[gst-devel] float caps, category, audioconvert changes

[Benjamin Otte]

On 20 Jul 2003, Ronald Bultje wrote:

> On Sun, 2003-07-20 at 02:34, David Schleef wrote:
> > On Sat, Jul 19, 2003 at 07:53:41PM -0400, Leif Johnson wrote:
> > > I'm still working on fully integrating float audio into the audioconvert
> > > plugin. If anyone has a quick macro to change the endianness of a float or
> > > double, I could use one. :) I'll check in my float changes as soon as they
> > > work for me, but the int side of things should hopefully still work.
> > GUINT32_TO_LE() and GUINT64_TO_LE().
>
> Do UINT functions work for FLOAT types, too? As far as I understand, it
> will just cast it to a guint64 and return it as such, too.
>
It does the byteswapping when needed. But it's an ugly hack to include
somewhere, so we should probably do 2 things:
1) Add GST_FLOAT/DOUBLE_TO_LE/BE somewhere and document why we use that
ugly hack there.
2) File a bug against glib to make them include those macros in future
versions. (done, it's #117901)

> [rbultje at shrek tmp]$ grep GUINT64_TO_LE glibconfig.h
> #define GUINT64_TO_LE(val)      ((guint64) (val))
> [rbultje at shrek tmp]$
>
glibconfig.h is a generated file depending on arch.
On my iBook it looks like this:
#define GUINT64_TO_LE(val)	(GUINT64_SWAP_LE_BE (val))

> http://www.starlink.rl.ac.uk/star/docs/sc13.htx/N-a2b3c2.html has some
> info on float representations (though nothing about doubles :(), and it
> seems the byteorder layout is the same as for ints (that's in the first
> part). From what I understand, an endianness conversion thing could look
> like this (similar to ints):
>
> #ifdef (BYTE_ORDER == G_LITTLE_ENDIAN)
> #define GFLOAT_FROM_LE(x) ((gfloat)(x))
> #define GFLOAT_TO_LE(x) (GFLOAT_FROM_LE(x))
> #define GFLOAT_FROM_BE(x) (gfloat_byteswap(x))
> #define GFLOAT_TO_BE(x) (GFLOAT_FROM_BE(x))
> #else
> #define GFLOAT_FROM_LE(x) (gfloat_byteswap(x))
> #define GFLOAT_TO_LE(x) (GFLOAT_FROM_LE(x))
> #define GFLOAT_FROM_BE(x) ((gfloat)(x))
> #define GFLOAT_TO_BE(x) (GFLOAT_FROM_BE(x))
> #endif
>
> byteswap:
>
> static inline gfloat
> gfloat_byteswap (gfloat in)
> {
>   guint32 bytes = * (guint32 *) ∈
> #ifdef (BYTE_ORDER == G_BIG_ENDIAN)
>   bytes = GUINT32_FROM_LE(bytes);
> #else
>   bytes = GUINT32_FROM_BE(bytes);
> #endif
>   return * (gfloat *) &bytes;
> }
>
> Or so. The double would look the same, but 64 bit:
>
> #ifdef (BYTE_ORDER == G_LITTLE_ENDIAN)
> #define GDOUBLE_FROM_LE(x) ((gdouble)(x))
> #define GDOUBLE_TO_LE(x) (GDOUBLE_FROM_LE(x))
> #define GDOUBLE_FROM_BE(x) (gdouble_byteswap(x))
> #define GDOUBLE_TO_BE(x) (GDOUBLE_FROM_BE(x))
> #else
> #define GDOUBLE_FROM_LE(x) (gdouble_byteswap(x))
> #define GDOUBLE_TO_LE(x) (GDOUBLE_FROM_LE(x))
> #define GDOUBLE_FROM_BE(x) ((gdouble)(x))
> #define GDOUBLE_TO_BE(x) (GDOUBLE_FROM_BE(x))
> #endif
>
> static inline gdouble
> gdouble_byteswap (gdouble in)
> {
>   guint64 bytes = * (guint64 *) ∈
> #ifdef (BYTE_ORDER == G_BIG_ENDIAN)
>   bytes = GUINT64_FROM_LE(bytes);
> #else
>   bytes = GUINT64_FROM_BE(bytes);
> #endif
>   return * (gdouble *) &bytes;
> }
>
> Could you test these in a row (i.e. start with your own endianness, go
> to the other and go back) and see if the data still works? If so, you
> could try to make a file and let people with the "other" endianness read
> it and see if it works for them. If so, we've got a winner.
>
> In all the above, I'm assuming that byte order is the only issue here,
> and that the order of mantissa, sign etc. doesn't change (as the IEEE
> seems to prescribe). I'm not sure of this at all, since I've never known
> a single thing about floats. ;).
>
I can test anything you come up with.

Benjamin

> Ronald
>
> --
> Ronald Bultje <rbultje at ronald.bitfreak.net>
>
>
>
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