
Rockbox mail archiveSubject: Re: Math in RockboxRe: Math in Rockbox
From: BlueChip <cs_bluechip_at_webtribe.net>
Date: Wed, 06 Jul 2005 19:52:05 +0100 what values of 'x' ? all positive? include 0? if (x<0) return(0); // cannot handle negative values of x if (x>9) return(1); // result will be > (2^32)1 unsigned long r = 1; while (x>0) r = (r<<4)+(r<<1); // r*8 + r*2 return (r); given you only have 9 possible return values, a lookup table would be faster and not THAT much more cost in codespace. At 16:53 06/07/2005, you wrote: >well... If I just think of a q&d solution: > >long exp10(int x) { > long result = 10; > while (x) { > result = result * 10; > } > return result; >} > >I haven't tested this, but it can be something like this. (And I'm sure >it's slow as hell for large values of x) > >Tomas > >lear_at_algonet.se wrote: > > >Hi, > > > >For an upcoming patch, I need some fixed or floatingpoint math. Does > anyone have > >a good fixedpoint implementation of pow(10, x) (or exp10(x)), or some > hints > >on how to implement it? It doesn't need to be particularly fast; small size > >is to be preferred actually. > > > >Or would it be acceptable to bring in the compiler's floating point > stuff for > >this? The idea is to not put it in a plugin or a codec (though I could put > >it in the codec lib, it isn't really the natural place for it :)... > > > > Magnus > > > >_______________________________________________ > >http://cool.haxx.se/mailman/listinfo/rockbox > > > > > >_______________________________________________ >http://cool.haxx.se/mailman/listinfo/rockbox _______________________________________________ http://cool.haxx.se/mailman/listinfo/rockbox Received on 20050706 Page template was last modified "Mon Jun 14 16:30:06 2021" The Rockbox Crew  Privacy Policy 