[Speex-dev] Precomputing the remaining floating point operations.

[Jean-Marc Valin]

Hi Nic,

While I must say it's a clever idea to cache data, I think merging this
would be a really bad idea. The possibilities for screwing things up
with this are just too great - there's already people sending all kind
of crap to the encoder (and expecting it to work) that I don't want to
introduce something that's really more complicated to understand. I
think the initialization code should just be fixed-point-ized at some
pint. BTW, since initialization is only run once for a channel (and
running for more channels will break your hack), even float emulation
will usually work fine in the mean time.

As for accuracy in converting to fixed-point, I don't think it's a big
issue. The two things that are still in float are the window, for which
I already have a fixed-point version of cos, and the auto-correlation
lag-window, which can probably be approximated very well by Taylor
expansion.

	Jean-Marc

Le lundi 26 septembre 2005 à 17:34 +0200, Nic Roets a écrit :
> I see there are still some floating point operations left in the codec 
> init(ialization) code. Changing that code to fixed point is not only 
> difficult (due to the trigonometric functions etc) but may also degrade the 
> precision.
> 
> Here is an idea whereby we can easily precompute (record) all those values 
> on a powerful processor and then use (replay) them on an embedded processor 
> / DSP. The only requirement is that 'xxx_init_xxx' should be called in 
> exactly the same environment in both cases (e.g. FIXED_POINT and with the 
> same mode or sequence of modes).
> 
> All that's needed is to include the code segment below in one of the .h 
> files and wrap all those float calculations in RECOPLAY, e.g. int sqrt2 = 
> RECOPLAY(sqrt(2)*16384)
> I've also made RECOPLAY_MARK(name) to synchronize the process.
> 
> #ifdef RECORD
> #include <stdio.h>
> 
> extern FILE *recordFile;
> 
> #define _RECOPLAY_FOPEN \
>     if (!recordFile && (recordFile = fopen ("precompute.c", "w")) != NULL) 
> { \
>       fprintf (recordFile, "#include \"config.h\"\n\
>       #ifndef EMBEDDED\n\
>       #include <stdio.h>\n\
>       FILE *recordFile = NULL;\n\
>       #else\n\
>       int recordDefault[]={\n");\
>       atexit (CloseRecordFile); \
>     } \
> 
> #define RECOPLAY_MARK(name) { _RECOPLAY_FOPEN; \
>     if (recordFile) fprintf (recordFile, "}, record"#name"[] = {\n"); \
>   }
> 
> #define RECOPLAY(x) ({ \
>     int v = (x); \
>     _RECOPLAY_FOPEN; \
>     fprintf (recordFile, "  %d,\n", v); \
>     v; \
>   })
> 
> static void CloseRecordFile (void)
> {
>   if (recordFile) {
>     fprintf (recordFile, "}, *recordPtr = recordDefault;\n      #endif\n");
>     fclose (recordFile);
>   }
> }
> 
> #else /* Not recording */
> #ifndef EMBEDDED
> #define RECOPLAY_MARK(x)
> #define RECOPLAY(x) (x)
> #else
> extern int *recordPtr;
> #define RECOPLAY_MARK(x) {extern int record ## x[]; recordPtr = record ## 
> x; }
> #define RECOPLAY(x) *recordPtr++
> /* Embedded version of RECOPLAY does not evaluate 'x' */
> #endif
> #endif
> 
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