gEDA-dev: gerbv mis-parses aperture macro definitions

[Bernd Jendrissek]

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Below is a reduced gerber from a board we produce that I tried to view
with gerbv.  It looked good where it was right but unfortunately it had
some ghastly diagonal lines across several layers.

The problem seems to be that gerbv cannot parse the following two lines
in the aperture macro MTHOLE definition:

$1=$1-$2*
$1=$1/2*

I had a look through src/amacro.c and unfortunately fixing this would
exceed the trivial-change copyrightability threshold.  It would need
either a proper precedence-aware parse, or a simple right-to-left rule.

There's an implementation of infix to postfix conversion at
http://andrewd.ces.clemson.edu/courses/cpsc215/spring01/hw/asg2/cal.c
The comment right above in2post() outlines the algorithm.

%IN114-35D.IN2*%
%ICAS*%
%MOMM*%
G04*
G04  Aperture MACROs for general use --- invoked via D-code assignment *
G04*
G04  General MACRO for mounting hole *
%AMMTHOLE*
1,1,$1,0,0*
1,0,$2,0,0*
$1=$1-$2*
$1=$1/2*
21,1,$2+$1,$3,0,0,$4*
21,1,$3,$2+$1,0,0,$4*%
G04*
G04  D59 : "Ellipse X1.700mm Y1.700mm H0.000mm 0.0deg (0.000mm,0.000mm) Flash"*
G04  Disc: OuterDia=1.7000*
%ADD59C, 1.7000*%
G04  D74 : "Mounting Hole X7.000mm Y7.000mm H0.000mm 0.0deg (0.000mm,0.000mm) Flash"*
G04  Mounting Hole: Diameter=7.0000, Rotation=0.0, LineWidth=0.1270 *
%ADD74MTHOLE, 7.0000 X6.4920 X0.1270 X0.0*%
G04*
%FSLAX44Y44*%
%SFA1B1*%
%OFA0.000B0.000*%
G04*
G71*
G90*
G01*
D59*
X4000050D3*
D74*
Y1068200D3*
D02M02*

- -- 
Q: Why does this scheme have so many keys?
A: We added them as the need arose.
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