Implemented steps over a funge space field

2 files changed, 26 insertions, 0 deletions

diff --git a/src/field.nim b/src/field.nim
index e15d7b4..a9d706e 100644
--- a/src/field.nim
+++ b/src/field.nim
@@ -198,3 +198,18 @@ func Set*(f: var Field, x, y, v: int) =
       f.x = x
     if f.lx < x-f.x+1:
       f.lx = x-f.x+1
+
+func Step*(f: Field, v: tuple[x, y: int], d: tuple[x, y: int]): (int, int) =
+  var x = v.x + d.x
+  var y = v.y + d.y
+  if f.IsIn(x, y):
+    return (x, y)
+  # We are stepping outside, we need to wrap the Lahey-space
+  x = v.x
+  y = v.y
+  while true:
+    let x2 = x - d.x
+    let y2 = y - d.y
+    if not f.IsIn(x2, y2):
+      return (x, y)
+    x = x2; y = y2
diff --git a/tests/field.nim b/tests/field.nim
index dcb7530..e60887a 100644
--- a/tests/field.nim
+++ b/tests/field.nim
@@ -205,3 +205,14 @@ suite "Field":
     ])
     f.Set(-7, 4, int('y'))
     check f == xprependyappend
+  test "Step":
+    var minimal = Load("examples/minimal.b98")
+    var hello = Load("examples/hello.b98")
+    var dna = Load("examples/dna.b98")
+    check minimal[].Step((0, 0), (0, 0)) == (0, 0)
+    check minimal[].Step((0, 0), (1, 0)) == (0, 0)
+    check hello[].Step((3, 0), (0, 0)) == (3, 0)
+    check hello[].Step((3, 0), (1, 0)) == (4, 0)
+    check dna[].Step((1, 2), (3, 5)) == (4, 7)
+    check dna[].Step((6, 1), (1, 1)) == (5, 0)
+    check dna[].Step((1, 4), (-2, 2)) == (5, 0)