[gnuastro-devel] [task #14154] Avoid reading a single file and header more than once

[Mohammad Akhlaghi]

URL:
  <http://savannah.gnu.org/task/?14154>

                 Summary: Avoid reading a single file and header more than
once
                 Project: GNU Astronomy Utilities
            Submitted by: makhlaghi
            Submitted on: Fri 09 Sep 2016 11:51:47 PM JST
         Should Start On: Fri 09 Sep 2016 12:00:00 AM JST
   Should be Finished on: Fri 09 Sep 2016 12:00:00 AM JST
                Category: Arithmetic
                Priority: 5 - Normal
              Item Group: Enhancement
                  Status: Postponed
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                  Effort: 0.00

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Details:

In Arithmetic, it is sometimes necessary to use the pixels of a sepecial HDU
(one extension of a FITS file) more than once in one run. Especially now that
conditional operators and the where operator are also included.

The way Arithmetic currently works is that it will read each HDU every time it
confronts one on the command-line, it will then free it and the next time the
same HDU comes up, it is read in again from the FITS file. For small files the
CPU cache might be useful, but for common FITS images, it will fill up soon.

It is not hard to add a step which will check all the input HDUs (FITS files
and extensions) and if there is more than one occurance of a specific HDU, it
will read it and keep it in a special place in memory. This way, any time we
need it we can just copy and use it. Also, since we know the total number of
times it is being used, for the last time, we can just pass its pointer so it
is free automatically by the operator. This process will avoid reading it a
second, third, or any more number of times and thus greatly speed up its
processing. 

I currently don't have the time to implement this, but if you are up to it,
state your interest here and take up this task ;-).




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