>
+        /// <param name="series">
+        /// The series number.
+        /// Different values are computed for the same seed in different series.
+        /// </param>
+        public static int NextInt(int maxValue, int seed, int series = 0)
+        {
+            if (maxValue <= 0) throw new ArgumentOutOfRangeException(nameof(maxValue));
+
+            return (int)(NextUlong(seed, series) % (ulong)maxValue);
+        }
+
+        /// <summary>
+        /// Compute a random floating point value between 0 and 1 (excluding 1) from given seed and series number.
         /// </summary>
         /// <param name="seed">
         /// The seed value of this random number generator.
@@ -44,7 +74,7 @@ public static ulong Get(int seed, int series = 0) =>
         /// The series number.
         /// Different values are computed for the same seed in different series.
         /// </param>
-        public static float GetSingle(int seed, int series = 0) =>
-            (float)(Get(seed, series) & ((1 << 24) - 1)) / (1 << 24); // float has 24-bit precision
+        public static float NextSingle(int seed, int series = 0) =>
+            (float)(NextUlong(seed, series) & ((1 << 24) - 1)) / (1 << 24); // float has 24-bit precision
     }
 }