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423 lines
10 KiB
C
423 lines
10 KiB
C
// SONIC ROBO BLAST 2
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//-----------------------------------------------------------------------------
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// Copyright (C) 1993-1996 by id Software, Inc.
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// Copyright (C) 1998-2000 by DooM Legacy Team.
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// Copyright (C) 2012-2016 by Matthew "Kaito Sinclaire" Walsh.
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// Copyright (C) 2022-2023 by tertu marybig.
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// Copyright (C) 1999-2023 by Sonic Team Junior.
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//
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// This program is free software distributed under the
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// terms of the GNU General Public License, version 2.
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// See the 'LICENSE' file for more details.
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//-----------------------------------------------------------------------------
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/// \file m_random.c
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/// \brief RNG for client effects and PRNG for game actions
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#include "doomdef.h"
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#include "doomtype.h"
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#include "i_system.h" // I_GetRandomBytes
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#include "m_random.h"
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#include "m_fixed.h"
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// SFC32 random number generator implementation
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typedef struct rnstate_s {
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UINT32 data[3];
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UINT32 counter;
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} rnstate_t;
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/** Generate a raw uniform random number using a particular state.
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*
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* \param state The RNG state to use.
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* \return A random UINT32.
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*/
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static inline UINT32 RandomState_Get32(rnstate_t *state) {
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UINT32 result, b, c;
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b = state->data[1];
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c = state->data[2];
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result = state->data[0] + b + state->counter++;
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state->data[0] = b ^ (b >> 9);
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state->data[1] = c * 9;
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state->data[2] = ((c << 21) | (c >> 11)) + result;
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return result;
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}
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/** Seed an SFC32 RNG state with up to 96 bits of seed data.
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*
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* \param state The RNG state to seed.
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* \param seeds A pointer to up to 3 UINT32s to use as seed data.
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* \param seed_count The number of seed words.
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*/
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static inline void RandomState_Seed(rnstate_t *state, UINT32 *seeds, size_t seed_count)
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{
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size_t i;
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state->counter = 1;
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for(i = 0; i < 3; i++)
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{
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UINT32 seed_word;
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if(i < seed_count)
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seed_word = seeds[i];
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else
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seed_word = 0;
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// For SFC32, seed data should be stored in the state in reverse order.
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state->data[2-i] = seed_word;
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}
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for(i = 0; i < 16; i++)
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RandomState_Get32(state);
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}
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/** Gets a uniform number in the range [0, limit).
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* Technique is based on a combination of scaling and rejection sampling
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* and is adapted from Daniel Lemire.
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*
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* \note Any UINT32 is a valid argument for limit.
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*
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* \param state The RNG state to use.
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* \param limit The upper limit of the range.
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* \return A UINT32 in the range [0, limit).
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*/
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static inline UINT32 RandomState_GetKey32(rnstate_t *state, const UINT32 limit)
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{
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UINT32 raw_random, scaled_lower_word;
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UINT64 scaled_random;
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// This algorithm won't work correctly if passed a 0.
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if (limit == 0) return 0;
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raw_random = RandomState_Get32(state);
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scaled_random = (UINT64)raw_random * (UINT64)limit;
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/*The high bits of scaled_random now contain the number we want, but it is
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possible, depending on the number we generated and the value of limit,
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that there is bias in the result. The rest of this code is for ensuring
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that does not happen.
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*/
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scaled_lower_word = (UINT32)scaled_random;
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// If we're lucky, we can bail out now and avoid the division
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if (scaled_lower_word < limit)
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{
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// Scale the limit to improve the chance of success.
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// After this, the first result might turn out to be good enough.
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UINT32 scaled_limit;
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// An explanation for this trick: scaled_limit should be
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// (UINT32_MAX+1)%range, but if that was computed directly the result
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// would need to be computed as a UINT64. This trick allows it to be
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// computed using 32-bit arithmetic.
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scaled_limit = (-limit) % limit;
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while (scaled_lower_word < scaled_limit)
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{
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raw_random = RandomState_Get32(state);
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scaled_random = (UINT64)raw_random * (UINT64)limit;
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scaled_lower_word = (UINT32)scaled_random;
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}
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}
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return scaled_random >> 32;
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}
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// The default seed is the hexadecimal digits of pi, though it will be overwritten.
