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Rockbox mail archiveSubject: Re: ROMbox for fm recorders?Re: ROMbox for fm recorders?
From: BlueChip <cs_bluechip_at_webtribe.net>
Date: Thu, 22 Jul 2004 20:54:11 +0100 > > Will I get slapped for mentioning that you can gain about 7K > > by replacing the bigger of the two random number generators? > >Huh? Where should that be hiding? > >Jörg Errr, sorry dude, I don't understand the question. The (mighty and impressive) Marseinne Twister can be replaced with the Linear Congruity algorithm I have implemeted as the bc_rnd() plugin library. FULL docs (explanations, bibliography, etc) on the algorithm I used are included in the zip file on my site. Be warned though, I use a ">>8" at one point (else the numbers are just not random enough ...I like a specific pattern in my random numbers - LOL) Although the cpu supports >>8, I *THINK* the compiler still implements a nasty macro ...but I actually spotted that on a differnt disassemble, and have yet to check the actual bc_rnd library code itself. As such, if you implemented such a scheme, it may be worth doing it in assembler. Because of the >>8, the numbers are only 24bit ...but I questioned how often I would ever want a random number in the range zero...to...more-than-16-million. The Starfield demo (requesting iirc about 200 random numbers per frame) was, in part, written to test the algorithm. Feel free to confirm my results. Someone said a loonngg time ago that it had been rejected due to ack of random'ness, and yes, without the >>8 the sequence is thoroughly unacceptable WRT assembler: If you look at the line() function in the bc_gfx lib, you will see how (thanks to amiconn) I have optimised the abs() function ...essentially, both C and assembler are provided and the 'right' one is compiled. For such tiny bits of code (and maybe bigger), *I* believe that it is acceptable to offer optimised and unoptimised solutions... If another processor comes along - everything is fine, and the coder has the option to add a #ifdef NEW_CPU if he does not like the result C gives him. Hope I covered what you needed to know, BC _______________________________________________ http://cool.haxx.se/mailman/listinfo/rockbox Received on 2004-07-22 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |