base64 encoder in postscript

base64.ps

/base64EncodingTable [
	(A) (B) (C) (D) (E) (F) (G) (H) (I) (J)
	(K) (L) (M) (N) (O) (P) (Q) (R) (S) (T)
	(U) (V) (W) (X) (Y) (Z) (a) (b) (c) (d)
	(e) (f) (g) (h) (i) (j) (k) (l) (m) (n)
	(o) (p) (q) (r) (s) (t) (u) (v) (w) (x)
	(y) (z) (0) (1) (2) (3) (4) (5) (6) (7)
	(8) (9) (+) (/)
] def

% takes 3 bytes and returns their 4 base64 encoded values
/threeBytesToFourChars {
	/b3 exch def
	/b2 exch def
	/b1 exch def

	% first 6 of b1
	/c1 b1 2#11111100 and -2 bitshift def

	% last 2 of b1, first 4 of b2
	/c2
		b1 2#00000011 and 4 bitshift  % last 2 of b1
		b2 2#11110000 and -4 bitshift % first 4 of b2
		xor
	def

	% last 4 of b2, first 2 of b3
	/c3
		b2 2#00001111 and 2 bitshift  % last 4 of b2
		b3 2#11000000 and -6 bitshift % first 2 of b3
		xor
	def

	% last 6 of b3
	/c4 b3 2#00111111 and def
	c4 c3 c2 c1
} def

% (a) (b) -> (ab)
% https://stackoverflow.com/questions/12378904/postscript-concatenate-two-strings
/concat { exch dup length    
	2 index length add string    
	dup dup 4 2 roll copy length
	4 -1 roll putinterval
} bind def 

% TODO: Fix for non mod 3 strings
/base64Encode {
	/inputString exch def
	/outputString () def
	0 3 inputString length 1 sub {
		/i exch def
		/curChars [
			inputString i 3 getinterval
			{} forall
			threeBytesToFourChars 
		] def
		/curOut () def
		curChars {
			/curChar exch def
			/curOut base64EncodingTable curChar get curOut concat def
		} forall
		/outputString outputString curOut concat def
	} for
	outputString
} def