From 2ccaefd9b0896d46833aff3fb5ebb03e1a2cb71d Mon Sep 17 00:00:00 2001 From: NepDisk Date: Sun, 24 Aug 2025 11:35:33 -0400 Subject: [PATCH] Try some things to reduce rng biases This with no PRNG classes: https://git.do.srb2.org/KartKrew/RingRacers/-/commit/492c068cdddafb3d22c1ad1c3959bf757b862eed --- src/lua_baselib.c | 8 +-- src/m_random.c | 126 ++++++++++++++++++++++++++++++++++++---------- src/m_random.h | 16 +++--- src/st_stuff.c | 4 +- 4 files changed, 112 insertions(+), 42 deletions(-) diff --git a/src/lua_baselib.c b/src/lua_baselib.c index 9896d9c08..e2f166679 100644 --- a/src/lua_baselib.c +++ b/src/lua_baselib.c @@ -435,10 +435,7 @@ static int lib_pRandomByte(lua_State *L) static int lib_pRandomKey(lua_State *L) { INT32 a = (INT32)luaL_checkinteger(L, 1); - NOHUD - if (a > 65536) - LUA_UsageWarning(L, "P_RandomKey: range > 65536 is undefined behavior"); lua_pushinteger(L, P_RandomKey(a)); demo_writerng = 2; return 1; @@ -450,13 +447,12 @@ static int lib_pRandomRange(lua_State *L) INT32 b = (INT32)luaL_checkinteger(L, 2); NOHUD - if (b < a) { + if (b < a) + { INT32 c = a; a = b; b = c; } - if ((b-a+1) > 65536) - LUA_UsageWarning(L, "P_RandomRange: range > 65536 is undefined behavior"); lua_pushinteger(L, P_RandomRange(a, b)); demo_writerng = 2; return 1; diff --git a/src/m_random.c b/src/m_random.c index 0e559dd80..43304d282 100644 --- a/src/m_random.c +++ b/src/m_random.c @@ -25,6 +25,49 @@ // RNG functions (not synched) // --------------------------- +ATTRINLINE static UINT32 FUNCINLINE __external_prng__(void) +{ + UINT32 rnd = rand(); + + #if RAND_MAX < 65535 + // Compensate for especially bad randomness. + UINT32 rndv = (rand() & 1) << 15; + rnd ^= rndv; + #endif + + // Shuffle like we do for our own PRNG, since RAND_MAX + // tends to be [0, INT32_MAX] instead of [0, UINT32_MAX]. + rnd ^= rnd >> 13; + rnd ^= rnd >> 11; + rnd ^= rnd << 21; + return (rnd * 36548569); +} + +ATTRINLINE static UINT32 FUNCINLINE __external_prng_bound__(UINT32 bound) +{ + // Do rejection sampling to remove the modulo bias. + UINT32 threshold = -bound % bound; + for (;;) + { + UINT32 r = __external_prng__(); + if (r >= threshold) + { + return r % bound; + } + } +} + +/** Provides a random 32-bit number. Distribution is uniform. + * As with all M_Random functions, not synched in netgames. + * + * \return A random 32-bit number. + */ +UINT32 M_Random(void) +{ + return __external_prng__(); +} + + /** Provides a random fixed point number. Distribution is uniform. * As with all M_Random functions, not synched in netgames. * @@ -32,13 +75,7 @@ */ fixed_t M_RandomFixed(void) { -#if RAND_MAX < 65535 - // Compensate for insufficient randomness. - fixed_t rndv = (rand()&1)<<15; - return rand()^rndv; -#else - return (rand() & 0xFFFF); -#endif + return (fixed_t)(__external_prng_bound__(FRACUNIT)); } /** Provides a random byte. Distribution is uniform. @@ -48,7 +85,7 @@ fixed_t M_RandomFixed(void) */ UINT8 M_RandomByte(void) { - return (rand() & 0xFF); + return (UINT8)(__external_prng_bound__(UINT8_MAX)); } /** Provides a random integer for picking random elements from an array. @@ -58,9 +95,9 @@ UINT8 M_RandomByte(void) * \param a Number of items in array. * \return A random integer from [0,a). */ -INT32 M_RandomKey(INT32 a) +UINT32 M_RandomKey(UINT32 a) { - return (INT32)((rand()/((unsigned)RAND_MAX+1.0f))*a); + return __external_prng_bound__(a); } /** Provides a random integer in a given range. @@ -73,7 +110,7 @@ INT32 M_RandomKey(INT32 a) */ INT32 M_RandomRange(INT32 a, INT32 