12.10.09

asc-gzip/.xfd decompression

Posted in General at 11:30 am by Steven

Scott Stafford was nice enough to post code for asc-gzip/.xfd decompression to go with my asc-gzip/.xfd compression code. See this comment. I’m also reposting it here because the comment formatting is a little more bad than the main-post formatting.

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Thanks for your post. Of course, I needed the opposite, I had one I needed to decompress. So I backwarded your algorithm and here is the result:

def decompress(fc):
    fc2 = fc.splitlines(True)
    fc3 = "".join(fc2[1:]) # could verify that it's asc-gzip here if we wanted to...
    unb64 = base64.standard_b64decode(fc3)

    ctr = 0
    ret = []
    while 1:
        if ctr == len(unb64): break

        ccltop = ord(unb64[ctr])
        ctr += 1
        cclbottom = ord(unb64[ctr])
        ctr += 1
        compressedchunklen = ccltop * 256 + cclbottom

        cltop = ord(unb64[ctr])
        ctr += 1
        clbottom = ord(unb64[ctr])
        ctr += 1
        chunklen = cltop * 256 + clbottom
        #~ print compressedchunklen, chunklen

        compressedchunk = unb64[ctr:ctr+compressedchunklen]
        ctr += compressedchunklen

        chunk = zlib.decompress(compressedchunk)
        assert(len(chunk) ==  chunklen)
        ret.append(chunk)

    return "".join(ret)

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