[#48] Add Rand API and make StrRandom() use it.

This commit is contained in:
Jordan Bancino 2023-02-16 00:31:13 +00:00
parent fdecac576f
commit 6a593ab8a0
3 changed files with 129 additions and 9 deletions

83
src/Rand.c Normal file
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@ -0,0 +1,83 @@
/*
* 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 <Util.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
/* 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_mutex_t seedLock = PTHREAD_MUTEX_INITIALIZER;
static unsigned int seed = 0;
int tmp;
/* Limit the range to banish all previously biased results */
const int allowed = RAND_MAX - RAND_MAX % max;
size_t i;
pthread_mutex_lock(&seedLock);
if (!seed)
{
/* Generate a seed from the system time, PID, and TID */
seed = UtilServerTs() ^ getpid() ^ (unsigned long) pthread_self();
}
/* Generate {size} random numbers. */
for (i = 0; i < size; i++)
{
/* Most of the time, this will take about 1 loop */
do
{
tmp = rand_r(&seed);
} while (tmp >= allowed);
/* Since a generated number here is never in the biased range,
* we can now safely use modulo. */
buf[i] = tmp % max;
}
pthread_mutex_unlock(&seedLock);
}
/* Generate just 1 random number */
int
RandInt(unsigned int max)
{
int val = 0;
RandIntN(&val, 1, max);
return val;
}

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@ -25,6 +25,7 @@
#include <Memory.h> #include <Memory.h>
#include <Util.h> #include <Util.h>
#include <Rand.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
@ -153,10 +154,9 @@ char *
StrRandom(size_t len) StrRandom(size_t len)
{ {
static const char charset[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; static const char charset[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
static pthread_mutex_t seedLock = PTHREAD_MUTEX_INITIALIZER;
static unsigned int seed = 0;
char *str; char *str;
int * nums;
size_t i; size_t i;
if (!len) if (!len)
@ -165,25 +165,27 @@ StrRandom(size_t len)
} }
str = Malloc(len + 1); str = Malloc(len + 1);
if (!str) if (!str)
{ {
return NULL; return NULL;
} }
pthread_mutex_lock(&seedLock); nums = Malloc(len);
if (!nums)
if (!seed)
{ {
seed = UtilServerTs() ^ getpid() ^ (unsigned long) pthread_self(); Free(str);
return NULL;
} }
/* TODO: This seems slow. */
RandIntN(nums, len, sizeof(charset) - 1);
for (i = 0; i < len; i++) for (i = 0; i < len; i++)
{ {
str[i] = charset[rand_r(&seed) % (sizeof(charset) - 1)]; str[i] = charset[nums[i]];
} }
pthread_mutex_unlock(&seedLock); Free(nums);
str[len] = '\0'; str[len] = '\0';
return str; return str;
} }

35
src/include/Rand.h Normal file
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@ -0,0 +1,35 @@
/*
* 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.
*/
#ifndef TELODENDRIA_RAND_H
#define TELODENDRIA_RAND_H
#include <stddef.h>
extern int
RandInt(unsigned int);
extern void
RandIntN(int *, size_t, unsigned int);
#endif /* TELODENDRIA_RAND_H */