Re: Datahandle State API changes

[Stefan Westerfeld <stefan space twc de>]

   Hi!

On Mon, Nov 27, 2006 at 06:35:51PM +0100, Tim Janik wrote:
> >>>+ * Often the state is symmetric, so that the number of output samples
> >>>affected
> >>>+ * before and after the "corresponding" output sample is the same. Then
> >>>the
> >>>+ * function returns this number. If the state is asymmetric, this 
> >>>function
> >>>+ * shall return the maximum of the two numbers.
> >>>+ *
> >>>+ * If multiple data handles are cascaded (for instance when resampling a
> >>
> >>hm, "cascaded"? i'd rather say "nested" (or "chained") here.
> >
> >Ok: I'll use cascaded.
> 
> i don't think "cascaded" is accurate here. cascaded handles could mean
> using handles in parallel (e.g. you could line up 6 handles in a 
> specifically
> ordered cascade to produce a 5.1 dolby handle ;)
> only "nested" and to some extend "chained" carry across the sequential
> ordering of the handles.

Well, "nested" then (it was in the nek patch alteady, just the remark in
md mail was wrong). Btw. your mono -> 5.1 transform will have to
implement get_state, too.

> >>>Index: bse/bsedatahandle-resample.cc
> >>>===================================================================
> >>>--- bse/bsedatahandle-resample.cc	(revision 4068)
> >>>+++ bse/bsedatahandle-resample.cc	(working copy)
> >>>@@ -136,7 +136,7 @@ protected:
> >>> }
> >>>
> >>> /* implemented by upsampling and downsampling datahandle */
> >>>-  virtual BseResampler2Mode mode	() = 0;
> >>>+  virtual BseResampler2Mode mode	() const = 0;
> >>> virtual int64		    read_frame  (int64 frame) = 0;
> >>>
> >>>public:
> >>>@@ -222,18 +222,38 @@ public:
> >>>
> >>>   return n_values;
> >>> }
> >>>+  GslDataHandle*
> >>>+  get_source() const
> >>>+  {
> >>>+    return gsl_data_handle_get_source (m_src_handle);
> >>>+  }
> >>>+  int64
> >>>+  get_state_length() const
> >>>+  {
> >>>+    int64 source_state_length = gsl_data_handle_get_state_length
> >>>(m_src_handle);
> >>>+    if (source_state_length < 0)
> >>>+      return source_state_length;
> >>
> >>huh? why should a datahandle every return a negative state?
> >
> >Well, I thought of that line as a similar error propagation as I do in
> >read - that is, if the source handle does something strange, I pass it
> >on.
> >
> >What if the source handle had infinite state (like an IIR filter)?
> 
> then we return that, the best approximation would be G_MAXINT64.

When we introduce it, we will have to specialcase every computation with
states, as 2 * G_MAXINT64 and G_MAXINT64 + 31 is not G_MAXINT64. Such
computations can be found in the resampler already (and will probably
occur elsewhere).

So for now the code doesn't give G_MAXINT64 a special meaning.

> >Here is the new patch:
> 
> just pasting the changed portions would have been enough, it's not like the
> patch needed a major overhaul here. provided the above stuff is fixed it 
> should be ready to go in i think.

Committed.

   Cu... Stefan
-- 
Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan