35 lines
1.6 KiB
C#
35 lines
1.6 KiB
C#
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
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using Random = CultMath.Random;
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// Structured simulation seeds: the one place a zone seed, a stream and an ordinal become a generator. Every
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// draw is a pure function of its arguments, never of a shared stream, so one roll cannot perturb another.
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public static class SimulationDice
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{
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public const uint LootStream = 1;
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public const uint MineStream = 2;
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// 9.1 (docs/fire-control-cut.md): fmix32, MurmurHash3's 32-bit finalizer -- xor-shift, multiply,
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// xor-shift, multiply, xor-shift. Diffuses a structured seed (a zone seed XORed with a small,
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// low-bits-only id) across every bit before the first xorshift draw reads it, so two seeds that differ
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// only in their low bits still land on uncorrelated first outputs. Caller-side mixing only --
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// CultMath.Random itself is unchanged. FireControl.Commit's per-shot seed is built on this verbatim.
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public static uint Mix(uint seed)
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{
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seed ^= seed >> 16;
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seed *= 0x85ebca6bu;
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seed ^= seed >> 13;
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seed *= 0xc2b2ae35u;
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seed ^= seed >> 16;
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return seed;
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}
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// The generator for the `ordinal`th roll of `stream` in the zone identified by `zoneSeed`.
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public static Random For(uint zoneSeed, uint stream, uint ordinal)
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{
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var seed = Mix(Mix(zoneSeed ^ Mix(stream)) ^ ordinal);
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return new Random(seed == 0 ? 1u : seed);
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}
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}
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