b) { - return (INT32)((rand()/((unsigned)RAND_MAX+1.0f))*(b-a+1))+a; + return (INT32)(__external_prng_bound__((b - a) + 1)) + a; } @@ -88,24 +125,59 @@ static UINT32 randomseed = 0xBADE4404; // Holds the INITIAL seed value. Used for demos, possibly other debugging. static UINT32 initialseed = 0xBADE4404; -/** Provides a random fixed point number. +/** Provides a random 32 bit integer. * This is a variant of an xorshift PRNG; state fits in a 32 bit integer structure. * - * \return A random fixed point number from [0,1). + * \return A random, uniformly distributed number from [0,UINT32_MAX]. */ -ATTRINLINE static fixed_t FUNCINLINE __internal_prng__(void) +ATTRINLINE static UINT32 FUNCINLINE __internal_prng__(void) { randomseed ^= randomseed >> 13; randomseed ^= randomseed >> 11; randomseed ^= randomseed << 21; - return ( (randomseed*36548569) >> 4) & (FRACUNIT-1); + return (randomseed*36548569); +} + +/** Provides a random number within a specified range. + * + * \return A random, uniformly distributed number from [0,bound]. + */ +ATTRINLINE static UINT32 FUNCINLINE __internal_prng_bound__(UINT32 bound) +{ + // Do rejection sampling to remove the modulo bias. + UINT32 threshold = -bound % bound; + for (;;) + { + UINT32 r = __internal_prng__(); + if (r >= threshold) + { + return r % bound; + } + } } /** Provides a random fixed point number. Distribution is uniform. * Literally a wrapper for the internal PRNG function. * - * \return A random fixed point number from [0,1). + * \return A random fixed point number from [0,UINT32_MAX]. */ + +#ifndef DEBUGRANDOM +UINT32 P_Random(void) +{ +#else +UINT32 P_RandomD(const char *rfile, INT32 rline, pr_class_t pr_class) +{ + CONS_Printf("P_Random(%u) at: %sp %d\n", pr_class, rfile, rline); +#endif + return __internal_prng__(); +} + +/** Provides a random fixed point number. Distribution is uniform. + * + * \return A random fixed point number from [0,1]. + */ + #ifndef DEBUGRANDOM fixed_t P_RandomFixed(void) { @@ -114,14 +186,14 @@ fixed_t P_RandomFixedD(const char *rfile, INT32 rline) { CONS_Printf("P_RandomFixed() at: %sp %d\n", rfile, rline); #endif - return __internal_prng__(); + return (fixed_t)(__internal_prng_bound__(FRACUNIT)); } /** Provides a random byte. Distribution is uniform. * If you're curious, (&0xFF00) >> 8 gives the same result * as a fixed point multiplication by 256. * - * \return Random integer from [0, 255]. + * \return Random integer from [0,255]. * \sa __internal_prng__ */ #ifndef DEBUGRANDOM @@ -132,7 +204,7 @@ UINT8 P_RandomByteD(const char *rfile, INT32 rline) { CONS_Printf("P_RandomByte() at: %sp %d\n", rfile, rline); #endif - return (UINT8)((__internal_prng__()&0xFF00)>>8); + return (UINT8)(__internal_prng_bound__(UINT8_MAX)); } /** Provides a random integer for picking random elements from an array. @@ -140,18 +212,18 @@ UINT8 P_RandomByteD(const char *rfile, INT32 rline) * NOTE: Maximum range is 65536. * * \param a Number of items in array. - * \return A random integer from [0,a). + * \return A random integer from [0,a]. * \sa __internal_prng__ */ #ifndef DEBUGRANDOM -INT32 P_RandomKey(INT32 a) +UINT32 P_RandomKey(UINT32 a) { #else -INT32 P_RandomKeyD(const char *rfile, INT32 rline, INT32 a) +UINT32 P_RandomKeyD(const char *rfile, INT32 rline, UINT32 a) { CONS_Printf("P_RandomKey() at: %sp %d\n", rfile, rline); #endif - return (INT32)(((INT64)__internal_prng__() * a) >> FRACBITS); + return __internal_prng_bound__(a); } /** Provides a random integer in a given range. @@ -171,7 +243,7 @@ INT32 