> Just occurred to me a brilliant way to grab random values,
You sound like a noob who just "discovered" bubble sorting and thinks it's the most awesome thing they've ever seen.
> I've tested a few times just now and it seems to be a usable option even for security, at least to me anyways:
I wouldn't use this for a student dice rolling program, never mind for any serious statistical or security application.
The algorithm (such as it is), is painfully slow as well as being singularly useless.
Diehard tests - Wikipedia
On my machine, malloc() returns the same pointer every time, and time() is a constant.
clock() is barely able to do any better than being an incrementing counter.
Code:
#include<stdio.h>
#include<time.h>
#include<stdlib.h>
#include<stddef.h>
#include<limits.h>
typedef ptrdiff_t mcc_rnd_t;
long mcc_rnd( mcc_rnd_t *seed, long min, long max ) {
unsigned char *tmp = malloc(1);
/* Initial random value */
long val = time(NULL) + ((ptrdiff_t)tmp);
if ( !seed ) seed = (mcc_rnd_t*)(&seed);
if ( *seed == 0 ) *seed = 1;
val %= *seed;
val *= clock();
free(tmp);
*seed <<= 1;
return (val > max) ? max : (val < min ? min : val);
}
void t1() {
printf("100 Clocks()\n");
long tests[100];
for ( int i = 0; i < 100; ++i ) {
tests[i] = clock();
}
for ( int i = 0; i < 100; ++i ) {
(void)printf( "%ld\n", tests[i] );
}
}
void t2() {
printf("100 times()\n");
long tests[100];
for ( int i = 0; i < 100; ++i ) {
tests[i] = time(NULL);
}
for ( int i = 0; i < 100; ++i ) {
(void)printf( "%ld\n", tests[i] );
}
}
void t3() {
printf("100 pointers()\n");
void *tests[100];
for ( int i = 0; i < 100; ++i ) {
tests[i] = malloc(1);
free(tests[i]);
}
for ( int i = 0; i < 100; ++i ) {
(void)printf( "%p\n", tests[i] );
}
}
int main() {
int i;
long seed = 1;
long tests[100];
t1();
t2();
t3();
for ( i = 0; i < 100; ++i ) {
tests[i] = mcc_rnd( &seed, LONG_MIN,LONG_MAX);
}
for ( i = 0; i < 100; ++i ) {
(void)printf( "%ld\n", tests[i] );
}
int dice[6] = { 0 };
for ( int i = 0 ; i < 60000000 ; i++ ) {
int d = mcc_rnd( &seed, LONG_MIN,LONG_MAX) % 6;
dice[d]++;
}
for ( int i = 0 ; i < 6 ; i++ ) {
printf("%d: %d\n", i, dice[i]);
}
}
Your 'distribution' is awful. Your online casino operator is now suing you.
Code:
0: 25929392
1: 3481475
2: 9589231
3: 7932192
4: 9587561
5: 3480149
real 0m21.880s
user 0m7.460s
sys 0m14.416s
Compare with calling rand() millions of times.
Much better, and MUCH quicker!.
Code:
0: 9998142
1: 9999581
2: 10000326
3: 10003300
4: 9997641
5: 10001010
real 0m0.600s
user 0m0.596s
sys 0m0.000s
Originally Posted by Bjarne Stroustrup (2000-10-14)
also the seed is an option, actually runs better without (when NULL is given), I've already tested this myself and advise you to test it also before you post again, (I did multiple runs just to see if the numbers where consistent or not)
