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Why3
why3
Commits
1f34a803
Commit
1f34a803
authored
Mar 25, 2010
by
Jean-Christophe Filliâtre
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nettoyage
parent
a4ddea0c
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examples/programs/bresenham.mlw
examples/programs/bresenham.mlw
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examples/programs/bresenham.mlw
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1f34a803
(* Bresenham line drawing algorithm. *)
(* Parameters.
Without loss of generality, we can take [x1=0] and [y1=0].
Thus the line to draw joins [(0,0)] to [(x2,y2)]
and we have [deltax = x2] and [deltay = y2].
Moreover we assume being in the first octant, i.e.
[0 <= y2 <= x2]
(see the Coq file)
. The seven other cases can be easily
[0 <= y2 <= x2]. The seven other cases can be easily
deduced by symmetry. *)
{
logic x2 : int
logic y2 : int
axiom First_octant : 0 <= y2 and y2 <= x2
}
(* Global variables of the program. *)
(* The code.
[(best x y)] expresses that the point [(x,y)] is the best
possible point i.e. the closest to the real line (see the Coq file).
...
...
@@ -40,7 +41,7 @@ let bresenham =
while !x <= x2 do
invariant {0 <= !x and !x <= x2 + 1 and invariant(!x, !y, !e) }
variant { x2 + 1 - !x }
(* here we would
do (
plot
x
y) *)
(* here we would plot
(x,
y) *)
assert { best(!x, !y) };
if !e < 0 then
e := !e + 2 * y2
...
...
@@ -52,9 +53,8 @@ let bresenham =
done
(*
Local Variables:
compile-command: "unset LANG; make -C ../..
testl
"
compile-command: "unset LANG; make -C ../..
examples/programs/bresenham
"
End:
*)
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