def unpackints(data, dtype, itemsize, runlen=0):
"""Decompress byte string to array of integers of any bit size <= 32.
Parameters
----------
data : byte str
Data to decompress.
dtype : numpy.dtype or str
A numpy boolean or integer type.
itemsize : int
Number of bits per integer.
runlen : int
Number of consecutive integers, after which to start at next byte.
"""
if itemsize == 1: # bitarray
data = numpy.fromstring(data, '|B')
data = numpy.unpackbits(data)
if runlen % 8:
data = data.reshape(-1, runlen + (8 - runlen % 8))
data = data[:, :runlen].reshape(-1)
return data.astype(dtype)
dtype = numpy.dtype(dtype)
if itemsize in (8, 16, 32, 64):
return numpy.fromstring(data, dtype)
if itemsize < 1 or itemsize > 32:
raise ValueError("itemsize out of range: %i" % itemsize)
if dtype.kind not in "biu":
raise ValueError("invalid dtype")
itembytes = next(i for i in (1, 2, 4, 8) if 8 * i >= itemsize)
if itembytes != dtype.itemsize:
raise ValueError("dtype.itemsize too small")
if runlen == 0:
runlen = len(data) // itembytes
skipbits = runlen*itemsize % 8
if skipbits:
skipbits = 8 - skipbits
shrbits = itembytes*8 - itemsize
bitmask = int(itemsize*'1'+'0'*shrbits, 2)
dtypestr = '>' + dtype.char # dtype always big endian?
unpack = struct.unpack
l = runlen * (len(data)*8 // (runlen*itemsize + skipbits))
result = numpy.empty((l, ), dtype)
bitcount = 0
for i in range(len(result)):
start = bitcount // 8
s = data[start:start+itembytes]
try:
code = unpack(dtypestr, s)[0]
except Exception:
code = unpack(dtypestr, s + b'\x00'*(itembytes-len(s)))[0]
code <<= bitcount % 8
code &= bitmask
result[i] = code >> shrbits
bitcount += itemsize
if (i+1) % runlen == 0:
bitcount += skipbits
return result
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