sim: bugfix for overflow and so ...

[calu.git] / 3b_sim / ccpu.cpp

diff --git a/3b_sim/ccpu.cpp b/3b_sim/ccpu.cpp
index 04dd5951b4021e13ac62a86bbd28f390a6af2983..abeeafd607c912e01402a9d889871895fe6bee49 100644 (file)
--- a/3b_sim/ccpu.cpp
+++ b/3b_sim/ccpu.cpp
@@ -127,8 +127,10 @@ void CCpu::updateFlags(CDatd val, CDat a, CDat b) {
        this->m_Z = (val == 0);
        this->m_S = ((val >> (BIT_LEN-1)) & 0x1);
        this->m_C = ((val >> (BIT_LEN)) & 0x1);
-       bool v = (((a ^ b) >> (BIT_LEN-1)) & 0x1) ? true : false;
-       this->m_O = (this->m_S != v);
+       bool a_31 = ((a >> (BIT_LEN-1)) & 0x1);
+       bool b_31 = ((b >> (BIT_LEN-1)) & 0x1);
+       bool val_31 = ((val >> (BIT_LEN-1)) & 0x1);
+       this->m_O = ((a_31 && b_31 && !val_31) || (!a_31 && !b_31 && val_31));
 }
 
 void CCpu::updateCarry(bool c)