[Kst] Getdata library

D. V. Wiebe dwiebe at physics.utoronto.ca
Wed Aug 22 21:42:19 CEST 2007

On Wed, Aug 22, 2007 at 11:39:25AM -0400, Adam D. Hincks wrote:
> 1.  Byte-swapping.  I have examined the source and it appears that there 
> are no provisions to do byte-swapping on differently-ended machines. 
> Right now we use all little-endian machines so this has not been an issue, 
> but we might do analysis in the future on architectures with different 
> byte orders.  (Our files will all be recorded little-endian.)  The 
> most convenient thing would be if getdata did byte-swapping somewhere in 
> the DoIfRaw() function.

I'm somewhat surprised it doesn't already do this.  AFAIK, kst is already
run on big endian systems.  Dirfiles are explicitly supposed to be stored
little endian.  How does kst currently deal with dirfiles in on big-endian

> 2.  A "truthful" version of GetNFrames().  GetNFrames() computes the 
> length of one of the files in the dirfile and uses that to compute the 
> number of frames.  Then it subtracts 2.  This is good when reading live 
> data as it avoids race conditions.  But with finished data sets we will 
> always be losing 2 seconds of data (our frames are ~1 second long).  We 
> would like a GetTrueNFrames().

This is a bug.  If applications using getdata (viz. kst) want to subtract
two from the number of available frames, they need to do that themselves.
It shouldn't happen in the library.

> 3.  "Ragged ends".  This is a bit more complicated to explain, but here 
> goes:
> Because of the nature of the ACT's data acquisition, we are unable to 
> guarantee that dirfiles will have a round number of frames.  On our 
> faster channels there will inevitably be a spill-over after the last frame 
> of a number of samples.  This number of samples will be the same for all 
> data at the same rate.  So, for example, if we have fields at 10 
> samples per frame (SPF), 5 SPF and 1 SPF, we could have after the last 
> frame:
>    10 SPF fields:  6 extra samples
>    5 SPF fields:   3 extra samples
>    1 SPF fields:   0 extra samples
> The following would also be possible:
>    10 SPF fields:  3 extra samples
>    5 SPF fields:   2 extra samples
>    1 SPF fields:   1 extra sample
> So we need a function to supplement GetNFrames().  This function would 
> return the number of extra samples after the last frame for a given field. 
> We can guarantee that data with the same SPF have the same number of extra 
> samples.

Are you asking for a GetNSamples, which would take a field name?

Don Wiebe                                       dwiebe at physics.utoronto.ca
Department of Physics
University of Toronto                           Office: ES4150
60 St. George St.                               Tele: +1-416-946-0946
Toronto ON  M5S 1A7                             Lab:  +1-416-946-0516
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