Random value in objective c gives incorrect numbers

Question

I need to get random float values in range [-1, 1].

    CGFloat max = 1;
    CGFloat min = -1;

I use following code:

((float)arc4random()/RAND_MAX)*(max-min)+min

But i get value between -1.007 to 2.879 and so on. Where i have a problem. Thank you.

Answer 1

RAND_MAX is not the maximum value of arc4random(). arc4random() returns numbers over the whole range of u_int32_t (0 to (2^32)-1), which is a larger range than rand().

Also, float is not big enough to hold all values in that range to full precision.

Try:

((double)arc4random() / UINT32_MAX) * (max - min) + min