bitstreams

[Michael Hudson]

Andreas Lobinger <andreas.lobinger at netsurf.de> writes:

> Aloha,
> can anyone here recommend a implementation for bitstreams?
> 
> For a project i need to extract bitfields from a file containing
> one large bitstream (lenght >> 1000bit). The bitfields (1bit-24bit)
> are not aligned to char boundaries (8bit).
> 
> Something like
> b1 = bitstream.fromfile('m1.bin')
> v1 = b1.getbits(startpos=3,length=10) # v ist a reg. int
> v2 = b1.getnext(8) # bits 0-7
> v3 = b1.getnext(10) # bits 8-17

Well, a thousand bits really isn't very many.  Read the lot and slurp
it into a long?  Hmm, not sure of an easy way to do that... something
like 

a = array.array('B')
a.fromstring(open('m1.bin').read())
v = 0L
m = 1L
for b in a:
    v += m*b
    m *= 256

then use shifts & masks as desired on v.

There ought to be a cuter way to go from m1.bin to v, though...

Cheers,
mwh

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