mirror of
https://github.com/diasurgical/DevilutionX.git
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409 lines
13 KiB
C++
409 lines
13 KiB
C++
/**
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* @file random.hpp
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*
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* Contains convenience functions for random number generation
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*
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* This includes specific engine/distribution functions for logic that needs to be compatible with the base game.
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*/
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#pragma once
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#include <algorithm>
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#include <cstdint>
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#include <initializer_list>
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#include <random>
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namespace devilution {
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class DiabloGenerator {
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private:
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/** Borland C/C++ psuedo-random number generator needed for vanilla compatibility */
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std::linear_congruential_engine<uint32_t, 0x015A4E35, 1, 0> lcg;
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public:
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/**
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* @brief Set the state of the RandomNumberEngine used by the base game to the specific seed
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* @param seed New engine state
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*/
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DiabloGenerator(uint32_t seed)
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{
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lcg.seed(seed);
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}
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/**
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* @brief Advance the global RandomNumberEngine state by the specified number of rounds
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*
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* Only used to maintain vanilla compatibility until logic requiring reproducible random number generation is isolated.
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* @param count How many values to discard
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*/
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void discardRandomValues(unsigned count)
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{
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lcg.discard(count);
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}
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/**
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* @brief Generates a random non-negative integer (most of the time) using the vanilla RNG
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*
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* This advances the engine state then interprets the new engine state as a signed value and calls std::abs to try
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* discard the high bit of the result. This usually returns a positive number but may very rarely return -2^31.
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*
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* This function is only used when the base game wants to store the seed used to generate an item or level, however
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* as the returned value is transformed about 50% of values do not reflect the actual engine state. It would be more
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* appropriate to use GetLCGEngineState() in these cases but that may break compatibility with the base game.
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*
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* @return A random number in the range [0,2^31) or -2^31
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*/
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int32_t advanceRndSeed()
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{
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const int32_t seed = static_cast<int32_t>(lcg());
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// since abs(INT_MIN) is undefined behavior, handle this value specially
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return seed == std::numeric_limits<int32_t>::min() ? std::numeric_limits<int32_t>::min() : std::abs(seed);
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}
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/**
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* @brief Generates a random integer less than the given limit using the vanilla RNG
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*
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* If v is not a positive number this function returns 0 without calling the RNG.
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*
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* Limits between 32768 and 65534 should be avoided as a bug in vanilla means this function always returns a value
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* less than 32768 for limits in that range.
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*
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* This can very rarely return a negative value in the range (-v, -1] due to the bug in AdvanceRndSeed()
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*
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* @see AdvanceRndSeed()
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* @param v The upper limit for the return value
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* @return A random number in the range [0, v) or rarely a negative value in (-v, -1]
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*/
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int32_t generateRnd(int32_t v)
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{
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if (v <= 0)
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return 0;
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if (v <= 0x7FFF) // use the high bits to correct for LCG bias
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return (advanceRndSeed() >> 16) % v;
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return advanceRndSeed() % v;
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}
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/**
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* @brief Generates a random boolean value using the vanilla RNG
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*
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* This function returns true 1 in `frequency` of the time, otherwise false. For example the default frequency of 2
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* represents a 50/50 chance.
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*
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* @param frequency odds of returning a true value
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* @return A random boolean value
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*/
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bool flipCoin(unsigned frequency)
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{
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// Casting here because GenerateRnd takes a signed argument when it should take and yield unsigned.
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return generateRnd(static_cast<int32_t>(frequency)) == 0;
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}
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/**
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* @brief Picks one of the elements in the list randomly.
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*
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* @param values The values to pick from
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* @return A random value from the 'values' list.
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*/
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template <typename T>
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const T pickRandomlyAmong(const std::initializer_list<T> &values)
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{
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const auto index { std::max<int32_t>(generateRnd(static_cast<int32_t>(values.size())), 0) };
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return *(values.begin() + index);
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}
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/**
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* @brief Generates a random non-negative integer
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*
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* Effectively the same as GenerateRnd but will never return a negative value
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* @param v upper limit for the return value
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* @return a value between 0 and v-1 inclusive, i.e. the range [0, v)
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*/
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inline int32_t randomIntLessThan(int32_t v)
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{
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return std::max<int32_t>(generateRnd(v), 0);
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}
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/**
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* @brief Randomly chooses a value somewhere within the given range
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* @param min lower limit, minimum possible value
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* @param max upper limit, either the maximum possible value for a closed range (the default behaviour) or one greater than the maximum value for a half-open range
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* @param halfOpen whether to use the limits as a half-open range or not
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* @return a randomly selected integer
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*/
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inline int32_t randomIntBetween(int32_t min, int32_t max, bool halfOpen = false)
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{
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return randomIntLessThan(max - min + (halfOpen ? 0 : 1)) + min;
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}
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};
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// Based on fmix32 implementation from MurmurHash3 created by Austin Appleby in 2008
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// https://github.com/aappleby/smhasher/blob/61a0530f28277f2e850bfc39600ce61d02b518de/src/MurmurHash3.cpp#L68
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// and adapted from https://prng.di.unimi.it/splitmix64.c written in 2015 by Sebastiano Vigna
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//
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// See also:
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// Guy L. Steele, Doug Lea, and Christine H. Flood. 2014.
