Convert an array of type char to hex values

I have a character array read in from a csv

I want to convert the entire array to hex values before processing the data

This saves me computation time by not having to call hex2dec or hex2binaryvector 50000 times

Anyone have any ideas?

Answer 1

[Walter Roberson]

I showed you a number of different methods in https://www.mathworks.com/matlabcentral/answers/888752-quickest-way-to-convert-hex-to-a-16-bit-signed-integer#answer_756857 and showed timings of each.

The edit I just made, to use a lookup table, is the fastest method yet, more than 50 times faster than dec2hex()

Answer 2

[dpb]

I went back and found your first posing of roughly a week ago -- and made a comment there.

In short, take Walter's advice from back then and use either textscan for fscanf or readmatrix and do the conversion on input inside the C i/o library instead.

Not being willing to share anything; even a dummy-data file of typical structure pretty-much limits how much more specific can get.

[Robert Scott]

I have been trying to do that

I have gotten away from tables and moved to readmatrix

What i need to do is readmatrix using the number system hex

But i have been unable to figure out how to do that. I have posted in the thread about it but i guess no one has seen it yet

Can you tell me how to readmatrix() a csv file with a number system of hex?

I have not found any property in any of the help files called "number system"

[dpb]

Is the full array hex? And how encoded in the file?

[Robert Scott]

its a .csv file

It is hex with the exception of the first and last col

Not sure what you mean by encoded

[dpb]

"It is hex with the exception of the first and last col"

So what are they? Format has to match column by column to read proper types; otherwise one gets what MATLAB thinks should be -- and default as you've discovered is that hex comes in as char()

"what you mean by encoded"

Is there any leading 0X prefix or the like in the file or just string of hex digits.

The format string encoding textscan uses for hex inputs is as follows: <textscan formatSpec>

                                     Conversion        Output
                                      Specifier         Class
Hexadecimal number, unsigned integer    %xu             int64
                                        %xu8u           int8
                                        %xu16u          int16
                                        %xu32u          int32
                                        %xu64u          int64
Hexadecimal number, signed integer      %xs8            int8
                                        %xs16           int16
                                        %xs32           int32
                                        %xs64           int64

So, which of the above are your values?

Again, it would be SO much easier if you would just attach a small sample file, even if the data are random -- and there's absolutely nothing anybody could do with a set of hex numbers in isolation, even if they were the real thing.

If there's something proprietary in the first/last column, that could be obfuscated as long as it was same data type.

But, I did discover one thing I was not aware of that had presumed was so since was in Walter's earlier response -- readtable and friends have not yet been extended to accept the hex type as input -- why, I've no idea; seems a glaring oversight.

So, we are down to lower-level routines, but if speed is the intent, they're better, anyways, just a little more up front work--although Walter also showed that by lookup table the conversion from hex can be pretty quick.

One last Q? on the file structure -- is the size known a priori or can it be inferred from some other piece of information or is it unknown in length but fixed number of columns or both? It's most important to know how many columns although that can be found out by reading the first record and counting delimiters, if is known a priori can save the step as well as dynamic building of a format string to match in favor of fixed one.