if (doGPUDis)
WriteLog("%06X: DIV R%02u, R%02u (%s) [NCZ:%u%u%u, R%02u=%08X, R%02u=%08X] -> ", gpu_pc-2, IMM_1, IMM_2, (gpu_div_control & 0x01 ? "16.16" : "32"), gpu_flag_n, gpu_flag_c, gpu_flag_z, IMM_1, RM, IMM_2, RN);
#endif
-// NOTE: remainder is NOT calculated correctly here!
-// The original tried to get it right by checking to see if the
-// remainder was negative, but that's too late...
-// The code there should do it now, but I'm not 100% sure...
-// [Now it should be correct, but not displaying correct behavior of the actual
-// hardware. A step in the right direction.]
-
+#if 0
if (RM)
{
if (gpu_div_control & 0x01) // 16.16 division
gpu_remain = RN % RM;
RN = RN / RM;
}
-
-// What we really should do here is figure out why this condition
-// happens in the real divide unit and emulate *that* behavior.
-#if 0
- if ((gpu_remain - RM) & 0x80000000) // If the result would have been negative...
- gpu_remain -= RM; // Then make it negative!
-#endif
}
else
+ {
+ // This is what happens according to SCPCD. NYAN!
RN = 0xFFFFFFFF;
+ gpu_remain = 0;
+ }
+#else
+ // Real algorithm, courtesy of SCPCD: NYAN!
+ uint32_t q = RN;
+ uint32_t r = 0;
+
+ // If 16.16 division, stuff top 16 bits of RN into remainder and put the
+ // bottom 16 of RN in top 16 of quotient
+ if (gpu_div_control & 0x01)
+ q <<= 16, r = RN >> 16;
+
+ for(int i=0; i<32; i++)
+ {
+// uint32_t sign = (r >> 31) & 0x01;
+ uint32_t sign = r & 0x80000000;
+ r = (r << 1) | ((q >> 31) & 0x01);
+ r += (sign ? RM : -RM);
+ q = (q << 1) | (((~r) >> 31) & 0x01);
+ }
+
+ RN = q;
+ gpu_remain = r;
+#endif
#ifdef GPU_DIS_DIV
if (doGPUDis)