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// Fast splittable pseudorandom number generators. SIGPLAN Not. 49, 10 (October 2014), 453–472.
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// https://doi.org/10.1145/2714064.2660195
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class SplitMix32 {
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uint32_t state;
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public:
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SplitMix32(uint32_t state)
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: state(state)
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{
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}
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uint32_t next()
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{
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uint32_t z = (state += 0x9e3779b9);
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z = (z ^ (z >> 16)) * 0x85ebca6b;
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z = (z ^ (z >> 13)) * 0xc2b2ae35;
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return z ^ (z >> 16);
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}
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void generate(uint32_t *begin, const uint32_t *end)
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{
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while (begin != end) {
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*begin = next();
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++begin;
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}
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}
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};
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// Adapted from https://prng.di.unimi.it/splitmix64.c written in 2015 by Sebastiano Vigna
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//
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// See also:
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// Guy L. Steele, Doug Lea, and Christine H. Flood. 2014.
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// Fast splittable pseudorandom number generators. SIGPLAN Not. 49, 10 (October 2014), 453–472.
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// https://doi.org/10.1145/2714064.2660195
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class SplitMix64 {
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uint64_t state;
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public:
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SplitMix64(uint64_t state)
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: state(state)
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{
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}
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uint64_t next()
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{
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uint64_t z = (state += 0x9e3779b97f4a7c15);
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z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
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z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
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return z ^ (z >> 31);
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}
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void generate(uint64_t *begin, const uint64_t *end)
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{
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while (begin != end) {
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*begin = next();
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++begin;
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}
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}
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};
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/** Adapted from https://prng.di.unimi.it/xoshiro128plusplus.c written in 2019 by David Blackman and Sebastiano Vigna */
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class xoshiro128plusplus {
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public:
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typedef uint32_t state[4];
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xoshiro128plusplus() { seed(); }
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xoshiro128plusplus(const state &s) { copy(this->s, s); }
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xoshiro128plusplus(uint64_t initialSeed) { seed(initialSeed); }
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xoshiro128plusplus(uint32_t initialSeed) { seed(initialSeed); }
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uint32_t next();
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/* This is the jump function for the generator. It is equivalent
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to 2^64 calls to next(); it can be used to generate 2^64
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non-overlapping subsequences for parallel computations. */
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void jump()
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{
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static constexpr uint32_t JUMP[] = { 0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b };
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uint32_t s0 = 0;
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uint32_t s1 = 0;
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uint32_t s2 = 0;
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uint32_t s3 = 0;
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for (const uint32_t entry : JUMP)
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for (int b = 0; b < 32; b++) {
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if (entry & UINT32_C(1) << b) {
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s0 ^= s[0];
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s1 ^= s[1];
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s2 ^= s[2];
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s3 ^= s[3];
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}
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next();
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}
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s[0] = s0;
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s[1] = s1;
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s[2] = s2;
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s[3] = s3;
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}
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void save(state &s) const
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{
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copy(s, this->s);
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}
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private:
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state s;
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void seed(uint64_t value)
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{
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uint64_t seeds[2];
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SplitMix64 seedSequence { value };
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seedSequence.generate(seeds, seeds + 2);
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s[0] = static_cast<uint32_t>(seeds[0] >> 32);
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s[1] = static_cast<uint32_t>(seeds[0]);
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s[2] = static_cast<uint32_t>(seeds[1] >> 32);
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s[3] = static_cast<uint32_t>(seeds[1]);
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}
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void seed(uint32_t value)
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{
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SplitMix32 seedSequence { value };
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seedSequence.generate(s, s + 4);
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}
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void seed()
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{
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seed(timeSeed());
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// AmigaOS has no entropy source backing std::random_device; constructing it
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// aborts, and this runs during static initialization, so the process dies
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// before main().
