quickest way to convert hex to a 16 bit signed integer

Question

Robert Scott 2021-7-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/888752-quickest-way-to-convert-hex-to-a-16-bit-signed-integer

评论： Walter Roberson 2021-8-6

采纳的回答： Walter Roberson

looking for the quickest way to convert 16 bit hex into a singed 16 bit int

performance is key here.

I was doing it with a type cast before but appears very slow

Anyone have any ideas?

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James Tursa 2021-7-29

Please provide details of exact input and desired output. Is the hex in a char array? What size? What is the exact code you have tried so far?

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Answer 1

Walter Roberson 2021-7-29

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/888752-quickest-way-to-convert-hex-to-a-16-bit-signed-integer#answer_756857

编辑：Walter Roberson 2021-7-31

format long g
N = 100000;
HC = ['0':'9', 'A':'F'];
data = HC(randi(16, N, 4));
timeit(@() typecast(uint16(hex2dec(data)),'int16'), 0)
ans = 
               0.078666781
timeit(@() typecast(uint16(sscanf(data.', '%4x')),'int16'), 0)
ans = 
               0.010088781
timeit(@() typecast(cell2mat(textscan(strjoin(cellstr(data),'\n'),'%xu16')),'int16'), 0)
ans = 
               0.114500781
timeit(@() cell2mat(textscan(strjoin(cellstr(data),'\n'),'%xs16')), 0)
ans = 
               0.114293781
timeit(@() via_ismember_typecast(data, HC), 0)
ans = 
               0.003229781
timeit(@() via_ismember_no_typecast(data, HC), 0)
ans = 
               0.004451781
timeit(@() via_math_typecast(data, HC), 0)
ans = 
               0.005474781
timeit(@() via_discretize_typecast(data, HC), 0)
ans = 
               0.005370781
timeit(@() via_lookup_typecast(data,HC), 0)
ans = 
               0.001278781
function num = via_ismember_no_typecast(data, HC)
   [~, dec] = ismember(data, HC);
   num = dec(:,1)*4096 + dec(:,2)*256 + dec(:,3) * 16 + dec(:,4);
   mask = num > 32767;
   num(mask) = num(mask) - 65536;
   num = int16(num);
end
function num = via_ismember_typecast(data, HC)
   [~, dec] = ismember(data, HC);
   dec = dec-1;   %bin numbers start with 1
   num = typecast(uint16(dec(:,1)*4096 + dec(:,2)*256 + dec(:,3) * 16 + dec(:,4)),'int16');
end
function num = via_math_typecast(data, HC)
   dec = data - '0';
   mask = dec>9;
   dec(mask) = dec(mask) - 7;
   num = typecast(uint16(dec(:,1)*4096 + dec(:,2)*256 + dec(:,3) * 16 + dec(:,4)),'int16');
end
function num = via_discretize_typecast(data, HC)
  dec = discretize(double(data), double(HC)) - 1;  %bin numbers start with 1
  num = typecast(uint16(dec(:,1)*4096 + dec(:,2)*256 + dec(:,3) * 16 + dec(:,4)),'int16');
end
function num = via_lookup_typecast(data, HC)
   lookup(HC) = 0:15;
   dec = lookup(data);
   num = typecast(uint16(dec(:,1)*4096 + dec(:,2)*256 + dec(:,3) * 16 + dec(:,4)),'int16');
end

So via_lookup_typecast is the fastest of these, and via_ismember_typecast is second fastest out of all of these possibilities.

If you are doing a lot of these conversions, then the lookup table can be precomputed -- and it is easy to extend the lookup table to handle lowercase as well as upper case.