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static rnstate_t m_randomstate = {
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.data = {0x4A3B6035U, 0x99555606U, 0x6F603421U},
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.counter = 16
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};
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// ---------------------------
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// RNG functions (not synched)
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// ---------------------------
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/** Provides a random fixed point number. Distribution is uniform.
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* As with all M_Random functions, not synched in netgames.
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*
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* \return A random fixed point number from [0,1).
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*/
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fixed_t M_RandomFixed(void)
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{
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return RandomState_Get32(&m_randomstate) >> (32-FRACBITS);
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}
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/** Provides a random byte. Distribution is uniform.
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* As with all M_Random functions, not synched in netgames.
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*
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* \return A random integer from [0, 255].
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*/
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UINT8 M_RandomByte(void)
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{
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return RandomState_Get32(&m_randomstate) >> 24;
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}
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/** Provides a random integer for picking random elements from an array.
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* Distribution is uniform.
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* As with all M_Random functions, not synched in netgames.
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*
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* \param a Number of items in array.
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* \return A random integer from [0,a).
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*/
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INT32 M_RandomKey(INT32 a)
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{
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boolean range_is_negative;
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INT64 range;
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INT32 random_result;
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range = a;
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range_is_negative = range < 0;
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if(range_is_negative)
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range = -range;
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random_result = RandomState_GetKey32(&m_randomstate, (UINT32)range);
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if(range_is_negative)
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random_result = -random_result;
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return random_result;
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}
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/** Provides a random integer in a given range.
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* Distribution is uniform.
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* As with all M_Random functions, not synched in netgames.
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*
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* \param a Lower bound.
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* \param b Upper bound.
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* \return A random integer from [a,b].
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*/
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INT32 M_RandomRange(INT32 a, INT32 b)
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{
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if (b < a)
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{
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INT32 temp;
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temp = a;
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a = b;
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b = temp;
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}
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const UINT32 spread = b-a+1;
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return (INT32)((INT64)RandomState_GetKey32(&m_randomstate, spread) + a);
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}
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/** Attempts to seed the unsynched RNG from a good random number source
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* provided by the operating system.
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* \return true on success, false on failure.
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*/
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boolean M_RandomSeedFromOS(void)
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{
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UINT32 complete_word_count;
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union {
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UINT32 words[3];
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char bytes[sizeof(UINT32[3])];
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} seed_data;
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complete_word_count = I_GetRandomBytes((char *)&seed_data.bytes, sizeof(seed_data)) / sizeof(UINT32);
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// If we get even 1 word of seed, it's fine, but any less probably is not fine.
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if (complete_word_count == 0)
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return false;
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RandomState_Seed(&m_randomstate, (UINT32 *)&seed_data.words, complete_word_count);
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return true;
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}
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void M_RandomSeed(UINT32 seed)
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{
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RandomState_Seed(&m_randomstate, &seed, 1);
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}
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// ------------------------
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// PRNG functions (synched)
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// ------------------------
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// Holds the current seed.
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static UINT32 randomseed = 0xBADE4404;
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// Holds the INITIAL seed value. Used for demos, possibly other debugging.
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static UINT32 initialseed = 0xBADE4404;
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/** Provides a random fixed point number.
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* This is a variant of an xorshift PRNG; state fits in a 32 bit integer structure.
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*
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* \return A random fixed point number from [0,1).
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*/
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ATTRINLINE static fixed_t FUNCINLINE __internal_prng__(void)
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{
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randomseed ^= randomseed >> 13;
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randomseed ^= randomseed >> 11;
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randomseed ^= randomseed << 21;
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return ( (randomseed*36548569) >> 4) & (FRACUNIT-1);
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}
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/** Provides a random fixed point number. Distribution is uniform.
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* Literally a wrapper for the internal PRNG function.
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*
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* \return A random fixed point number from [0,1).
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*/
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#ifndef DEBUGRANDOM
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fixed_t P_RandomFixed(void)
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{
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#else
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fixed_t P_RandomFixedD(const char *rfile, INT32 rline)
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{
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CONS_Printf("P_RandomFixed() at: %sp %d\n", rfile, rline);
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#endif
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return __internal_prng__();
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}
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/** Provides a random byte. Distribution is uniform.
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* If you're curious, (&0xFF00) >> 8 gives the same result
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* as a fixed point multiplication by 256.
