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This could be just what I need to make Tremor run fast enough on the
AT91SAM7S (ARM7TDMI 55MHz) to decode an average Ogg file. At the moment
I have to over-clock it slightly.<br>
<br>
It looks like you added some tables. I assume this means the code will
grow by a few KB? Not a problem for me as the RAM is far more precious
than the flash memory.<br>
<br>
I'm not actively working on the Ogg Vorbis decoder project at the
moment but I would like to see this make it into the Tremor main branch
so that I can take advantage of it when I get back to it.<br>
<br>
I agree that _LOW_ACCURACY_ mode might as well go away if this new code
is faster with full accuracy.<br>
<br>
<br>
Thanks!<br>
<br>
Nicholas<br>
<br>
<br>
<br>
Mike Giacomelli wrote:
<blockquote cite="mid:SNT119-W13E05063AE1C5D75F2A5EEC12F0@phx.gbl"
type="cite">
<style><!--
.hmmessage P
{
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body.hmmessage
{
font-size: 10pt;
font-family:Verdana
}
--></style>Hi.
<div><br>
</div>
<div><br>
</div>
<div>Over at rockbox.org, we have written a fixed point MDCT for our
embedded targets that is faster then any we have so far come across
(Tremor, libfaad, ffmpeg pre 2008). We have used it with libtremor and
found it to be ~40% faster then stock libtremor mdct on ARM7TDMI and
generally about 30%+ faster on ARM9/ARM11. It is also faster on
Coldfire CPUs and we think there is still room for more improvement. </div>
<div><br>
</div>
<div><br>
</div>
<div>The speed up comes mainly from using a split radix fft that
significantly reduces the number of add/mul operations required.
Additionally, we have provided some ASM segments to improve
performance further. However, even without ASM, we are still
significantly faster then stock Tremor. Some information:</div>
<div><br>
</div>
<div><br>
</div>
<div><a moz-do-not-send="true"
href="http://www.rockbox.org/wiki/FasterMDCT">http://www.rockbox.org/wiki/FasterMDCT</a></div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>We have licensed it under BSD and would like to see it used in
libtremor.</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>One concern I have though is the <span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;">_LOW_ACCURACY_<span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;"> mode
in Tremor. This seems to allow 32 bit only multiplies for targets with
no hardware 32x32->64 bit instruction. We do not support this in
our new MDCT because we are faster in full accuracy mode then current
SVN in low accuracy mode on ARM.</span></span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;"><span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;"><br>
</span></span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;"><span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;"><br>
</span></span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;"><span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;">Is
this a problem? I am of the opinion that it is not (in Tremor-main at
least) as it has minimal advantage on arm/coldfire/x86 which constitute
nearly all FOSS and commercial users of Tremor's main branch. It also
seems to confuse some hardware vendors who have used it on high end ARM
cores that do not benefit significantly from it. </span></span></div>
<div><br>
</div>
<div><br>
</div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;"><span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;">Thanks,</span></span></div>
<div><span class="Apple-style-span"
style="font-family: monospace; font-size: 16px;"><span
class="Apple-style-span"
style="font-family: Verdana; white-space: normal; font-size: 13px;">Mike</span></span></div>
<br>
<hr>The New Busy is not the old busy. Search, chat and e-mail from
your inbox. <a moz-do-not-send="true"
href="http://www.windowslive.com/campaign/thenewbusy?ocid=PID27925::T:WLMTAGL:ON:WL:en-US:WM_HMP:032010_3"
target="_new">Get started.</a>
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