[Python] In Matlab how to unpack a buffer of 12 bit values into an array of normalized float32

A measurement system (in our lab) produces data of 12 bits per sample in a packed format, i.e. 2 samples of 12 bits each are packed into 3 bytes:

buf[l + 2] | buf[l + 1] | buf[l + 0]
7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
-----------------------|-----------------------
B A 9 8 7 6 5 4 3 2 1 0|B A 9 8 7 6 5 4 3 2 1 0
sample[2*i + 1] | sample[2*i + 0]


For NumPy I created the following unpacking function that will take a Python byte buffer apply some stride tricks and bit manipulations to it, returning the desired float32 array:

def unpack_s12p_to_f32(buf):
import numpy
import numpy.lib.stride_tricks as npst
s12p = numpy.frombuffer(buf, dtype=numpy.int32)
s12p_sv = numpy.copy( numpy.transpose(
npst.as_strided(s12p,
shape=(2, int((s12p.size*4)/3)),
strides=(0,3), writeable=False) ))
m12b = (1<<12)-1
s12p_sv[:,0] &= m12b
s12p_sv[:,0] <<= 20
s12p_sv[:,1] >>= 12
s12p_sv[:,1] &= m12b
s12p_sv[:,1] <<= 20
return s12p_sv.reshape(-1).astype(numpy.float32) * (2.**-31)


We now seek a method to replicate this function within Matlab. However, I was unsuccessful finding/identifying equivalent functions that would allow me to manipulate Matlab array objects in the same way.

Example data and conversion result


From one of our datasets I extracted 200 samples. When written as Python buffer literal, passed through the above unpacking function and plotted using Matplotlib it looks like this

from matplotlib.pyplot import plot,show

data = \
b'\x19P\x05g\x90\x05I\x10\x01\xcf_\xfa\x87\x7f\xf5a\xbf\xf7\xb7\xff\xff9\xf0\x04]P' \
b'\x04)\x90\xfe\xad\xdf\xf6M\x1f\xf4s\x7f\xfb\xf5\x7f\x02=\xd0\x04W\xf0\x01\xfb\x7f' \
b'\xfb\x81\xff\xf6\x85\x7f\xf7\x8f\xbf\xfb\x05p\x03O\x90\x045\x90\x02\xf7\x7f\xfb' \
b'\x7f\xff\xf6q_\xf7\xb7\xff\xff!p\x03G\x90\x02\xdd\x7f\xfb\xc3\xdf\xf9s\xff\xf6' \
b'\x91?\xfb\xeb?\x011\xf0\x035\xb0\xff\xe1\xff\xfa\x81\xbf\xf6\x89\x9f\xf9\xc7\x9f' \
b'\xfe\r\x90\x02=\xf0\x02\x19\x90\xfe\xc3?\xf9\xa3\x1f\xfa\x8d\x7f\xf7\x99\xbf\xfc' \
b'\t\x10\x03=0\x02\x13\xb0\xfe\xb3?\xf8\x8b\xff\xf7\x83\xbf\xf9\xcd_\xfe\x050\x01' \
b'\x130\xff\xd3?\xfc\xb9\xbf\xfa\xa5\xdf\xf9\xa5_\xfc\xe9\xdf\xfe\xdb\xff\xfd\xf7' \
b'\x9f\xff\xe7\x9f\xfb\xcb?\xfc\xbd\xff\xf9\xab\xff\xfc\xfd\xdf\xff\xf2O\xfe\xe2\xcf' \
b'\xfc\xdc\xcf\xfc\xd4\xaf\xfd\xe8\xcf\xfd\xdc\xcf\xfd\xfc\x8f\x00\xfa\xaf\xfe\xec' \
b'\x0f\xfd\xc6/\xfc\xde\x0f\xff\xf2\xcf\xfd\xe2\x8f\xfe\xe8/\xff\xf4o\xfc\xce\xcf\xff' \
b'\x08@\xff\xf8\xef\xfd\xe8o\x00\x10`\xff\xe6/\xfd\xeco\xff\x06`\x00\xfe\x8f\xfe\xfa' \
b'\xef\xff\xe2\xaf\xfc\xdao\xfe\x00\x00\x00\xf8\x8f\xfd\xe0\xef\xfe\x00\xc0\xfe\xeao\xfe'

plot( unpack_s12p_to_f32(data) )
show()


producing the following output



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