GBA Memory: Fix prefetch mask when swapping modes within a region

CHANGES

@@ -11,6 +11,7 @@ Emulation fixes:
  - GBA SIO: Add missing NORMAL8 implementation bits (fixes mgba.io/i/2172)
  - GBA SIO: Fix missing interrupt on an unattached NORMAL transfer
  - GBA SIO: Fix SI value for unattached MULTI mode
+ - GBA Memory: Fix prefetch mask when swapping modes within a region
  - GBA Video: Revert scanline latching changes (fixes mgba.io/i/2153, mgba.io/i/2149)
 Other fixes:
  - 3DS: Fix disabling "wide" mode on 2DS (fixes mgba.io/i/2167)

src/gba/memory.c

@@ -127,6 +127,7 @@ void GBAMemoryReset(struct GBA* gba) {
 	memset(gba->memory.io, 0, sizeof(gba->memory.io));
 	GBAAdjustWaitstates(gba, 0);
 
+	gba->memory.activeRegion = -1;
 	gba->memory.agbPrintProtect = 0;
 	gba->memory.agbPrintBase = 0;
 	memset(&gba->memory.agbPrintCtx, 0, sizeof(gba->memory.agbPrintCtx));
@@ -266,6 +267,11 @@ static void GBASetActiveRegion(struct ARMCore* cpu, uint32_t address) {
 	gba->lastJump = address;
 	memory->lastPrefetchedPc = 0;
 	if (newRegion == memory->activeRegion) {
+		if (cpu->cpsr.t) {
+			cpu->memory.activeMask |= WORD_SIZE_THUMB;
+		} else {
+			cpu->memory.activeMask &= -WORD_SIZE_ARM;
+		}
 		if (newRegion < REGION_CART0 || (address & (SIZE_CART0 - 1)) < memory->romSize) {
 			return;
 		}

src/gba/serialize.c

@@ -158,6 +158,7 @@ bool GBADeserialize(struct GBA* gba, const struct GBASerializedState* state) {
 		mLOG(GBA_STATE, WARN, "Savestate has unaligned PC and is probably corrupted");
 		gba->cpu->gprs[ARM_PC] &= ~1;
 	}
+	gba->memory.activeRegion = -1;
 	gba->cpu->memory.setActiveRegion(gba->cpu, gba->cpu->gprs[ARM_PC]);
 	if (state->biosPrefetch) {
 		LOAD_32(gba->memory.biosPrefetch, 0, &state->biosPrefetch);