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QR Decoder

Details

Decode a Version-1 QR code given in this ASCII-art format, where all the v and ^ are filled with "#" and spaces, encoding a message.

    #######  vv^^ #######
    #     #  vv^^ #     #
    # ### # #vv^^ # ### #
    # ### #  vv^^ # ### #
    # ### #  vv^^ # ### #
    #     #  vv^^ #     #
    ####### # # # #######
            #vv^^
    ### #####vv^^##   #
    vv^^vv ^^vv^^vv^^vv^^
    vv^^vv#^^vv^^vv^^vv^^
    vv^^vv ^^vv^^vv^^vv^^
    vv^^vv#^^vv^^vv^^vv^^
            #vv^^vv^^vv^^
    ####### #vv^^vv^^vv^^
    #     # #vv^^vv^^vv^^
    # ### # #vv^^vv^^vv^^
    # ### #  vv^^vv^^vv^^
    # ### # #vv^^vv^^vv^^
    #     # #vv^^vv^^vv^^
    ####### #vv^^vv^^vv^^

The 10 vertical "strips" of ^^ or vv must be read from right to left. The bits in a strip are stored in a zig-zag order: ^^ zig-zags upwards, and vv zig-zags downwards. The bit on the right always precedes the one on its left.

      ^^ ..       vv 10
      ^^ 98       vv 32
      ^^ 76       vv 54
      ^^ 54       vv 76
      ^^ 32       vv 98
      ^^ 10       vv ..

To decode a bit off of a strip, read the value from the QR code bitmap ("#" = 1, space = 0) and invert it if (x+y)%2 = 0, where (x, y) are the coordinates of the bit in the bitmap with the origin (0, 0) at the top-left corner.

This will yield a bitstream like:

    0100  00010001  01001000  01100101  01101100 ...
    Enc   Length    'H'       'e'       'l'
    (4)   (17)      (17-byte ASCII message)

Print the 17 bytes of ASCII stored in the QR code.

0 bytes, 0 chars
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Compiled from AT&T syntax to x86-64 Linux. Use syscalls to write output.
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