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Subject: Re: Optimized bitswap
From: Linus Nielsen Feltzing (
Date: 2002-08-18

On Sun, 18 Aug 2002 22:10:37 +0200, Magnus Holmgren wrote:
> How much?

Player: 12MHz, Recorder: 11.0592MHz

> Yes, playback is fine. No other problems noticed (but I haven't
> tested *that* much yet).

It shows best when playing high-bitrate songs, since the bitswap
pretty much determines the watermark level.

> And maybe word fetches are faster than byte fetches? E.g., aren't
> there architectures that always fetches e.g. longs, even for byte
> accesses?

All accesses take the same time, bytes, words, longwords. However,
your loop would probably (if GCC delivers) read a word of MP3 data
and keep it in a register for the two table lookups. I based my
"calculations" on that assumption.

> Are there any L1 caches that could keep (much of) the table in
> memory?

No caches, unfortunately.


Linus Nielsen Feltzing, on 2002-08-18

Page was last modified "Jan 10 2012" The Rockbox Crew