From 778d04ce21172bb1ed068176c4c38bb0a39767b4 Mon Sep 17 00:00:00 2001
From: Karol Stasiak <karol.m.stasiak@gmail.com>
Date: Sat, 3 Aug 2019 20:33:49 +0200
Subject: [PATCH] 6502: Fix sign extension when type casting

---
 .../compiler/mos/MosExpressionCompiler.scala  |  4 ++-
 .../millfork/test/SignExtensionSuite.scala    | 30 ++++++++++++++++++-
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
index 4b27c17d..d20d1e9a 100644
--- a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
+++ b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
@@ -1635,7 +1635,9 @@ object MosExpressionCompiler extends AbstractExpressionCompiler[AssemblyLine] {
             env.maybeGet[Type](f.functionName) match {
               case Some(typ) =>
                 val sourceType = validateTypeCastAndGetSourceExpressionType(ctx, typ, params)
-                val newExprTypeAndVariable = exprTypeAndVariable.map(i => sourceType -> i._2)
+                val newExprTypeAndVariable = exprTypeAndVariable.map { i =>
+                  (if (i._1.size == sourceType.size) i._1 else sourceType) -> i._2
+                }
                 return compile(ctx, params.head, newExprTypeAndVariable, branches)
               case None =>
                 // fallthrough to the lookup below
diff --git a/src/test/scala/millfork/test/SignExtensionSuite.scala b/src/test/scala/millfork/test/SignExtensionSuite.scala
index 35ef261f..545790da 100644
--- a/src/test/scala/millfork/test/SignExtensionSuite.scala
+++ b/src/test/scala/millfork/test/SignExtensionSuite.scala
@@ -1,7 +1,7 @@
 package millfork.test
 
 import millfork.Cpu
-import millfork.test.emu.EmuCrossPlatformBenchmarkRun
+import millfork.test.emu.{EmuCrossPlatformBenchmarkRun, EmuUnoptimizedCrossPlatformRun}
 import org.scalatest.{FunSuite, Matchers}
 
 /**
@@ -69,4 +69,32 @@ class SignExtensionSuite extends FunSuite with Matchers {
       m.readWord(0xc000) should equal(440)
     }
   }
+
+  test("Byte to Word") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80)("""
+        | word output @$c000
+        | void main () {
+        |   sbyte b
+        |   b = -1
+        |   memory_barrier()
+        |   output = byte(b)
+        | }
+      """.stripMargin){m =>
+      m.readWord(0xc000) should equal(0x00ff)
+    }
+  }
+
+  test("Byte to Word 2") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80)("""
+        | word output @$c000
+        | void main () {
+        |   sbyte b
+        |   b = -1
+        |   memory_barrier()
+        |   output = word(byte(b))
+        | }
+      """.stripMargin){m =>
+      m.readWord(0xc000) should equal(0x00ff)
+    }
+  }
 }