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Author Topic: Randomizer  (Read 2964 times)

Grincheux

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Randomizer
« on: March 24, 2021, 03:55:35 PM »
I would like to generate random numbers between two limits.
It is easy to generate numbers between 0..N
but my problem is to have random numbers between -361 and +361

I have written this but I am not satisfied:
Code: [Select]
_iResult = MAX_EDIT_FIELDS - rand() % ((2 * MAX_EDIT_FIELDS) + 1);
I create a number between 0 and 722 then I substract 361.

Who could help me?
« Last Edit: March 24, 2021, 03:57:35 PM by Grincheux »

Offline John Z

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Re: Randomizer
« Reply #1 on: March 24, 2021, 05:03:44 PM »
Well I'll give it a try how about this:
Code: [Select]
RAND_MAX = MAX_EDIT_FIELDS;
srand(_rdtsc());                                   // seed it
_iResult  = (rand() > (RAND_MAX/2) ? rand() :rand() * -1); // +/- 0 to MAX_EDIT_FIELDS

John Z

Grincheux

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Re: Randomizer
« Reply #2 on: March 24, 2021, 06:18:45 PM »
ok I will test.
Thak You :o

Offline MrBcx

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Re: Randomizer
« Reply #3 on: March 24, 2021, 10:34:17 PM »
Here's another way ... 
 

int rnd2 (int _lower, int _upper)
 {
   return fmod(rand(),((_upper - _lower+1))) + _lower;
 }
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Grincheux

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Re: Randomizer
« Reply #4 on: March 24, 2021, 11:49:13 PM »
Code: [Select]
fmod(rand(),((MAX_EDIT_FIELDS - -MAX_EDIT_FIELDS+1))) + -MAX_EDIT_FIELDS;Does not work
Code: [Select]
_iResult  = (rand() > (RAND_MAX/2) ? rand() :rand() * -1); // +/- 0 to MAX_EDIT_FIELDSGives too big numbers
Code: [Select]
_iResult = MAX_EDIT_FIELDS - rand() % ((2 * MAX_EDIT_FIELDS) + 1);Give the best results

Thanks to everyone

Offline John Z

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Re: Randomizer
« Reply #5 on: March 25, 2021, 12:33:21 AM »
Hmmmm ... the number can’t be bigger than what RAND_MAX is set to.
I’ll double check.

John Z

Well darn! #undef RAND_MAX, then #define RAND_MAX 0x169 but rand() is ignoring
RAND_MAX.

From book on C
“The function rand() can be used to generate a pseudo-random integer value between 0 and RAND_MAX (0 and RAND_MAX included).”

My sincere apologies for my garbage ‘solution’! A good lesson for me.

John Z
« Last Edit: March 25, 2021, 01:54:35 AM by John Z »

Offline frankie

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Re: Randomizer
« Reply #6 on: March 25, 2021, 12:29:46 PM »
Well darn! #undef RAND_MAX, then #define RAND_MAX 0x169 but rand() is ignoring
RAND_MAX.

From book on C
“The function rand() can be used to generate a pseudo-random integer value between 0 and RAND_MAX (0 and RAND_MAX included).”
The symbol RAND_MAX defines the max value that the function 'rand()' can output, isn't a parameter to change to obtain a user range, the max value is compiled in the library function 'rand()' and can't change.
Once again users must not change the system definitions.
It is better to be hated for what you are than to be loved for what you are not. - Andre Gide

Grincheux

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Re: Randomizer
« Reply #7 on: March 25, 2021, 12:46:52 PM »
RAND_MAX is equal to 32768 if I have well understood what I read.
In fact it is not possible to create negative numbers.
Funcio ALEA.BETWEEN.xxx in OpenOffice

Offline John Z

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Re: Randomizer
« Reply #8 on: March 25, 2021, 03:00:47 PM »
Always learn from ones mistakes.  so revised to be below , but I'm not saying it is better than yours
just different.

