[Octave-bug-tracker] [bug #31942] Save/load single precision variables with MATLAB data format fails

[David Bateman]

Follow-up Comment #9, bug #31942 (project octave):

I'm starting to remember why I hate the matlab file format.... 

The new issue has to do with the way matlab treats small (tag,value) pairs.
That is a matlab data element is made up of a number of pairs (tag,value)
where the tag contains the type of the value and its size in bytes. Typically
the tag is 8 bytes with 4 bytes of the type followed by 4 bytes for the length
of value.. and here's the catch. If the size saved in the tag is 4bytes of
less, then the type is coded in 2 bytes, the length in two bytes and the data
in four bytes!

As the length of a single element in the double type is 8 bytes they were
never saved with short tags.. Single elements of the single type however are.
So when calculating the length of the data to be saved we now need to take
into account short tags for the single precision type.. My copy-paste to
create the single-precision load/save code didn't take this into account.

I've attached a new changeset and hopefully this time there are no further
issues. The new patch also avoids some copying when calculating the element
length by casting the arrays as const.

Given the past history of this bug I won't commit this and close this bug
till I have a report that there aren't any other issues.

D.

(file #22365)
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Additional Item Attachment:

File name: changeset2.single              Size:3 KB


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