vdp: fix read auto-increment wrapping

We did not mask the incremented address value properly, so the read
address pointer wrapped at 1024 instead of 16384.

This is what caused the map bug in the Sonic intro screen.

Add test for read wrapping and one specifically for this bug.

Author: anisse

src/vdp.rs

@@ -782,7 +782,7 @@ impl VdpState {
         }
         let val = self.vram_buffer;
         self.vram_buffer = self.vram[self.addr as usize];
-        self.addr = (self.addr + 1) & 0x3FF;
+        self.addr = (self.addr + 1) & 0x3FFF;
 
         Ok(val)
     }
@@ -1179,3 +1179,52 @@ fn split_io() {
     assert_eq!(vdp.input(VDP_DATA), Ok(0xB2));
     assert_eq!(vdp.input(VDP_DATA), Ok(0xC3));
 }
+
+#[test]
+fn read_wrap() {
+    use crate::io::Device;
+    let vdp = Vdp::default();
+
+    // write some data first
+    assert_eq!(vdp.out(VDP_CMD, 0xFE), Ok(()));
+    assert_eq!(vdp.out(VDP_CMD, 0x7F), Ok(()));
+
+    assert_eq!(vdp.out(VDP_DATA, 0xA1), Ok(()));
+    assert_eq!(vdp.out(VDP_DATA, 0xB2), Ok(()));
+
+    // address 0 (we are not testing write wrapping)
+    assert_eq!(vdp.out(VDP_CMD, 0), Ok(()));
+    assert_eq!(vdp.out(VDP_CMD, 0x40), Ok(()));
+
+    assert_eq!(vdp.out(VDP_DATA, 0xC3), Ok(()));
+    assert_eq!(vdp.out(VDP_DATA, 0xD4), Ok(()));
+
+    // read the data
+    assert_eq!(vdp.out(VDP_CMD, 0xFE), Ok(()));
+    assert_eq!(vdp.out(VDP_CMD, 0x3F), Ok(()));
+
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xA1));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xB2));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xC3));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xD4));
+
+    // Now the bug we had: we don't want wrapping at 1024
+    let vdp = Vdp::default();
+    // write some data first
+    assert_eq!(vdp.out(VDP_CMD, 0xFE), Ok(()));
+    assert_eq!(vdp.out(VDP_CMD, 0x43), Ok(()));
+
+    assert_eq!(vdp.out(VDP_DATA, 0xA1), Ok(()));
+    assert_eq!(vdp.out(VDP_DATA, 0xB2), Ok(()));
+    assert_eq!(vdp.out(VDP_DATA, 0xC3), Ok(()));
+    assert_eq!(vdp.out(VDP_DATA, 0xD4), Ok(()));
+
+    // read the data
+    assert_eq!(vdp.out(VDP_CMD, 0xFE), Ok(()));
+    assert_eq!(vdp.out(VDP_CMD, 0x03), Ok(()));
+
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xA1));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xB2));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xC3));
+    assert_eq!(vdp.input(VDP_DATA), Ok(0xD4));
+}