[vorbis-dev] mdct.c

[Pattara Kiatisevi]

Hi,

Firstly thank you for the answer.

On Mon, 18 Mar 2002, Monty wrote:

>
> > As we're trying to put libvorbis on LEON chip running on XSV-800 FPGA
> > board, the code runs now (simple player using Pthread on RTEMS/LEON)  but
> > it seems that we have to implement some functions in hardware in order to
> > help speed up the decoding process. We target this mdct_backward()
> > first. Do you have any comment? Is there any other hardware-friendly and
> > computation-intensive functions?
>
> Most other operations are vectorizable...  The LSP filter code (only
> used by re-pc bitstreams) could also benefit from
          ^^^^^	Hmm, what is this re-pc?

There doesn't seem to be the calls vorbis_lsp_to_curve in my player
code so far. Not sure in which situation it will be used.

Ok, from your information then I go for CVS code. I noticed an
option"#define MDCT_INTEGERIZED" in mdct.h so I tried it. Hmm, the sound
output is likely not correct and I checked the result of mdct_backward
compared to the floating point version, they are not really similar(see
below). So this is the work to be done, right? Or I am missing something.

[floating point]
Calling mdct_init functions...
Calling mdct_backward functions...
Output values:
Value at 0x0804BC80 : 44.019447
Value at 0x0804BC84 : -43.652561
Value at 0x0804BC88 : 42.087036
Value at 0x0804BC8C : -41.769104
Value at 0x0804BC90 : 40.410435
Value at 0x0804BC94 : -40.134113
Value at 0x0804BC98 : 38.952457
Value at 0x0804BC9C : -38.712002
Value at 0x0804BCA0 : 37.683647
Value at 0x0804BCA4 : -37.474438
Value at 0x0804BCA8 : 36.580189
Value at 0x0804BCAC : -36.398438
Value at 0x0804BCB0 : 35.622883
Value at 0x0804BCB4 : -35.465591
Value at 0x0804BCB8 : 34.796074
Value at 0x0804BCBC : -34.660736
Value at 0x0804BCC0 : 34.087040
Value at 0x0804BCC4 : -33.971611
Value at 0x0804BCC8 : 33.485340

[intergerized]
Calling mdct_init functions...
Calling mdct_backward functions...
Output values:
Value at 0x0804B360 : 31.000000
Value at 0x0804B364 : -51.000000
Value at 0x0804B368 : 37.000000
Value at 0x0804B36C : -51.000000
Value at 0x0804B370 : 41.000000
Value at 0x0804B374 : -41.000000
Value at 0x0804B378 : 37.000000
Value at 0x0804B37C : -41.000000
Value at 0x0804B380 : 36.000000
Value at 0x0804B384 : -36.000000
Value at 0x0804B388 : 35.000000
Value at 0x0804B38C : -33.000000
Value at 0x0804B390 : 34.000000
Value at 0x0804B394 : -37.000000
Value at 0x0804B398 : 34.000000
Value at 0x0804B39C : -33.000000
Value at 0x0804B3A0 : 36.000000
Value at 0x0804B3A4 : -30.000000
Value at 0x0804B3A8 : 36.000000
Value at 0x0804B3AC : -31.000000

[cut]

I saw you mentioned about multiplication of int and the magic workaround
(as C union or so). Is the code somewhere in CVS? I'm compiling on x86
platform.

Thank you very much,
Pattara

<p>> Secondly, the fixed-point conversion done in the code can't handle the
> range necessary to deal with Vorbis 1.0 files; the range behavior
> hardwired into the implementation was mostly sufficient for beta four,
> but the codebooks and multiplication vectors for 1.0 simply can't fit
> in 32 bits with a fixed point.  32.32 would work, as would a binary
> point that could move within a 32 bit range (ARM cores can give this
> to an only mildly clever implementation for free; this is the approach
> I've taken).
>
> So, in summary, the ivdev code is a fork of Vorbis from a long time
> ago and doesn't reflect the stacks of bugfixes or complete 1.0 feature
> set.  It does not work with any Ogg files produced by an Ogg encoder
> from the past year or so, and it's my humble [but correct] opinion
> that starting over with a fixed point port from current CVS is an
> easier task than bringing ivdev up to date.
>
> Monty
>
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