P_RandomRangeD(const char *rfile, INT32 rline, INT32 a, INT32 b) { CONS_Printf("P_RandomRange() at: %sp %d\n", rfile, rline); #endif - return (INT32)(((INT64)__internal_prng__() * (b-a+1)) >> FRACBITS) + a; + return (INT32)(__internal_prng_bound__((b - a) + 1)) + a; } @@ -183,13 +255,13 @@ INT32 P_RandomRangeD(const char *rfile, INT32 rline, INT32 a, INT32 b) /** Peeks to see what the next result from the PRNG will be. * Used for debugging. * - * \return A 'random' fixed point number from [0,1). + * \return A 'random' number from [0,UINT32_MAX] * \sa __internal_prng__ */ -fixed_t P_RandomPeek(void) +UINT32 P_RandomPeek(void) { UINT32 r = randomseed; - fixed_t ret = __internal_prng__(); + UINT32 ret = __internal_prng__(); randomseed = r; return ret; } diff --git a/src/m_random.h b/src/m_random.h index e7482d467..f706dd3b5 100644 --- a/src/m_random.h +++ b/src/m_random.h @@ -28,37 +28,41 @@ extern "C" { // P_Random functions pulls random bytes from a PRNG that is network synced. // RNG functions +UINT32 M_Random(void); fixed_t M_RandomFixed(void); UINT8 M_RandomByte(void); -INT32 M_RandomKey(INT32 a); +UINT32 M_RandomKey(UINT32 a); INT32 M_RandomRange(INT32 a, INT32 b); // PRNG functions #ifdef DEBUGRANDOM +#define P_Random() P_RandomD(__FILE__, __LINE__) #define P_RandomFixed() P_RandomFixedD(__FILE__, __LINE__) #define P_RandomByte() P_RandomByteD(__FILE__, __LINE__) #define P_RandomKey(c) P_RandomKeyD(__FILE__, __LINE__, c) #define P_RandomRange(c, d) P_RandomRangeD(__FILE__, __LINE__, c, d) +UINT32 P_RandomD(const char *rfile, INT32 rline); fixed_t P_RandomFixedD(const char *rfile, INT32 rline); UINT8 P_RandomByteD(const char *rfile, INT32 rline); -INT32 P_RandomKeyD(const char *rfile, INT32 rline, INT32 a); +UINT32 P_RandomKeyD(const char *rfile, INT32 rline, INT32 a); INT32 P_RandomRangeD(const char *rfile, INT32 rline, INT32 a, INT32 b); #else +UINT32 P_Random(void); fixed_t P_RandomFixed(void); UINT8 P_RandomByte(void); -INT32 P_RandomKey(INT32 a); +UINT32 P_RandomKey(UINT32 a); INT32 P_RandomRange(INT32 a, INT32 b); #endif // Macros for other functions -#define M_SignedRandom() ((INT32)M_RandomByte() - 128) // [-128, 127] signed byte, originally a -#define P_SignedRandom() ((INT32)P_RandomByte() - 128) // function of its own, moved to a macro +#define M_SignedRandom() ((INT32)M_RandomByte() + INT8_MIN) // [-128, 127] signed byte, originally a +#define P_SignedRandom() ((INT32)P_RandomByte() + INT8_MIN) // function of its own, moved to a macro #define M_RandomChance(p) (M_RandomFixed() < p) // given fixed point probability, p, between 0 (0%) #define P_RandomChance(p) (P_RandomFixed() < p) // and FRACUNIT (100%), returns true p% of the time // Debugging -fixed_t P_RandomPeek(void); +UINT32 P_RandomPeek(void); // Working with the seed for PRNG #ifdef DEBUGRANDOM diff --git a/src/st_stuff.c b/src/st_stuff.c index 36afd84f9..5ed98ff60 100644 --- a/src/st_stuff.c +++ b/src/st_stuff.c @@ -522,12 +522,10 @@ static void ST_drawDebugInfo(void) if (cht_debug & DBG_RNG) // randomizer testing { fixed_t peekres = P_RandomPeek(); - peekres *= 10000; // Change from fixed point - peekres >>= FRACBITS; // to displayable decimal V_DrawRightAlignedString(320, height - 16, V_MONOSPACE, va("Init: %08x", P_GetInitSeed())); V_DrawRightAlignedString(320, height - 8, V_MONOSPACE, va("Seed: %08x", P_GetRandSeed())); - V_DrawRightAlignedString(320, height, V_MONOSPACE, va("== : .%04d", peekres)); + V_DrawRightAlignedString(320, height, V_MONOSPACE, va("== : %08x", peekres)); height -= 32; }