Create random integer in range from random double

I get random double number [0,1) from mersenne twister. How would I get random [0,x) from mersenne twister output?

Mersenne twister outputs either random integer in total range or random [0,1)

It is important that it is evenly distributed, so I doubt that basic floor(mersenneRandom()*x) will do.

if it does, then great.