Michal Szpadzik wrote:
> I have some problems with bits data reading. I have binary data file where
> data is written as
> 12bits pack. I need to read it becouse there are saved values which have to
> processed later by my
> program. I was wandering about reading 3bytes=24bits and split it by bits
> moving. If anyone know
> how to do that please tell me or give me some code.
>
> My data example:
> 101001000101111010100101 etc
>
> i need to split it:
> x=101001000101 y=111010100101
assuming MSB first,
a = ord(fp.read(1))
b = ord(fp.read(1))
c = ord(fp.read(1))
x = (a << 4) + (b >> 4)
y = ((b & 15) << 8) + c
should do the trick
if you need to read lots of 12-bit values, you can create a simple bitstream
generator:
def bitstream(file, size=12):
bitbuffer = bits = 0
while 1:
char = file.read(1)
if not char:
raise StopIteration
bitbuffer = (bitbuffer << 8) | ord(char)
bits = bits + 8
while bits >= size:
yield (bitbuffer >> (bits - size)) & ((1 << size) - 1)
bits = bits - size
for example:
file = open("file.dat", "rb")
for word in bitstream(file):
print hex(word)
prints
0xa45
0xea5
</F>
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