Generate checksums for Game Boy

docs/api/custom-platform.md

@@ -162,3 +162,5 @@ Default: `after_code`.
 * `extension` – target file extension, with or without the dot
 
 * `bbc_inf` – should the `.inf` file with file metadata for BBC Micro be created
+
+* `gb_checksum` – should the main output file be patched with Game Boy-compatible checksums

src/main/scala/millfork/Main.scala

@@ -106,6 +106,12 @@ object Main {
     result.code.foreach{
       case (bankName, code) =>
         val prgOutput = if (bankName == "default") {
+          if (platform.generateGameBoyChecksums) {
+            code(0x14d) = (0x0134 to 0x14c).map(code).map(_^0xff).sum.toByte
+            val globalChecksum = code.map(_&0xff).sum
+            code(0x14f) = globalChecksum.toByte
+            code(0x14e) = globalChecksum.>>(8).toByte
+          }
           defaultPrgOutput
         } else {
           s"${output.stripSuffix(platform.fileExtension)}.$bankName${platform.fileExtension}"

src/main/scala/millfork/Platform.scala

@@ -31,6 +31,7 @@ class Platform(
                 val freeZpPointers: List[Int],
                 val fileExtension: String,
                 val generateBbcMicroInfFile: Boolean,
+                val generateGameBoyChecksums: Boolean,
                 val bankNumbers: Map[String, Int],
                 val defaultCodeBank: String,
                 val outputStyle: OutputStyle.Value
@@ -193,6 +194,7 @@ object Platform {
     }.toList)
     val fileExtension = os.get(classOf[String], "extension", ".bin")
     val generateBbcMicroInfFile = os.get(classOf[Boolean], "bbc_inf", false)
+    val generateGameBoyChecksums = os.get(classOf[Boolean], "gb_checksum", false)
     val outputStyle = os.get(classOf[String], "style", "single") match {
       case "" | "single" => OutputStyle.Single
       case "per_bank" | "per_segment" => OutputStyle.PerBank
@@ -227,6 +229,7 @@ object Platform {
       freePointers,
       if (fileExtension == "" || fileExtension.startsWith(".")) fileExtension else "." + fileExtension,
       generateBbcMicroInfFile,
+      generateGameBoyChecksums,
       bankNumbers,
       defaultCodeBank,
       outputStyle)

src/test/scala/millfork/test/emu/EmuPlatform.scala

@@ -26,6 +26,7 @@ object EmuPlatform {
     pointers,
     ".bin",
     false,
+    false,
     Map("default" -> 0),
     "default",
     OutputStyle.Single