%!
% From: roy@phri.UUCP (Roy Smith)
% Newsgroups: comp.lang.postscript
% Subject: Re: Building A PostScript Toolset
% Date: 30 Aug 89 17:20:01 GMT
% Organization: Public Health Research Inst. (NY, NY)
% 
% In <2251@optilink.UUCP> cramer@optilink.UUCP (Clayton Cramer) writes:
% > 3. To prevent creating write-only code, set variable names to stack
% > items at the start of the function [...] rather than using lots of dups,
% > exchs, and rolls
% 
% 	Well, here is a counter example.  I wrote this a while ago, and
% have used it several times.  It is a bunch of routines to let you work with
% vectors in 2-space (i.e. x,y coordinates).  It's all dups, exchs, and
% rolls.  Given the triviality of these, I think it's pretty easy to follow
% the thread of them, and it's all pretty well documented anyway.  But, yes,
% in general I agree -- code which does lots of fancy stack manipulation is
% hard to grok, even for somebody like me who grew up on HP (i.e. stack)
% machines.  I did a lot of up,up,rolldown,exchange stuff when I was hacking
% 9810's.  Obviously, the following can be extended, dot and cross products,
% and dimensions higher than 2, but that's all I needed so that's all I did.
% 
% -------------------
%
% vectorops.ps -- vector operators for PostScript.
%
% Copyright 1987 Roy Smith
% Permission is hereby granted for any use of this software other
% than selling it or including it in a commercial product.
%
% $Header: vectorops.ps,v 1.1 87/09/16 20:31:59 roy Exp $
%

% vadd -- add two vectors.
% x1 y1 x2 y2 vadd ==> x1+x2 y1+y2
/vadd
{
	3 -1 roll add		% ==> x1 x2 y2+y1
	3 1 roll add		% ==> y2+y1 x1+x2
	exch			% ==> x1+x2 y2+y1
} def

% vsub -- subtract two vectors.
% x1 y1 x2 y2 vsub ==> x1-x2 y1-y2
/vsub
{
	3 -1 roll sub neg	% ==> x1 x2 -(y2-y1)
	3 1 roll sub		% ==> -(y2-y1) x1-x2
	exch			% ==> x1-x2 -(y2-y1)
} def

% vneg -- take negative of vector (scalar multiply by -1).
% x y vneg ==> -x -y
/vneg
{
	exch neg		% ==> y -x
	exch neg		% ==> -x -y
} def

% vdiv -- divide vector by scalar.
% x y s vdiv ==> x/s y/s
/vdiv
{
	dup			% ==> x y s s
	3 1 roll div		% ==> x s y/s
	3 1 roll div		% ==> y/s x/s
	exch			% ==> x/s y/s
} def

% vmul -- multiply vector by scalar.
% x y s vmul ==> x*s y*s
/vmul
{
	dup			% ==> x y s s
	3 1 roll mul		% ==> x s y*s
	3 1 roll mul		% ==> y*s x*s
	exch			% ==> x*s y*s
} def

% vexch -- exchange two vectors on stack.
% x1 y1 x2 y2 vexch => x2 y2 x1 y1
/vexch
{
	4 2 roll		% ==> x2 y2 x1 y1
} def

% vpop -- pop a vector off the stack.
% x1 y1 vpop => ---
/vpop
{
	pop pop
} def

% vdup -- duplicate a vector on the stack.
% x1 y1 vdup => x1 y1 x1 y1
/vdup
{
	dup			% ==> x1 y1 y1
	3 -1 roll dup		% ==> y1 y1 x1 x1
	4 1 roll exch		% ==> x1 y1 x1 y1
} def
-- 
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu
"The connector is the network"