gte: more modern lzc for interpreter

diff --git a/libpcsxcore/gte.c b/libpcsxcore/gte.c
index dde3df8..6e121bc 100644 (file)
--- a/libpcsxcore/gte.c
+++ b/libpcsxcore/gte.c
@@ -25,6 +25,7 @@
 
 #include "gte.h"
 #include "psxmem.h"
+#include "../include/compiler_features.h"
 
 #define VX(n) (n < 3 ? regs->CP2D.p[n << 1].sw.l : regs->CP2D.p[9].sw.l)
 #define VY(n) (n < 3 ? regs->CP2D.p[n << 1].sw.h : regs->CP2D.p[10].sw.l)
@@ -335,6 +336,16 @@ u32 MFC2(struct psxCP2Regs *regs, int reg) {
        return regs->CP2D.r[reg];
 }
 
+static u32 lzc(s32 val)
+{
+#if __has_builtin(__builtin_clrsb)
+       return 1 + __builtin_clrsb(val);
+#else
+       val ^= val >> 31;
+       return val ? __builtin_clz(val) : 32;
+#endif
+}
+
 void MTC2(struct psxCP2Regs *regs, u32 value, int reg) {
        switch (reg) {
                case 15:
@@ -353,24 +364,8 @@ void MTC2(struct psxCP2Regs *regs, u32 value, int reg) {
                        break;
 
                case 30:
-                       {
-                               int a;
-                               gteLZCS = value;
-
-                               a = gteLZCS;
-                               if (a > 0) {
-                                       int i;
-                                       for (i = 31; (a & (1u << i)) == 0 && i >= 0; i--);
-                                       gteLZCR = 31 - i;
-                               } else if (a < 0) {
-                                       int i;
-                                       a ^= 0xffffffff;
-                                       for (i = 31; (a & (1u << i)) == 0 && i >= 0; i--);
-                                       gteLZCR = 31 - i;
-                               } else {
-                                       gteLZCR = 32;
-                               }
-                       }
+                       gteLZCS = value;
+                       gteLZCR = lzc(value);
                        break;
 
                case 31: