Create a Math.h utility. Use it for count leading sign bits, used in MMI.

common/include/Utilities/Math.h

@@ -0,0 +1,41 @@
+/*  PCSX2 - PS2 Emulator for PCs
+ *  Copyright (C) 2014-  PCSX2 Dev Team
+ *
+ *  PCSX2 is free software: you can redistribute it and/or modify it under the terms
+ *  of the GNU Lesser General Public License as published by the Free Software Found-
+ *  ation, either version 3 of the License, or (at your option) any later version.
+ *
+ *  PCSX2 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ *  PURPOSE.  See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with PCSX2.
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+// Hopefully this file will be used for cross-source math utilities.
+// Currently these are strewn across the code base. Please collect them all!
+
+#include "Pcsx2Defs.h"
+
+// On GCC >= 4.7, this is equivalent to __builtin_clrsb(n);
+inline u32 count_leading_sign_bits(s32 n) {
+	// If BSR is used directly, it would have an undefined value for 0.
+	if (n == 0)
+		return 32;
+
+	// If the sign bit is 1, we invert the bits to 0 for count-leading-zero.
+	if (n < 0)
+		n = ~n;
+
+	// Perform our count leading zero.
+#ifdef _MSC_VER
+	unsigned long ret;
+	_BitScanReverse(&ret, n);
+	return 31 - (u32)ret;
+#else
+	return __builtin_clz(n); 
+#endif
+}
+

pcsx2/MMI.cpp

@@ -16,6 +16,7 @@
 
 #include "PrecompiledHeader.h"
 #include "Common.h"
+#include "Utilities/Math.h"
 
 namespace R5900 {
 namespace Interpreter {
@@ -145,30 +146,13 @@ namespace MMI {
 
 //*****************MMI OPCODES*********************************
 
-static __fi void _PLZCW(int n)
-{
-	// This function counts the number of "like" bits in the source register, starting
-	// with the MSB and working its way down, and returns the result MINUS ONE.
-	// So 0xff00 would return 7, not 8.
-
-	int c = 0;
-	s32 i = cpuRegs.GPR.r[_Rs_].SL[n];
-
-	// Negate the source based on the sign bit.  This allows us to use a simple
-	// unified bit test of the MSB for either condition.
-	if( i >= 0 ) i = ~i;
-
-	// shift first, compare, then increment.  This excludes the sign bit from our final count.
-	while( i <<= 1, i < 0 ) c++;
-
-	cpuRegs.GPR.r[_Rd_].UL[n] = c;
-}
-
 void PLZCW() {
-    if (!_Rd_) return;
+	if (!_Rd_)
+		return;
 
-	_PLZCW (0);
-	_PLZCW (1);
+	// Return the leading sign bits, excluding the original bit
+	cpuRegs.GPR.r[_Rd_].UL[0] = count_leading_sign_bits(cpuRegs.GPR.r[_Rs_].SL[0]) - 1;
+	cpuRegs.GPR.r[_Rd_].UL[1] = count_leading_sign_bits(cpuRegs.GPR.r[_Rs_].SL[1]) - 1;
 }
 
 __fi void PMFHL_CLAMP(u16& dst, s32 src)

pcsx2/x86/iMMI.cpp

@@ -25,6 +25,7 @@
 #include "R5900OpcodeTables.h"
 #include "iR5900.h"
 #include "iMMI.h"
+#include "Utilities/Math.h"
 
 using namespace x86Emitter;
 
@@ -66,23 +67,10 @@ void recPLZCW()
 		_deleteEEreg(_Rd_, 0);
 		GPR_SET_CONST(_Rd_);
 
-		for(regs = 0; regs < 2; ++regs) {
-			u32 val = g_cpuConstRegs[_Rs_].UL[regs];
+		// Return the leading sign bits, excluding the original bit
+		g_cpuConstRegs[_Rd_].UL[0] = count_leading_sign_bits(g_cpuConstRegs[_Rs_].SL[0]) - 1;
+		g_cpuConstRegs[_Rd_].UL[1] = count_leading_sign_bits(g_cpuConstRegs[_Rs_].SL[1]) - 1;
 
-			if( val != 0 ) {
-				u32 setbit = val&0x80000000;
-				g_cpuConstRegs[_Rd_].UL[regs] = 0;
-				val <<= 1;
-
-				while((val & 0x80000000) == setbit) {
-					g_cpuConstRegs[_Rd_].UL[regs]++;
-					val <<= 1;
-				}
-			}
-			else {
-				g_cpuConstRegs[_Rd_].UL[regs] = 31;
-			}
-		}
 		return;
 	}