harvey/sys/src/cmd/gs/lib/type1enc.ps

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% $Id: type1enc.ps,v 1.2 2000/09/19 18:29:11 lpd Exp $
% type1enc.ps
% PostScript language versions of the Type 1 encryption/decryption algorithms.

% This file is normally not needed with Ghostscript, since Ghostscript
% implements these algorithms in C.  For the specifications, see Chapter 7 of
% "Adobe Type 1 Font Format," ISBN 0-201-57044-0, published by Addison-Wesley.

/.type1crypt	% <R> <from> <to> <proc> .type1crypt <R'> <to>
		% (auxiliary procedure)
 { 4 1 roll
   0 2 index length getinterval
   0 1 2 index length 1 sub
    {		% Stack: proc R from to index
      2 index 1 index get			% proc R from to index C/P
      4 index -8 bitshift xor 3 copy put	% proc R from to index P/C
      5 index exec				% proc R from to C

%		Compute R' = ((R + C) * 52845 + 22719) mod 65536
%		without exceeding a 31-bit integer magnitude, given that
%		0 <= R <= 65535 and 0 <= C <= 255.

      4 -1 roll add
      dup 20077 mul	% 52845 - 32768
      exch 1 and 15 bitshift add	% only care about 16 low-order bits
      22719 add 65535 and 3 1 roll
    }
   for exch pop 3 -1 roll pop
 } bind def

% <state> <fromString> <toString> .type1encrypt <newState> <toSubstring>
%	Encrypts fromString according to the algorithm for Adobe
%	  Type 1 fonts, writing the result into toString.
%	  toString must be at least as long as fromString or a
%	  rangecheck error occurs.  state is the initial state of
%	  the encryption algorithm (a 16-bit non-negative
%	  integer); newState is the new state of the algorithm.

/.type1encrypt
 { { exch pop } .type1crypt
 } bind def

% <state> <fromString> <toString> .type1decrypt <newState> <toSubstring>
%	Decrypts fromString according to the algorithm for Adobe
%	  Type 1 fonts, writing the result into toString.  Other
%	  specifications are as for type1encrypt.

/.type1decrypt
 { { pop 2 index exch get } .type1crypt
 } bind def