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mGBA Game Boy Advance Emulator

ARM: Fix Addressing mode 1 shifter on rs == pc (fixes #1926)
Vicki Pfau vi@endrift.com
Sun, 01 Nov 2020 02:22:09 -0800
commit

9c321c30c2b5d0d5c0ca43a21e308361937e2580

parent

17f0edd7862b2f02dac4f323e3afee6853dbd891

2 files changed, 8 insertions(+), 20 deletions(-)

jump to
M CHANGES → CHANGES 
@@ -1,3 +1,7 @@
+0.8.5: (Future)
+Emulation fixes:
+ - ARM: Fix Addressing mode 1 shifter on rs == pc (fixes mgba.io/i/1926)
+
 0.8.4: (2020-10-29)
 Emulation fixes:
  - GB Audio: Fix initial sweep state
M src/arm/isa-arm.c → src/arm/isa-arm.c 
@@ -19,15 +19,11 @@ int rm = opcode & 0x0000000F;
 	if (opcode & 0x00000010) {
 		int rs = (opcode >> 8) & 0x0000000F;
 		++cpu->cycles;
-		int shift = cpu->gprs[rs];
-		if (rs == ARM_PC) {
-			shift += 4;
-		}
-		shift &= 0xFF;
 		int32_t shiftVal = cpu->gprs[rm];
 		if (rm == ARM_PC) {
 			shiftVal += 4;
 		}
+		int shift = cpu->gprs[rs] & 0xFF;
 		if (!shift) {
 			cpu->shifterOperand = shiftVal;
 			cpu->shifterCarryOut = cpu->cpsr.c;

@@ -58,15 +54,11 @@ int rm = opcode & 0x0000000F;
 	if (opcode & 0x00000010) {
 		int rs = (opcode >> 8) & 0x0000000F;
 		++cpu->cycles;
-		int shift = cpu->gprs[rs];
-		if (rs == ARM_PC) {
-			shift += 4;
-		}
-		shift &= 0xFF;
 		uint32_t shiftVal = cpu->gprs[rm];
 		if (rm == ARM_PC) {
 			shiftVal += 4;
 		}
+		int shift = cpu->gprs[rs] & 0xFF;
 		if (!shift) {
 			cpu->shifterOperand = shiftVal;
 			cpu->shifterCarryOut = cpu->cpsr.c;

@@ -97,15 +89,11 @@ int rm = opcode & 0x0000000F;
 	if (opcode & 0x00000010) {
 		int rs = (opcode >> 8) & 0x0000000F;
 		++cpu->cycles;
-		int shift = cpu->gprs[rs];
-		if (rs == ARM_PC) {
-			shift += 4;
-		}
-		shift &= 0xFF;
 		int shiftVal =  cpu->gprs[rm];
 		if (rm == ARM_PC) {
 			shiftVal += 4;
 		}
+		int shift = cpu->gprs[rs] & 0xFF;
 		if (!shift) {
 			cpu->shifterOperand = shiftVal;
 			cpu->shifterCarryOut = cpu->cpsr.c;

@@ -136,15 +124,11 @@ int rm = opcode & 0x0000000F;
 	if (opcode & 0x00000010) {
 		int rs = (opcode >> 8) & 0x0000000F;
 		++cpu->cycles;
-		int shift = cpu->gprs[rs];
-		if (rs == ARM_PC) {
-			shift += 4;
-		}
-		shift &= 0xFF;
 		int shiftVal =  cpu->gprs[rm];
 		if (rm == ARM_PC) {
 			shiftVal += 4;
 		}
+		int shift = cpu->gprs[rs] & 0xFF;
 		int rotate = shift & 0x1F;
 		if (!shift) {
 			cpu->shifterOperand = shiftVal;