Thanks Stef. It Seems to be what I am looking for. Abdelghani
-------------------------------------------- En date de : Jeu 19.11.15, stepharo <steph...@free.fr> a écrit : Objet: Re: [Pharo-users] BitField À: "abdelghani ALIDRA" <alidran...@yahoo.fr>, "Any question about pharo is welcome" <pharo-users@lists.pharo.org> Date: Jeudi 19 novembre 2015, 20h57 Have a look at the chapter on number in deep into pharo. You get some illustrations of bit operations for numbers bitShift: bitAnd: ... Stef Le 16/11/15 21:16, abdelghani ALIDRA a écrit : Hi everybody, I was discussing with Thibault about the performance of some methods defined on sets ( actually quite slow for big collections, mainly union: and intersection: ) and we were wondering if there is any implementation of some BitField-like class to speed up these operations? May be in an external project? Abdelghani