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*
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* \return Random integer from [0, 255].
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* \sa __internal_prng__
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*/
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#ifndef DEBUGRANDOM
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UINT8 P_RandomByte(void)
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{
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#else
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UINT8 P_RandomByteD(const char *rfile, INT32 rline)
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{
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CONS_Printf("P_RandomByte() at: %sp %d\n", rfile, rline);
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#endif
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return (UINT8)((__internal_prng__()&0xFF00)>>8);
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}
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/** Provides a random integer for picking random elements from an array.
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* Distribution is uniform.
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* NOTE: Maximum range is 65536.
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*
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* \param a Number of items in array.
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* \return A random integer from [0,a).
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* \sa __internal_prng__
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*/
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#ifndef DEBUGRANDOM
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INT32 P_RandomKey(INT32 a)
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{
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#else
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INT32 P_RandomKeyD(const char *rfile, INT32 rline, INT32 a)
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{
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CONS_Printf("P_RandomKey() at: %sp %d\n", rfile, rline);
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#endif
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return (INT32)(((INT64)__internal_prng__() * a) >> FRACBITS);
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}
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/** Provides a random integer in a given range.
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* Distribution is uniform.
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* NOTE: Maximum range is 65536.
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*
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* \param a Lower bound.
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* \param b Upper bound.
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* \return A random integer from [a,b].
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* \sa __internal_prng__
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*/
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#ifndef DEBUGRANDOM
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INT32 P_RandomRange(INT32 a, INT32 b)
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{
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#else
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INT32 P_RandomRangeD(const char *rfile, INT32 rline, INT32 a, INT32 b)
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{
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CONS_Printf("P_RandomRange() at: %sp %d\n", rfile, rline);
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#endif
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return (INT32)(((INT64)__internal_prng__() * (b-a+1)) >> FRACBITS) + a;
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}
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// ----------------------
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// PRNG seeds & debugging
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// ----------------------
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/** Peeks to see what the next result from the PRNG will be.
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* Used for debugging.
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*
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* \return A 'random' fixed point number from [0,1).
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* \sa __internal_prng__
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*/
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fixed_t P_RandomPeek(void)
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{
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UINT32 r = randomseed;
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fixed_t ret = __internal_prng__();
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randomseed = r;
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return ret;
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}
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/** Gets the current random seed. Used by netgame savegames.
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*
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* \return Current random seed.
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* \sa P_SetRandSeed
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*/
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#ifndef DEBUGRANDOM
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UINT32 P_GetRandSeed(void)
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{
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#else
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UINT32 P_GetRandSeedD(const char *rfile, INT32 rline)
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{
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CONS_Printf("P_GetRandSeed() at: %sp %d\n", rfile, rline);
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#endif
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return randomseed;
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}
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/** Gets the initial random seed. Used by demos.
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*
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* \return Initial random seed.
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* \sa P_SetRandSeed
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*/
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#ifndef DEBUGRANDOM
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UINT32 P_GetInitSeed(void)
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{
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#else
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UINT32 P_GetInitSeedD(const char *rfile, INT32 rline)
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{
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CONS_Printf("P_GetInitSeed() at: %sp %d\n", rfile, rline);
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#endif
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return initialseed;
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}
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/** Sets the random seed.
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* Used at the beginning of the game, and also for netgames.
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*
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* \param rindex New random index.
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* \sa P_GetRandSeed
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*/
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#ifndef DEBUGRANDOM
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void P_SetRandSeed(UINT32 seed)
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{
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#else
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void P_SetRandSeedD(const char *rfile, INT32 rline, UINT32 seed)
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{
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CONS_Printf("P_SetRandSeed() at: %sp %d\n", rfile, rline);
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#endif
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// xorshift requires a nonzero seed
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// this should never happen, but just in case it DOES, we check
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if (!seed) seed = 0xBADE4404;
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randomseed = initialseed = seed;
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}
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/** Gets a randomized seed for setting the random seed.
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* This function will never return 0, as the current P_Random implementation
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* cannot handle a zero seed. Any other seed is equally likely.
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*
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* \sa P_GetRandSeed
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*/
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UINT32 M_RandomizedSeed(void)
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{
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UINT32 seed;
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do {
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seed = RandomState_Get32(&m_randomstate);
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} while(seed == 0);
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return seed;
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}
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