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Neo
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How to convert 24-bit signed hex from .csv file to an array of decimal data?

Asked by Neo
on 23 Jul 2019
Latest activity Commented on by Neo
on 23 Jul 2019
Accepted Answer by Jan
The csv file has content like below, the hexical data is signed 24-bit and has 0x prefix:
============
DATA
0xfd22cc
0xfe89d1
0xff8d8b
0x004b41
0x00d9d5
0x0125fa
==============
I have a few challenges, not quite good with coding with Matlab:
1) How to get rid of 0x prefix?
2) How to convert the signed 24-bit hex to decimal?
I came up with a really ugly code to do the work, but would love to learn a elegant way:
%% Read in data
dat = readtable('demo.csv');
dat1 = table2array(dat(:,1));
out = strip(dat1,'left','0');
out = strip(out,'left','x');
out_dec = typecast(uint32(base2dec(out, 16)), 'int32');
for i=1:length(out_dec)
if out_dec(i) < 2^23
out_signed(i) = out_dec(i);
else
out_signed(i) = out_dec(i) - 2^24;
end
end

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2 Answers

Answer by Jan
on 23 Jul 2019
 Accepted Answer

dataTable = readtable('demo.csv');
data = table2array(dataTable(:,1));
data = strrep(data, '0x', '');
dataDec = base2dec(data, 16);
index = dataDec >= 2^23;
dataDec(index) = dataDex(index) - 2^24;
I prefer the faster sscanf to convert hex strings to decimals.

  2 Comments

Note that:
data = table2array(dataTable(:,1));
is simply:
data = dataTable{:, 1};
%or
data = dataTable.(1);
%or
data = dataTable.Data;
very helpful, thanks.

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Answer by Guillaume
on 23 Jul 2019
Edited by Guillaume
on 23 Jul 2019

I agree with Jan that sscanf is nicer and for that reason:
dataTable = readtable('demo.csv');
dataDec = rowfun(@(s) sscanf(s, '%x'), dataTable, 'ExtractCellContents', true, 'OutputFormat', 'uniform')
dataDec(dataDec > 2^23) = dataDec(dataDec > 2^23) - 2^24;

  1 Comment

Very elegant as well, thanks.

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