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memmapfile and importing big-endian data

Asked by D. Plotnick on 11 Apr 2017
Latest activity Commented on by D. Plotnick on 12 Apr 2017
I need to import a large mixed-format binary file. This is best done using memmapfile. However, the data has also been written in big-endian.
Short of a time consuming loop through the 50,000 lines of the structure, and all of the associated structure fields, is there any way to reverse the endian-ness of everything that comes out of the Data field from memmapfile?
Alternatively, I could do some gruesome struct2cell juggling.Yuck.
Bottom line: is there a way to reverse the endian-ness of memmapfile? If not, that should be added.

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1 Answer

Answer by Steven Lord
on 12 Apr 2017
 Accepted Answer

I don't believe you can control whether memmapfile treats the file as little-endian or big-endian. You can use the swapbytes function on the data to flip it between the two endian-nesses.

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That is what I am currently doing, but it is a very slow operation on the order of 20x+ the time required to do the initial import. There are over 600,000 entries in this file alone, each with multiple entries of mixed format that need to be swapped, and the loop through (or as I have written it, cellfun) is a real drag on the code performance.
Since the importation itself using memmapfile is so fast, there must be a better way of doing this.

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