MAX_EDIT_FIELDS = 361;
srand(_rdtsc());
_iResult  = (rand() > (RAND_MAX/2) ? (rand() % MAX_EDIT_FIELDS) : -1*(rand() % MAX_EDIT_FIELDS);
corrected typo:
_iResult  = (rand() > (RAND_MAX/2) ? (rand() % MAX_EDIT_FIELDS): -1*(rand() % MAX_EDIT_FIELDS));
----------------
output
-59, -90, 27, -123, 104, -187, 306, 102, 257, -345, 13, -349, -134, 181, 238, -8, 154, -30, 99, -170, 163, -171, 91, 331, -25, 201, 121, -66, 320, 33, -118, -108, -146, -6, 129, 210, 128, 129, -125, -222, 235, -273, 113, -99, -15, 36, 282, -50, 163, -284, -37, -148, -8, 143, 329, -44, -267, 235, -91, 215, 17, 308, -18, 22, -49, -88, -326, -126, 112, -174, 244, -65, 318, 104, 315, -267, -89, 252, -31, -2, -86, -189, -302, 110, 260, 296, 274, -64, 57, -43, 279, 308, -283, 161, -274, -166, -53, 136, -29, -1, -285, 78, 316, 49, -64, 300, 297, 232, -85, -20, -275, 18, 107, -132, 268, 81, 71, -42, -72, 87, 198, -226, -187, 24, 167, 69, 209, -84, -214, 256, -179, 255, -287, -165, 28, -331, 2, -293, -177, 272, -170, 312, 119, -218, 110, 355, 205, -75, -176, 344, -159, -32, -274, 283, 325, -6, -229, -42, -227, -8, -358, 245, -101, 353, 307, -190, -293, -131, -341, -315, 0, 150, 12, -215, -3, -319, 203, -14, 225, 147, 107, -118, 253, 314, -10, -321, -3, 247, -1, 321, 311, 43, 349, 54, -342, 358, 204, 100, 1

John Z
« Last Edit: March 25, 2021, 04:14:41 PM by John Z »

Offline frankie

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Re: Randomizer
« Reply #9 on: March 25, 2021, 03:55:22 PM »
rand() returns an integer between 0 and RAND_MAX. The last is maximum value for each implementation (compiler+libraries set).
To obtain what you want with a gaussian distribution you have to use the rand() output adapted to the required range.
In the following snippet the function myrandom(min, max) returns a number inside the range specified by min and max value.
Code: [Select]
#include <stdio.h>
#include <stdlib.h>

#define MIN -361
#define MAX  361

int myrandom(long long int min, long long int max)
{
return (int)(((long long int)rand() / ((long long int)RAND_MAX / (max - min))) + min);
}

int main(int argc, char *argv[])
{
printf ("Sample randomic -361 <==> +361.\n");

for(;;)
{
int r = myrandom(MIN, MAX);
printf("==> %d%s\n", r, ((r<MIN) || (r>MAX)) ? " ==>Error! out of limit!" : "");
}

return 0;
}
It is better to be hated for what you are than to be loved for what you are not. - Andre Gide

Grincheux

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Re: Randomizer
« Reply #10 on: March 25, 2021, 03:59:49 PM »
The correct syntax is



srand(_rdtsc());
_iResult  = (rand() > (RAND_MAX/2)) ? (rand() % MAX_EDIT_FIELDS) : -1*(rand() % MAX_EDIT_FIELDS);
                                                   /|\
-----------------------------------------


When looping on 361 values, I have many values that are the same



         GetLocalTime(&_St) ;
         srand(_rdtsc()*_St.wMilliseconds) ;


         _iResult = MAX_EDIT_FIELDS - rand() % ((2 * MAX_EDIT_FIELDS) + 1);


//srand(_rdtsc());
//_iResult  = (rand() > (RAND_MAX/2)) ? (rand() % MAX_EDIT_FIELDS) : -1*(rand() % MAX_EDIT_FIELDS);


I have the same problem but there are fewer collisions.
I think that your problem is that you call many times RAND()


Thank You for your help John

Grincheux

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Re: Randomizer
« Reply #11 on: March 25, 2021, 04:13:48 PM »

Frankie, I seems there is no collision !
return (int)(((long long int)rand() / ((long long int)RAND_MAX / (max - min))) + min);


return (int)(((long long int)rand() / ((long long int)RAND_MAX / (361 - -361))) + -361);
return (int)(((long long int)rand() / ((long long int)RAND_MAX / (361 + 361))) - 361);
return (int)(((long long int)rand() / ((long long int)RAND_MAX / 722)) - 361);


YOU ARE THE BEST

Offline frankie

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Re: Randomizer
« Reply #12 on: March 25, 2021, 04:44:41 PM »
Frankie, I seems there is no collision !

Good to hear.
The picture resembles me enough...
It is better to be hated for what you are than to be loved for what you are not. - Andre Gide