Make mt_random always positive

[viion]

How do I make mt_rand always be a positive number?

[ratcateme]

shouldn't it always be positive?

the manual says "returns a pseudo-random value between 0 and mt_getrandmax()" and i doubt that mt_getrandmax() would return a negative value.

otherwise you could specify a range that would produce positive numbers.

 

Scott.

[viion]

Well it seems to be working now, but how do i make it like, I want a specific number of random numbers. Like a 12 digit number, rather than some random numbers being 5 digit long, or some 10 digit long.

[ratcateme]

like i said specify a range like

mt_rand (1*pow(10*12),1*pow(10*13)-1);

untested but i think it should work

 

Scott.

[dadamssg]

mt_rand() uses two parameters..the first being the lowest value it can randomly generate and the second being the highest...so if you always want a positive 12 digit number you would do

 

mt_rand(100000000000,999999999999);

[Mchl]

Are you all aware, that these numbers are above 32bit integer range?

[dadamssg]

yeah i just tried what i said and it definitely didn't work...so heres something i put together that does...maybe not the most efficient but it works nonetheless...

 

$number = abs(mt_rand(100,999));
$ab = abs(mt_rand(100,999));
$bc = abs(mt_rand(100,999));
$cd = abs(mt_rand(100,999));

echo $number.$ab.$bc.$cd;

[ratcateme]

Are you all aware, that these numbers are above 32bit integer range?

im not very up with the play on how PHP handles large numbers but php.net/int suggest numbers outside the 32bit range would be changed to a float that has a 64bit range that supports up to around 14 decimal digits.

 

Scott.

[dadamssg]

yeah...i just thought about that. so then you would just do something like

$number = abs(mt_rand(100,999));
$ab = abs(mt_rand(100,999));
$bc = abs(mt_rand(100,999));
$cd = abs(mt_rand(100,999));

$randomstring = $number.$ab.$bc.$cd;

$randomnumber = int($random);

 

then you have a random positive 12-digit integer....done and done  haha

[dadamssg]

oops meant this haha

 

$number = abs(mt_rand(100,999));
$ab = abs(mt_rand(100,999));
$bc = abs(mt_rand(100,999));
$cd = abs(mt_rand(100,999));

$random_string = $number.$ab.$bc.$cd;

$random_number = intval($number.$ab.$bc.$cd);

echo $random_string;

[ratcateme]

with php you don't even really need to cast it as a int if you just went $random_string + 1 it should work just the same as a normal number defined as $number = 55

 

Scott.

[Yesideez]

I've never had a problem with mt_rand().

 

If you want a random number between 1 and 6 (rolling a di)

$di=mt_rand(1,6);

 

Between 1 and 24 (random hour of the day)

$di=mt_rand(1,24);

 

There's no need to abs() the result as it always returns a positive integer if you only supply positive inputs.

[dadamssg]

yes but he wants a 12-digit number...a number higher than 32-bit apparently...so you would need to shove a bunch together then intval() it to make it a number(64-bit) again...if he wants to do math calcs with it...otherwise, he could just leave it as a string..and you're right about the abs value thing, it is unnecessary

[Mchl]

Except this code will never generate 100000000000 and similar numbers.

 

How about something like this

 

$number = mt_rand(100000,999999) * 1000000 + mt_rand(0,999999);

 

[Yesideez]

Ah!

 

Anything above a 32bit value will result in very incorrect values as numbers start to "wrap around" when outside of the limits. There's probably a set of scripts somewhere for handling larger values - I've seen one with dates outside of the normal range so I can't see why there isn't one for integers.

[dadamssg]

i didn't think about that....but technically, though the chances are TINY, if the first mt_rand() is 999999 and the second is 999999 youd get

 

1,999,997,000,001 thirteen digits

[Mchl]

Of course there is

bcmath

 

 

dadamssg: can't see how 999,999,000,000 + 999,999 gives 1,999,997,000,001

[Yesideez]

Imagine you have an unsigned tinyint - this ranges from 0 to 255. If you add 1 to it you don't get 256 because a tinyint can't be 256 - its upper limit is 255. I think it goes back to 0 - wraps around.

 

Same goes for higher numbers when outside their limits.

[Mchl]

If PHP encounters a number beyond the bounds of the integer  type' date=' it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the integer type will return a float instead. [/quote']

 

The only problem is, mt_rand will always return 2^31-1 when the range is above 2^31.