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Subject: Optimized bitswap

Optimized bitswap

From: Magnus Holmgren <>
Date: Sun, 18 Aug 2002 20:54:43 +0200


After testing using a small fliptable (i.e. 256 bytes rather than 128
kB), I've found that the following code in mpeg.c:bitswap() actually is
quick enough (at least when executing in internal RAM) on my Player.
Seems to slow down scrolling a bit though. :)

    data[i] = (fliptable[data[i] >> 8] << 8)
        | fliptable[data[i] & 0xff];

The memory accesses seems to be the critical part. (I first tried
swaping a byte at a time, reading/writing each byte to the MP3 buffer,
but that didn't work well.) Perhaps the above should be rewritten in

Using a tweaked playlist limit (2000 tracks, as I don't need more), I
now have buffer on 1.84 MB. :)

Magnus Holmgren
Received on 2002-08-18

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