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Sync RNG in multiplayer #7098

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Sync RNG in multiplayer #7098

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f7e0ba0
Refactor/revise PVP functions
kphoenix137 Apr 21, 2024
c9eaf3f
Sync RNG
kphoenix137 Apr 21, 2024
2d8765b
refactor
kphoenix137 Apr 21, 2024
8b1b869
Add sync to rng calls
kphoenix137 Apr 21, 2024
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25 changes: 20 additions & 5 deletions Source/engine/random.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,9 @@
#include <limits>
#include <random>

#include <msg.h>
#include <player.h>

namespace devilution {

/** Current game seed */
Expand Down Expand Up @@ -38,20 +41,32 @@ uint32_t GenerateSeed()
return sglGameSeed;
}

int32_t AdvanceRndSeed()
int32_t AdvanceRndSeed(bool sync /*= false*/)
{
const int32_t seed = static_cast<int32_t>(GenerateSeed());
if (sync) {
for (const auto &player : Players) {
if (&player == nullptr)
continue;
// Active player with the lowest player ID will be in charge of RNG state.
if (player.plractive && &player != MyPlayer) {
break;
}
NetSendCmdSyncSeed(true, GetLCGEngineState());
}
}
const auto seed = static_cast<int32_t>(GenerateSeed());

// since abs(INT_MIN) is undefined behavior, handle this value specially
return seed == std::numeric_limits<int32_t>::min() ? std::numeric_limits<int32_t>::min() : std::abs(seed);
}

int32_t GenerateRnd(int32_t v)
int32_t GenerateRnd(int32_t v, bool sync /*= false*/)
{
if (v <= 0)
return 0;
if (v <= 0x7FFF) // use the high bits to correct for LCG bias
return (AdvanceRndSeed() >> 16) % v;
return AdvanceRndSeed() % v;
return (AdvanceRndSeed(sync) >> 16) % v;
return AdvanceRndSeed(sync) % v;
}

bool FlipCoin(unsigned frequency)
Expand Down
12 changes: 6 additions & 6 deletions Source/engine/random.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,7 @@ uint32_t GenerateSeed();
*
* @return A random number in the range [0,2^31) or -2^31
*/
[[nodiscard]] int32_t AdvanceRndSeed();
[[nodiscard]] int32_t AdvanceRndSeed(bool sync = false);

/**
* @brief Generates a random integer less than the given limit using the vanilla RNG
Expand All @@ -193,7 +193,7 @@ uint32_t GenerateSeed();
* @param v The upper limit for the return value
* @return A random number in the range [0, v) or rarely a negative value in (-v, -1]
*/
int32_t GenerateRnd(int32_t v);
int32_t GenerateRnd(int32_t v, bool sync = false);

/**
* @brief Generates a random boolean value using the vanilla RNG
Expand Down Expand Up @@ -227,9 +227,9 @@ const T PickRandomlyAmong(const std::initializer_list<T> &values)
* @param v upper limit for the return value
* @return a value between 0 and v-1 inclusive, i.e. the range [0, v)
*/
inline int32_t RandomIntLessThan(int32_t v)
inline int32_t RandomIntLessThan(int32_t v, bool sync = false)
{
return std::max<int32_t>(GenerateRnd(v), 0);
return std::max<int32_t>(GenerateRnd(v, sync), 0);
}

/**
Expand All @@ -239,9 +239,9 @@ inline int32_t RandomIntLessThan(int32_t v)
* @param halfOpen whether to use the limits as a half-open range or not
* @return a randomly selected integer
*/
inline int32_t RandomIntBetween(int32_t min, int32_t max, bool halfOpen = false)
inline int32_t RandomIntBetween(int32_t min, int32_t max, bool halfOpen = false, bool sync = false)
{
return RandomIntLessThan(max - min + (halfOpen ? 0 : 1)) + min;
return RandomIntLessThan(max - min + (halfOpen ? 0 : 1), sync) + min;
}

} // namespace devilution
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