Thanks,
~V''lion
Bugle4d
Random number between 2 bounds.
Author
Hey.
I''ve found myself needing to get a number between 2 bounds, IE 0 and 1, or 0 and 255.
I know I can do a integer result with rand() and the modulus operator, but I`d really like a floating point solution.
What`s worked for you guys ?
From what I`ve seen of perlin noise its really slow.
Other random formulae I really don`t know of. :-/
I can`t recall ever running across this problem in my various studies.
Oh yeah- ideally its prety fast- its going to be for a particle emitter.
Thanks,
~V''lion
Bugle4d
Thanks,
~V''lion
Bugle4d
#define RANDOM_FLOAT (rand()/RAND_MAX)
#define RandomNumber(a) (RANDOM_FLOAT*a)
#define RandomRange(a,b) (RandomNumber(b-a)+a)
RANDOM_FLOAT will give you a random number between 0 and 1, RandomNumber will give you a random floating point between 0 and a, and RandomRange will give you a random number between a and b.
Hope this helps!
"There are only three types of people in this world: those who can count, and those who can't."
Just3D
Justin Nordin
J Squared Productions
www.jsquaredproductions.com
[edited by - Just3D on July 27, 2002 6:19:49 PM]
[edited by - Just3D on July 27, 2002 6:20:41 PM]
[edited by - Just3D on July 27, 2002 6:22:08 PM]
#define RandomNumber(a) (RANDOM_FLOAT*a)
#define RandomRange(a,b) (RandomNumber(b-a)+a)
RANDOM_FLOAT will give you a random number between 0 and 1, RandomNumber will give you a random floating point between 0 and a, and RandomRange will give you a random number between a and b.
Hope this helps!
"There are only three types of people in this world: those who can count, and those who can't."
Just3D
Justin Nordin
J Squared Productions
www.jsquaredproductions.com
[edited by - Just3D on July 27, 2002 6:19:49 PM]
[edited by - Just3D on July 27, 2002 6:20:41 PM]
[edited by - Just3D on July 27, 2002 6:22:08 PM]
Just3d,
Those macros should probably read as follows:
#define RANDOM_FLOAT ((float)rand()/(float)RAND_MAX)
#define RandomNumber(a) (RANDOM_FLOAT*a)
Those macros should probably read as follows:
#define RANDOM_FLOAT ((float)rand()/(float)RAND_MAX)
#define RandomNumber(a) (RANDOM_FLOAT*a)
What if you want to find a random # that is not completely random? for instance, what if you want the lower #s to occur more often. In essence, how can you generate a random #, n, where the frequency of the a number = 1 / number ^ 2 or somethign similar... is there a way to do this using a funcion for the frequency f(n)?
thanx for the help!
tazzel3d ~ dwiel
thanx for the help!
tazzel3d ~ dwiel
Well, if you square the random number before dividing by RAND_MAX², there should be more small numbers than large numbers.
Cédric
Cédric
My random number generator returns a truly random number between two bounds. Generating biased random numbers would be a bit harder.
quote:Original post by cedricl
Well, if you square the random number before dividing by RAND_MAX², there should be more small numbers than large numbers.
Warning - RAND_MAX squared might roll-over on some implementations. Might want to do the division first and square the result.
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why didn't I think of it to start with!?!?!?! all you hav to do to generate biased random numbers is create a function to pass the random number through... example:
of course this could all be put into one function, but for ease of explantaion, I wrote it as two. In this way, you can bias the number any way you wish as long as the number always stays between the range of 0 and 1.
if anyone else can come up with a way to bias the number or can pick my method apart, please do so!
Tazzel3d ~ dwiel
[edited by - tazzel3d on July 27, 2002 10:27:30 PM]
#define RANDOM_FLOAT ((float)rand()/(float)RAND_MAX)// biases a random # between 0 and 1float BiasNumber(float num){ return num * num;}// scales the biased # between the range of min and maxfloat ScaleNumber(float num, float min, float max){ return min + (max - min) * num;}// to generate the number, execute:float min = 0;float max = 1000;float randomnum = ScaleNumber(BiasNumber(RANDOM_FLOAT, min, max); of course this could all be put into one function, but for ease of explantaion, I wrote it as two. In this way, you can bias the number any way you wish as long as the number always stays between the range of 0 and 1.
if anyone else can come up with a way to bias the number or can pick my method apart, please do so!
Tazzel3d ~ dwiel
[edited by - tazzel3d on July 27, 2002 10:27:30 PM]
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