Here, for comparison, is a RiscLua version of Base64 encoding/decoding.

#! lua
local char in string
local concat in table
local pairs = pairs
module "base64" -- exports encode,decode
 local f = \ (self, z) self[1 + #self] = z end
 local stk = \ ( ) => { push = f } end
 local C = { } -- encryption table
 for i = 0, 25 do
 C[i], C[26+i] = char (65+i), char (97+i) -- upper/lower case letters
 end
 for i = 52, 61 do C[i] = char (i-4) end -- digits
 C[62], C[63] = '-','_' -- 2 extra +,/ for standard
 encode = \ (data)
 local bb, x, r = { }, stk ( ), nil
 for s = 0, #data - 1, 3 do
 for b = 1, 3 do bb[b] = (data:sub (s + b)):byte ( ) or 0 end
 r = #data - s
 x:push (C[bb[1] >> 2])
 x:push (C[((bb[1] % 4) << 4) | (bb[2] >> 4)] or "=")
 x:push (r>1 and C[((bb[2] % 16) << 2) | (bb[3] >> 6)] or "=")
 x:push (r>2 and C[bb[3] % 64] or "=")
 end -- for
 => concat (x) end -- function
 local B = { } -- decryption table
 for key, value in pairs (C) do B[value] = key end -- invert C
 decode = \ (data)
 local cc, y, n, j = { }, stk ( ), 256, nil
 for d = 0, #data - 1, 4 do
 for c = 1, 4 do j = d + c; cc[c] = B[data:sub (j,j) or "="] end
 y:push (char (((cc[1] << 2) % n) | (cc[2] >> 4)))
 y:push (cc[3] and char (((cc[2] << 4) % n) | (cc[3] >> 2)) or "")
 y:push (cc[4] and char ((((cc[3] << 6) % n) % 192) | cc[4]) or "")
 end -- for
 => concat (y) end -- function
-- end module

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Last edited March 30, 2014 7:26 am GMT (diff)