Speex dev - Sep 2005 - Precomputing the remaining floating point operations.

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

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 ? 17:34 +0200, Nic Roets a ?crit
:
> 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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