Re: [iiwusynth-devel] Bugs / optimization

[Peter Hanappe]

M. Nentwig wrote:

> > you can't use SSE to calculate the sum of four floats at once as in
> > sum(a0,a1,a2,a3).
>
> Yes, I think you are right. Do you know how expensive an addition is,
> compared to a multiplication? If it is about the same, we could process
> four samples at a time and then do the respective additions in parallel
> afterwards. Will require some comments, though :(

We could split the dsp loop into two parts, the length of the first part is a
multiple of four so we can calculate four samples at once, the second part is
the remainder (0 to 3 samples).

> I have a suspicion, that calculating the phase is another minor
> bottleneck. Maybe there are still some folks with old hardware out
> there, but I'm tempted to use a 'long long' integer instead.

I did a quick test with 64 bits integers the other day but somehow messed up.
I think it would be good indeed. The current implementation was already a
fair speedup compare to using double float for the phase.

The current definition for the phase I use locally is:

typedef union {
  struct {
    sint32 index;
    uint32 fract;
  } s;
  sint64 ll;
} iiwu_phase_t;

What I'd like to obtain is that we can use index and fract to get the
integer and fractional part (no bit shifting or masking) and use
the long long for phase increments. Machines without long longs
can still use the old macros.

In my code, I've also added a file, iiwu_types.h, that defines the integer
types. I've copy/pasted part of it below. I can commit it to CVS right
away I've you'd like to use it.

Cheers,
Peter

-----------------------------------------------------------------------


/** Real type */
typedef float iiwu_real_t;


/** Integer types  */

#if defined(_WIN32)

/* Windows */
typedef signed __int8     sint8;
typedef unsigned __int8   uint8;
typedef signed __int16    sint16;
typedef unsigned __int16  uint16;
typedef signed __int32    sint32;
typedef unsigned __int32  uint32;
typedef signed __int64    sint64;
typedef unsigned __int64  uint64;

#elif defined(MACINTOSH)

/* Macintosh */
typedef signed char       sint8;
typedef unsigned char     uint8;
typedef signed short      sint16;
typedef unsigned short    uint16;
typedef signed int        sint32;
typedef unsigned int      uint32;

#error FIXME: define 64 bits types for macintosh (ppc)
typedef int64_t           sint64;
typedef u_int64_t         uint64;

#else

/* Linux */
typedef int8_t            sint8;
typedef u_int8_t          uint8;
typedef int16_t           sint16;
typedef u_int16_t         uint16;
typedef int32_t           sint32;
typedef u_int32_t         uint32;
typedef int64_t           sint64;
typedef u_int64_t         uint64;

#endif

-----------------------------------------------------------------------
> Cheers
>
> Markus
>
>
>
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