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#if !(defined(WINVER) && WINVER <= 0x0500 && (!defined(_WIN32_WINNT) || _WIN32_WINNT == 0)) && !defined(__amigaos__)
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static std::random_device rd;
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std::uniform_int_distribution<uint32_t> dist;
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for (uint32_t &cell : s)
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cell ^= dist(rd);
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#endif
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}
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static uint64_t timeSeed();
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static void copy(state &dst, const state &src);
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};
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/**
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* @brief Returns a copy of the global seed generator and fast-forwards the global seed generator to avoid collisions
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*/
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xoshiro128plusplus ReserveSeedSequence();
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/**
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* @brief Advances the global seed generator state and returns the new value
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*/
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uint32_t GenerateSeed();
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/**
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* @brief Set the state of the RandomNumberEngine used by the base game to the specific seed
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* @param seed New engine state
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*/
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void SetRndSeed(uint32_t seed);
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/**
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* @brief Returns the current state of the RandomNumberEngine used by the base game
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*
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* This is only exposed to allow for debugging vanilla code and testing. Using this engine for new code is discouraged
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* due to the poor randomness and bugs in the implementation that need to be retained for compatibility.
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*
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* @return The current engine state
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*/
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uint32_t GetLCGEngineState();
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/**
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* @brief Advance the global RandomNumberEngine state by the specified number of rounds
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*
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* Only used to maintain vanilla compatibility until logic requiring reproducible random number generation is isolated.
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* @param count How many values to discard
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*/
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void DiscardRandomValues(unsigned count);
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/**
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* @brief Advances the global RandomNumberEngine state and returns the new value
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*/
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uint32_t GenerateRandomNumber();
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/**
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* @brief Generates a random non-negative integer (most of the time) using the vanilla RNG
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*
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* This advances the engine state then interprets the new engine state as a signed value and calls std::abs to try
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* discard the high bit of the result. This usually returns a positive number but may very rarely return -2^31.
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*
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* This function is only used when the base game wants to store the seed used to generate an item or level, however
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* as the returned value is transformed about 50% of values do not reflect the actual engine state. It would be more
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* appropriate to use GetLCGEngineState() in these cases but that may break compatibility with the base game.
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*
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* @return A random number in the range [0,2^31) or -2^31
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*/
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[[nodiscard]] int32_t AdvanceRndSeed();
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/**
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* @brief Generates a random integer less than the given limit using the vanilla RNG
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*
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* If v is not a positive number this function returns 0 without calling the RNG.
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*
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* Limits between 32768 and 65534 should be avoided as a bug in vanilla means this function always returns a value
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* less than 32768 for limits in that range.
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*
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* This can very rarely return a negative value in the range (-v, -1] due to the bug in AdvanceRndSeed()
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*
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* @see AdvanceRndSeed()
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* @param v The upper limit for the return value
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* @return A random number in the range [0, v) or rarely a negative value in (-v, -1]
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*/
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int32_t GenerateRnd(int32_t v);
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/**
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* @brief Generates a random boolean value using the vanilla RNG
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*
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* This function returns true 1 in `frequency` of the time, otherwise false. For example the default frequency of 2
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* represents a 50/50 chance.
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*
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* @param frequency odds of returning a true value
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* @return A random boolean value
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*/
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bool FlipCoin(unsigned frequency = 2);
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/**
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* @brief Picks one of the elements in the list randomly.
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*
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* @param values The values to pick from
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* @return A random value from the 'values' list.
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*/
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template <typename T>
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const T PickRandomlyAmong(const std::initializer_list<T> &values)
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{
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const auto index { std::max<int32_t>(GenerateRnd(static_cast<int32_t>(values.size())), 0) };
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return *(values.begin() + index);
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}
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/**
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* @brief Generates a random non-negative integer
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*
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* Effectively the same as GenerateRnd but will never return a negative value
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* @param v upper limit for the return value
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* @return a value between 0 and v-1 inclusive, i.e. the range [0, v)
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*/
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inline int32_t RandomIntLessThan(int32_t v)
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{
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return std::max<int32_t>(GenerateRnd(v), 0);
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}
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/**
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* @brief Randomly chooses a value somewhere within the given range
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* @param min lower limit, minimum possible value
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* @param max upper limit, either the maximum possible value for a closed range (the default behaviour) or one greater than the maximum value for a half-open range
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* @param halfOpen whether to use the limits as a half-open range or not
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* @return a randomly selected integer
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*/
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inline int32_t RandomIntBetween(int32_t min, int32_t max, bool halfOpen = false)
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{
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return RandomIntLessThan(max - min + (halfOpen ? 0 : 1)) + min;
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}
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} // namespace devilution
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