[Scilab-Dev] save(..) with internal timestamp? MD5 varying with unchanged content to be saved.

[Samuel Gougeon]

Hi,

I have N figures. I would like to re-export only those that were 
modified in the meanwhile.
Indeed, exporting with xs2### is rather time-consuming, in such a way 
that i am looking for a short-circuit.

The way that i imagined is the following, for a figure of handle f :
1) f is saved in file1.sod. This is quite faster than exporting.
2) later, f is re-saved in file2.sod
3) we compute the MD5 checksums of the contents of file1.sod and file2.sod
4) we compare both checksums. If they are different, we re-export f.

Unfortunately, it looks that save(..) likely saves also an internal 
timestamp, or something varying external to the main saved content.
This ruins the idea, and i do not see any reflief plan. Here is a proof:

clf
plot2d()
f  =  gcf();
save  test.sod  f
getmd5  test.sod
sleep(5000)
save  test.sod  f
getmd5  test.sod   

Yielding:

-->clf
-->plot2d()
-->f = gcf();
-->save test.sod f
-->getmd5 test.sod
  ans  =
  e015481486eb9708a4fe1d3df1cbbbb9
-->sleep(5000)
-->save test.sod f
-->getmd5 test.sod
  ans  =
  3c6319b5d3a2299caaacc2f95c3efb32

Other tests show that
1) renaming the file does not change its checksum returned by getmd5()
2) modifying the OS timestamp of the file (any of creation, last access, 
last write) does not change its checksum.

Hence, it really looks that an internal timestamp is recorded with the 
proper data.
So, my questions are :
1) do -- you developers -- confirm this save()'s behavior? I did you go 
the the source code.
2) Why doing that? Is is on purpose, or is it a bug?
3) Is there a way to avoid it?
     a) There is presently no usage option to avoid it
     b) On option, recording only the date with a fixed conventionnal 
hour such that 00:00:00.000 would be ok for me.
         10s of export is <<< 24h ;)
4) Would you have any idea to do what i expect with figures, without 
using their saved handles?
     I posted a wish and proposal 
http://bugzilla.scilab.org/show_bug.cgi?id=11658  3 years ago, in order to
     open the possibillity to save copies of handles (in structures) and 
then becomes able to compare them.
     But the thread does not breathe...

Reading you soon

Samuel

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