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Bitwise OR and Bitwise shift

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Das Siddharth
Das Siddharth 2021-4-26
评论： Walter Roberson 2021-4-26
I am trying to write a matlab code pretty much like the following C code :
uint8_t data[6];
uint32_t tdata = data[3] & 0x0F;
tdata <<= 8;
tdata |= data[4];
tdata <<= 8;
tdata |= data[5];
temperature = ((float)tdata * 200 / 0x100000) - 50;
I recently started using MATLAB and how I translated the above code is something like this :
uint32(tdata) = data(3) & 0x0F;
uint32(tdata) = bitshift(tdata,8);
uint32(tdata) = bitor(tdata,data(4));
uint32(tdata) = bitshift(tdata,8);
uint32(tdata) = bitor(tdata,data(5));
temperature = (tdata*200/1048576)-50;
It's throwing a lot of errors and I am quite stuck. Please help me out here. Thank you in advance.
  2 个评论
Matt J
Matt J 2021-4-26
编辑：Matt J 2021-4-26
We cannot run your code without being given "data" and "tdata".
Das Siddharth
Das Siddharth 2021-4-26
Actually, these are the datas I am getting from a sensor. It's in real-time. That's why I didn't post it here. I just wanted to know if we translate that code what's the correct way.

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回答（1 个）

Walter Roberson
Walter Roberson 2021-4-26
编辑：Walter Roberson 2021-4-26
temperature = double(bitand(data(4), 0x0f) * 65536 + data(5) * 256 + data(6)) * 200 / double(0x100000) - 50;
  2 个评论
Das Siddharth
Das Siddharth 2021-4-26
Wow ! Can we do this ? I mean without any bitshifts ? These are datas from an AHT20 temperature sensor btw.
Walter Roberson
Walter Roberson 2021-4-26
Use. You are using non-overlapping fields. Shift by multiplying, and add the components.
There are other ways of doing the calculation, but you run into hassles about the fact that MATLAB is little-endian on all current platforms, so doing bit operations is not the same as doing mathematical operations.
For example,
typecast( [data(6), data(5), bitand(data(4), 0x0f), uint8(0)], 'uint32') %slam together little-endian style

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