random: use TinyMT instead of XorShift

libraries/libstratosphere/include/stratosphere/util/util_tinymt.hpp

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2018-2019 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+#include <vapours.hpp>
+
+namespace ams::util {
+
+    /* Implementation of TinyMT (mersenne twister RNG). */
+    /* Like Nintendo, we will use the sample parameters. */
+    class TinyMT {
+        public:
+            static constexpr size_t NumStateWords = 4;
+
+            struct State {
+                u32 data[NumStateWords];
+            };
+        private:
+            static constexpr u32 ParamMat1  = 0x8F7011EE;
+            static constexpr u32 ParamMat2  = 0xFC78FF1F;
+            static constexpr u32 ParamTmat  = 0x3793FDFF;
+
+            static constexpr u32 ParamMult  = 0x6C078965;
+            static constexpr u32 ParamPlus  = 0x0019660D;
+            static constexpr u32 ParamXor   = 0x5D588B65;
+
+            static constexpr u32 TopBitmask = 0x7FFFFFFF;
+
+            static constexpr int MinimumInitIterations   = 8;
+            static constexpr int NumDiscardedInitOutputs = 8;
+        private:
+            State state;
+        private:
+            /* Internal API. */
+            void FinalizeInitialization();
+
+            u32 GenerateRandomU24() { return (this->GenerateRandomU32() >> 8); }
+
+            static void GenerateInitialValuePlus(TinyMT::State *state, int index, u32 value);
+            static void GenerateInitialValueXor(TinyMT::State *state, int index);
+        public:
+            /* Public API. */
+
+            /* Initialization. */
+            void Initialize(u32 seed);
+            void Initialize(const u32 *seed, int seed_count);
+
+            /* State management. */
+            void GetState(TinyMT::State *out) const;
+            void SetState(const TinyMT::State *state);
+
+            /* Random generation. */
+            void GenerateRandomBytes(void *dst, size_t size);
+            u32  GenerateRandomU32();
+
+            inline u64 GenerateRandomU64() {
+                const u32 lo = this->GenerateRandomU32();
+                const u32 hi = this->GenerateRandomU32();
+                return (static_cast<u64>(hi) << 32) | static_cast<u64>(lo);
+            }
+
+            inline float  GenerateRandomF32() {
+                /* Floats have 24 bits of mantissa. */
+                constexpr int MantissaBits = 24;
+                return GenerateRandomU24() * (1.0f / (1ul << MantissaBits));
+            }
+
+            inline double GenerateRandomF64() {
+                /* Doubles have 53 bits of mantissa. */
+                /* The smart way to generate 53 bits of random would be to use 32 bits */
+                /* from the first rnd32() call, and then 21 from the second. */
+                /* Nintendo does not. They use (32 - 5) = 27 bits from the first rnd32() */
+                /* call, and (32 - 6) bits from the second. We'll do what they do, but */
+                /* There's not a clear reason why. */
+                constexpr int MantissaBits = 53;
+                constexpr int Shift1st  = (64 - MantissaBits) / 2;
+                constexpr int Shift2nd  = (64 - MantissaBits) - Shift1st;
+
+                const u32 first  = (this->GenerateRandomU32() >> Shift1st);
+                const u32 second = (this->GenerateRandomU32() >> Shift2nd);
+
+                return (1.0 * first * (1ul << (32 - Shift2nd)) + second) * (1.0 / (1ul << MantissaBits));
+            }
+    };
+
+}