Re: Help with some clever bit operations

On Tue, 2006-06-13 at 11:03, Jochem Maas wrote: > Robert Cummings wrote: > > On Tue, 2006-06-13 at 06:22, Jochem Maas wrote: > >> My brain needs a crutch when trying doing this kind of thing > >> (normally I only write hex number literally when dealing with bitwise stuff - > >> the conversion stuff still makes my head spin) - this is what this table is for: > >> > >> 128 64 32 16 8 4 2 1 > >> 1 0 1 1 0 1 0 1 > >> 0 1 0 1 1 1 0 0 > >> 0 0 0 0 1 1 1 1 > >> > >> and then I did this - hopefully it shows what you can/have to do: > >> > >> <?php > >> > >> // set some values > >> $oldval = 128 + 32 + 16 + 4 + 1; // 10110101 > >> $update = 64 + 16 + 8 + 4; // 01011100 > >> $mask = 8 + 4 + 2 + 1; // 00001111 > > > > You could just do the following: > > > > $oldval = bindec( '10110101' ); > > $update = bindec( '01011100' ); > > $mask = bindec( '00001111' ); > > when I was writing the reply I played with about 5 different > conversion funcs - pretty everything expect bindec() !!! > > I guess i was being lazy - but then I alway think directly in hex numbers > when doing bitwise stuff (at least I use hex notation for the constant value > that I almost invariably end up creating) > > anyway cheers for the lightbuld moment :-) Well yours is at least faster since there's no function calls. Though one can also do the following to avoid memorizing decimal bit values :) $oldval = (1 << 7) + (1 << 5) + (1 << 4) + (1 << 2) + (1 << 0); $update = (1 << 6) + (1 << 4) + (1 << 3) + (1 << 2); $mask = (1 << 3) + (1 << 2) + (1 << 1) + (1 << 0); :) Cheers, Rob. -- .------------------------------------------------------------. | InterJinn Application Framework - http://www.interjinn.com | :------------------------------------------------------------: | An application and templating framework for PHP. Boasting | | a powerful, scalable system for accessing system services | | such as forms, properties, sessions, and caches. InterJinn | | also provides an extremely flexible architecture for | | creating re-usable components quickly and easily. | `------------------------------------------------------------'