| | | 1 | | //======================================================================= |
| | | 2 | | // DeterministicRandom.cs |
| | | 3 | | //======================================================================= |
| | | 4 | | // MIT License, Copyright (c) 2024–present David Oravsky (mrdav30) |
| | | 5 | | // See LICENSE file in the project root for full license information. |
| | | 6 | | //======================================================================= |
| | | 7 | | |
| | | 8 | | using System; |
| | | 9 | | using System.Runtime.CompilerServices; |
| | | 10 | | |
| | | 11 | | namespace FixedMathSharp.Random |
| | | 12 | | { |
| | | 13 | | /// <summary> |
| | | 14 | | /// Fast, seedable, deterministic RNG suitable for lockstep sims and map gen. |
| | | 15 | | /// Uses xoroshiro128++ with splitmix64 seeding. No allocations, no time/GUID. |
| | | 16 | | /// </summary> |
| | | 17 | | public struct DeterministicRandom |
| | | 18 | | { |
| | | 19 | | // xoroshiro128++ state |
| | | 20 | | private ulong _s0; |
| | | 21 | | private ulong _s1; |
| | | 22 | | |
| | | 23 | | #region Construction / Seeding |
| | | 24 | | |
| | | 25 | | /// <summary> |
| | | 26 | | /// Initializes a new instance of the DeterministicRandom class using the specified seed value. |
| | | 27 | | /// </summary> |
| | | 28 | | /// <remarks> |
| | | 29 | | /// This constructor expands the provided seed into the internal state required for deterministic random number |
| | | 30 | | /// The generated sequence is fully determined by the seed value. |
| | | 31 | | /// </remarks> |
| | | 32 | | /// <param name="seed"> |
| | | 33 | | /// The initial seed value used to generate the internal state. |
| | | 34 | | /// Using the same seed will produce the same sequence of random numbers. |
| | | 35 | | /// </param> |
| | | 36 | | public DeterministicRandom(ulong seed) |
| | | 37 | | { |
| | | 38 | | // Expand a single seed into two 64-bit state words via splitmix64. |
| | 27 | 39 | | _s0 = SplitMix64(ref seed); |
| | 27 | 40 | | _s1 = SplitMix64(ref seed); |
| | 27 | 41 | | } |
| | | 42 | | |
| | | 43 | | /// <summary> |
| | | 44 | | /// Create a stream deterministically |
| | | 45 | | /// Derived from (worldSeed, featureKey[,index]). |
| | | 46 | | /// </summary> |
| | | 47 | | public static DeterministicRandom FromWorldFeature(ulong worldSeed, ulong featureKey, ulong index = 0) |
| | | 48 | | { |
| | | 49 | | // Simple reversible mix (swap for a stronger mix if required). |
| | 4 | 50 | | ulong seed = Mix64(worldSeed, featureKey); |
| | 4 | 51 | | seed = Mix64(seed, index); |
| | 4 | 52 | | return new DeterministicRandom(seed); |
| | | 53 | | } |
| | | 54 | | |
| | | 55 | | #endregion |
| | | 56 | | |
| | | 57 | | #region Core PRNG |
| | | 58 | | |
| | | 59 | | /// <summary> |
| | | 60 | | /// xoroshiro128++ next 64 bits. |
| | | 61 | | /// </summary> |
| | | 62 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 63 | | public ulong NextU64() |
| | | 64 | | { |
| | 95574 | 65 | | ulong s0 = _s0, s1 = _s1; |
| | 47787 | 66 | | ulong result = RotL(s0 + s1, 17) + s0; |
| | | 67 | | |
| | 47787 | 68 | | s1 ^= s0; |
| | 47787 | 69 | | _s0 = RotL(s0, 49) ^ s1 ^ (s1 << 21); // a,b |
| | 47787 | 70 | | _s1 = RotL(s1, 28); // c |
| | | 71 | | |
| | 47787 | 72 | | return result; |
| | | 73 | | } |
| | | 74 | | |
| | | 75 | | /// <summary> |
| | | 76 | | /// Next non-negative Int32 in [0, int.MaxValue]. |
| | | 77 | | /// </summary> |
| | | 78 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 79 | | public int Next() |
| | | 80 | | { |
| | | 81 | | // Take high bits for better quality; mask to 31 bits non-negative. |
| | 1004 | 82 | | return (int)(NextU64() >> 33); |
| | | 83 | | } |
| | | 84 | | |
| | | 85 | | /// <summary> |
| | | 86 | | /// Unbiased int in [0, maxExclusive). |
| | | 87 | | /// </summary> |
| | | 88 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 89 | | public int Next(int maxExclusive) |
| | | 90 | | { |
| | 30214 | 91 | | return maxExclusive <= 0 |
| | 30214 | 92 | | ? throw new ArgumentOutOfRangeException(nameof(maxExclusive)) |
| | 30214 | 93 | | : (int)NextBounded((uint)maxExclusive); |
| | | 94 | | } |
| | | 95 | | |
| | | 96 | | /// <summary> |
| | | 97 | | /// Unbiased int in [min, maxExclusive). |
| | | 98 | | /// </summary> |
| | | 99 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 100 | | public int Next(int minInclusive, int maxExclusive) |
| | | 101 | | { |
| | 4101 | 102 | | if (minInclusive >= maxExclusive) |
| | 3 | 103 | | throw new ArgumentException("min >= max"); |
| | | 104 | | |
