[lifthrasiir]

It would have been better to have an algorithm description somewhere, but it is not hard to follow. So crzy64 is essentially base64 plus two optimizations:

- Output bytes [A-Za-z0-9./] are shuffled so that it can be efficiently translated from and to the 0..63 range. The exact remapping is as follows:

    cDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz./0123456789AaBbC

- Bits are reordered and XORed with each other to make the unpacking from three 8-bit bytes to four 6-bit units extremely simple: specifically, `x ^ (x >> 6)`. The input bits `qrstuvwx ijklmnop abcdefgh` thus should be converted to the following four 6-bit units, XORed together (here represented with two-bit padding as in the actual implementation):

    00abcdef 00ijklgh 00qrmnop 00stuvwx
    0000ijkl 00000000 0000gh00 00mnop00
    000000qr 00000000 00000000 00gh0000

Since both optimizations can equally work well for SIMD and for SWAR (SIMD within a register), I guess they may even be useful for small inputs.

[jpegqs]

Great description, but there is a typo in the second row:

    00000000 abcdefgh ijklmnop qrstuvwx
    -------- -------- -------- --------
    00abcdef 00ijklgh 00qrmnop 00stuvwx
    0000ijkl 0000qr00 0000gh00 00mnop00 <-- missing "qr"
    000000qr 00000000 00000000 00gh0000

[jpegqs]

Still can't improve this stage of encoding, it requires a lot of operations. Maybe there is something trivial, but I don't see it.