Fix for i,const,downto,0 loops

src/main/scala/millfork/compiler/StatementCompiler.scala

@@ -419,8 +419,8 @@ object StatementCompiler {
             Nil
           case (ForDirection.DownTo, Some(NumericConstant(s, ssize)), Some(NumericConstant(0, esize))) if s > 0 =>
             compile(ctx, List(
-              Assignment(vex, f.start),
-              DoWhileStatement(f.body, List(decrement), FunctionCallExpression("!=", List(vex, f.end)), names)
+              Assignment(vex, SumExpression(List(false -> f.start, false -> LiteralExpression(1, 1)), decimal = false)),
+              DoWhileStatement(decrement :: f.body, Nil, FunctionCallExpression("!=", List(vex, f.end)), names)
             ))
 
 

src/test/scala/millfork/test/ForLoopSuite.scala

@@ -54,6 +54,27 @@ class ForLoopSuite extends FunSuite with Matchers {
         | }
       """.stripMargin)(_.readByte(0xc000) should equal(15))
   }
+
+  test("For-downto 2") {
+    EmuBenchmarkRun(
+      """
+        | array output [55] @$c000
+        | void main () {
+        |   byte i
+        |   output[0] = 0
+        |   output[5] = 0
+        |   output[6] = 0
+        |   for i,5,downto,0 {
+        |     output[i] += 1
+        |   }
+        | }
+      """.stripMargin){m =>
+      m.readByte(0xc000) should equal(1)
+      m.readByte(0xc005) should equal(1)
+      m.readByte(0xc006) should equal(0)
+    }
+  }
+
   test("For-until") {
     EmuBenchmarkRun(
       """