| | 4098 | 105 | | uint range = (uint)(maxExclusive - minInclusive); |
| | 4098 | 106 | | return minInclusive + (int)NextBounded(range); |
| | | 107 | | } |
| | | 108 | | |
| | | 109 | | /// <summary> |
| | | 110 | | /// Fill span with random bytes. |
| | | 111 | | /// </summary> |
| | | 112 | | public void NextBytes(Span<byte> buffer) |
| | | 113 | | { |
| | 13 | 114 | | int i = 0; |
| | 34 | 115 | | while (i + 8 <= buffer.Length) |
| | | 116 | | { |
| | 21 | 117 | | ulong v = NextU64(); |
| | 21 | 118 | | Unsafe.WriteUnaligned(ref buffer[i], v); |
| | 21 | 119 | | i += 8; |
| | | 120 | | } |
| | 13 | 121 | | if (i < buffer.Length) |
| | | 122 | | { |
| | 10 | 123 | | ulong v = NextU64(); |
| | 47 | 124 | | while (i < buffer.Length) |
| | | 125 | | { |
| | 37 | 126 | | buffer[i++] = (byte)v; |
| | 37 | 127 | | v >>= 8; |
| | | 128 | | } |
| | | 129 | | } |
| | 13 | 130 | | } |
| | | 131 | | |
| | | 132 | | #endregion |
| | | 133 | | |
| | | 134 | | #region Fixed64 helpers |
| | | 135 | | |
| | | 136 | | /// <summary> |
| | | 137 | | /// Random Fixed64 in [0,1). |
| | | 138 | | /// </summary> |
| | | 139 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 140 | | public Fixed64 NextFixed6401() |
| | | 141 | | { |
| | | 142 | | // Produce a raw value in [0, One.m_rawValue) |
| | 4096 | 143 | | ulong rawOne = (ulong)Fixed64.One.m_rawValue; |
| | 4096 | 144 | | ulong r = NextBounded(rawOne); |
| | 4096 | 145 | | return Fixed64.FromRaw((long)r); |
| | | 146 | | } |
| | | 147 | | |
| | | 148 | | /// <summary> |
| | | 149 | | /// Random Fixed64 in [0, maxExclusive). |
| | | 150 | | /// </summary> |
| | | 151 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 152 | | public Fixed64 NextFixed64(Fixed64 maxExclusive) |
| | | 153 | | { |
| | 4098 | 154 | | if (maxExclusive <= Fixed64.Zero) |
| | 2 | 155 | | throw new ArgumentOutOfRangeException(nameof(maxExclusive), "max must be > 0"); |
| | | 156 | | |
| | 4096 | 157 | | ulong rawMax = (ulong)maxExclusive.m_rawValue; |
| | 4096 | 158 | | ulong r = NextBounded(rawMax); |
| | 4096 | 159 | | return Fixed64.FromRaw((long)r); |
| | | 160 | | } |
| | | 161 | | |
| | | 162 | | /// <summary> |
| | | 163 | | /// Random Fixed64 in [minInclusive, maxExclusive). |
| | | 164 | | /// </summary> |
| | | 165 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 166 | | public Fixed64 NextFixed64(Fixed64 minInclusive, Fixed64 maxExclusive) |
| | | 167 | | { |
| | 4101 | 168 | | if (minInclusive >= maxExclusive) |
| | 2 | 169 | | throw new ArgumentException("min >= max"); |
| | | 170 | | |
| | 4099 | 171 | | ulong span = (ulong)(maxExclusive.m_rawValue - minInclusive.m_rawValue); |
| | 4099 | 172 | | ulong r = NextBounded(span); |
| | 4099 | 173 | | return Fixed64.FromRaw((long)r + minInclusive.m_rawValue); |
| | | 174 | | } |
| | | 175 | | |
| | | 176 | | #endregion |
| | | 177 | | |
| | | 178 | | #region Internals: unbiased range, splitmix64, mixing, rotations |
| | | 179 | | |
| | | 180 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 181 | | private ulong NextBounded(ulong bound) |
| | | 182 | | { |
| | | 183 | | // Rejection to avoid modulo bias. |
| | | 184 | | // threshold = 2^64 % bound, but expressed as (-bound) % bound |
| | 46601 | 185 | | ulong threshold = unchecked((ulong)-(long)bound) % bound; |
| | | 186 | | while (true) |
| | | 187 | | { |
| | 46602 | 188 | | ulong r = NextU64(); |
| | 46602 | 189 | | if (r >= threshold) |
| | 46601 | 190 | | return r % bound; |
| | | 191 | | } |
| | | 192 | | } |
| | | 193 | | |
| | | 194 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | 143361 | 195 | | private static ulong RotL(ulong x, int k) => (x << k) | (x >> (64 - k)); |
| | | 196 | | |
| | | 197 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 198 | | private static ulong SplitMix64(ref ulong state) |
| | | 199 | | { |
| | 54 | 200 | | ulong z = (state += 0x9E3779B97F4A7C15UL); |
| | 54 | 201 | | z = (z ^ (z >> 30)) * 0xBF58476D1CE4E5B9UL; |
| | 54 | 202 | | z = (z ^ (z >> 27)) * 0x94D049BB133111EBUL; |
| | 54 | 203 | | return z ^ (z >> 31); |
| | | 204 | | } |
| | | 205 | | |
| | | 206 | | [MethodImpl(MethodImplOptions.AggressiveInlining)] |
| | | 207 | | private static ulong Mix64(ulong a, ulong b) |
| | | 208 | | { |
| | | 209 | | // Simple reversible mix (variant of splitmix finalizer). |
| | 8 | 210 | | ulong x = a ^ (b + 0x9E3779B97F4A7C15UL); |
| | 8 | 211 | | x = (x ^ (x >> 30)) * 0xBF58476D1CE4E5B9UL; |
| | 8 | 212 | | x = (x ^ (x >> 27)) * 0x94D049BB133111EBUL; |
| | 8 | 213 | | return x ^ (x >> 31); |
| | | 214 | | } |
| | | 215 | | |
| | | 216 | | #endregion |
| | | 217 | | } |
| | | 218 | | } |