cpu: fix error in shift opcodes

PatchMixolydic · Jan 21, 2018 · 9914796 · 9914796
1 parent 642132f
commit 9914796
Showing 1 changed file with 4 additions and 4 deletions.
diff --git a/src/Chip8.cpp b/src/Chip8.cpp
@@ -110,16 +110,16 @@ void Chip8::step() {
         state.v[x(opcode)] -= state.v[y(opcode)];
     } else if (opidx(opcode) == 0x8 && nibble(opcode) == 0x6) {
         // If the least-significant bit of Vx is 1, then VF is set to 1, otherwise 0. Then Vx is divided by 2.
-        state.v[0xF] = state.v[x(opcode)] & 1;
-        state.v[x(opcode)] >>= 1;
+        state.v[0xF] = state.v[y(opcode)] & 1;
+        state.v[x(opcode)] = state.v[y(opcode)] >> 1;
     } else if (opidx(opcode) == 0x8 && nibble(opcode) == 0x7) {
         // sub Vx from Vy and store result in Vx, VF is 1 if Vy > Vx
         state.v[0xF] = state.v[y(opcode)] > state.v[x(opcode)];
         state.v[x(opcode)] = state.v[y(opcode)] - state.v[x(opcode)];
     } else if (opidx(opcode) == 0x8 && nibble(opcode) == 0x6) {
         // If the most-significant bit of Vx is 1, then VF is set to 1, otherwise to 0. Then Vx is multiplied by 2.
-        state.v[0xF] = (state.v[x(opcode)] & 0b10000000) >> 7;
-        state.v[x(opcode)] <<= 1;
+        state.v[0xF] = (state.v[y(opcode)] & 0b10000000) >> 7;
+        state.v[x(opcode)] = state.v[y(opcode)] << 1;
     } else if (opidx(opcode) == 0x9 && nibble(opcode) == 0x0) {
         // Skip next instruction if Vx != Vy
         if (state.v[x(opcode)] != state.v[y(opcode)]) {