Cytoplasm/src/Rand.c

174 lines
5 KiB
C

/*
* Copyright (C) 2022-2023 Jordan Bancino <@jordan:bancino.net>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <Rand.h>
#include <Int.h>
#include <UInt64.h>
#include <Util.h>
#include <Memory.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#define RAND_STATE_VECTOR_LENGTH 624
#define RAND_STATE_VECTOR_M 397
#define RAND_UPPER_MASK 0x80000000
#define RAND_LOWER_MASK 0x7FFFFFFF
#define RAND_TEMPER_B 0x9D2C5680
#define RAND_TEMPER_C 0xEFC60000
typedef struct RandState
{
UInt32 mt[RAND_STATE_VECTOR_LENGTH];
int index;
} RandState;
static void
RandSeed(RandState * state, UInt32 seed)
{
state->mt[0] = seed & 0xFFFFFFFF;
for (state->index = 1; state->index < RAND_STATE_VECTOR_LENGTH; state->index++)
{
state->mt[state->index] = (6069 * state->mt[state->index - 1]) & 0xFFFFFFFF;
}
}
static UInt32
RandGenerate(RandState * state)
{
static const UInt32 mag[2] = {0x0, 0x9908B0DF};
UInt32 result;
if (state->index >= RAND_STATE_VECTOR_LENGTH || state->index < 0)
{
int kk;
if (state->index >= RAND_STATE_VECTOR_LENGTH + 1 || state->index < 0)
{
RandSeed(state, 4357);
}
for (kk = 0; kk < RAND_STATE_VECTOR_LENGTH - RAND_STATE_VECTOR_M; kk++)
{
result = (state->mt[kk] & RAND_UPPER_MASK) | (state->mt[kk + 1] & RAND_LOWER_MASK);
state->mt[kk] = state->mt[kk + RAND_STATE_VECTOR_M] ^ (result >> 1) ^ mag[result & 0x1];
}
for (; kk < RAND_STATE_VECTOR_LENGTH - 1; kk++)
{
result = (state->mt[kk] & RAND_UPPER_MASK) | (state->mt[kk + 1] & RAND_LOWER_MASK);
state->mt[kk] = state->mt[kk + (RAND_STATE_VECTOR_M - RAND_STATE_VECTOR_LENGTH)] ^ (result >> 1) ^ mag[result & 0x1];
}
result = (state->mt[RAND_STATE_VECTOR_LENGTH - 1] & RAND_UPPER_MASK) | (state->mt[0] & RAND_LOWER_MASK);
state->mt[RAND_STATE_VECTOR_LENGTH - 1] = state->mt[RAND_STATE_VECTOR_M - 1] ^ (result >> 1) ^ mag[result & 0x1];
state->index = 0;
}
result = state->mt[state->index++];
result ^= (result >> 11);
result ^= (result << 7) & RAND_TEMPER_B;
result ^= (result << 15) & RAND_TEMPER_C;
result ^= (result >> 18);
return result;
}
static void
RandDestructor(void *p)
{
Free(p);
}
/* Generate random numbers using rejection sampling. The basic idea is
* to "reroll" if a number happens to be outside the range. However
* this could be extremely inefficient.
*
* Another idea would just be to "reroll" if the generated number ends up
* in the previously "biased" range, and THEN do a modulo.
*
* This would be far more efficient for small values of max, and fixes the
* bias issue. */
/* This algorithm therefore computes N random numbers generally in O(N)
* time, while being less biased. */
void
RandIntN(int *buf, size_t size, unsigned int max)
{
static pthread_key_t stateKey;
static int createdKey = 0;
/* Limit the range to banish all previously biased results */
const int allowed = RAND_MAX - RAND_MAX % max;
RandState *state;
int tmp;
size_t i;
if (!createdKey)
{
pthread_key_create(&stateKey, RandDestructor);
createdKey = 1;
}
state = pthread_getspecific(stateKey);
if (!state)
{
/* Generate a seed from the system time, PID, and TID */
UInt64 ts = UtilServerTs();
UInt32 seed = UInt64Low(ts) ^ getpid() ^ (unsigned long) pthread_self();
state = Malloc(sizeof(RandState));
RandSeed(state, seed);
pthread_setspecific(stateKey, state);
}
/* Generate {size} random numbers. */
for (i = 0; i < size; i++)
{
/* Most of the time, this will take about 1 loop */
do
{
tmp = RandGenerate(state);
} while (tmp > allowed);
buf[i] = tmp % max;
}
}
/* Generate just 1 random number */
int
RandInt(unsigned int max)
{
int val = 0;
RandIntN(&val, 1, max);
return val;
}