/* Copyright (c) 2004 by R. A. Vowels.  Written August 2004.                                     */
 /* Permission is given to reproduce and to use these procedures                                  */
 /* as part of a program, and to include them as part of a larger work to be sold for profit.     */
 /* However, the user is not permitted to sell the procedures separately.  Provided always        */
 /* that these procedures and this copyright notice are reproduced in full.                       */

 /* This procedure converts a string of hexadecimal characters to characters.                     */
 /* Each pair of hexadecimal characters is translated to one character.                           */
 /* Invalid hexadecimal character pairs are translated to hex '00'.                               */

 unhex: procedure (hex) returns (char(16383) varying) options (reorder);
	dcl hex character (*);
	dcl 1 hs union,
		2 tr char (length(hex)),
		2 int(length(hex)) fixed binary(7);
	dcl 1 cs union,
		2 ci (0:length(hex)/2-1) fixed binary (7),
		2 s character (length(hex)/2);
	dcl i fixed binary (31);
	dcl (COLLATE, ISLL, ISRL, IAND, IOR, LENGTH, TRANSLATE) builtin;

	if iand(length(hex_string), 1) ^= 0 then
		do;
			put skip list ('The hexadecimal string does not have an even number of characters');
			signal error;
		end;

	tr = translate (hex, '0a0b0c0d0e0f0a0b0c0d0e0f00010203040506070809'x || (234)'00'x,
					'abcdefABCDEF0123456789' || COLLATE );

	do i = 1 to length(hex) by 2;
 (NOSIZE, NOFOFL):
		ci(isrl(i,1)) = ior(isll(int(i), 4), int(i+1));
	end;

	return (cs.s);

 end unhex;