qemu/host-utils.h: Reduce the operation count in the fallback ctpop

Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Richard Henderson <rth@twiddle.net>
qemu · Jan 10, 2017 · 7bdcecb · 7bdcecb
1 parent 4885c3c
commit 7bdcecb
Showing 1 changed file with 11 additions and 14 deletions.
diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
@@ -327,7 +327,7 @@ static inline int ctpop8(uint8_t val)
 #else
     val = (val & 0x55) + ((val >> 1) & 0x55);
     val = (val & 0x33) + ((val >> 2) & 0x33);
-    val = (val & 0x0f) + ((val >> 4) & 0x0f);
+    val = (val + (val >> 4)) & 0x0f;
 
     return val;
 #endif
@@ -344,8 +344,8 @@ static inline int ctpop16(uint16_t val)
 #else
     val = (val & 0x5555) + ((val >> 1) & 0x5555);
     val = (val & 0x3333) + ((val >> 2) & 0x3333);
-    val = (val & 0x0f0f) + ((val >> 4) & 0x0f0f);
-    val = (val & 0x00ff) + ((val >> 8) & 0x00ff);
+    val = (val + (val >> 4)) & 0x0f0f;
+    val = (val + (val >> 8)) & 0x00ff;
 
     return val;
 #endif
@@ -360,11 +360,10 @@ static inline int ctpop32(uint32_t val)
 #if QEMU_GNUC_PREREQ(3, 4)
     return __builtin_popcount(val);
 #else
-    val = (val & 0x55555555) + ((val >>  1) & 0x55555555);
-    val = (val & 0x33333333) + ((val >>  2) & 0x33333333);
-    val = (val & 0x0f0f0f0f) + ((val >>  4) & 0x0f0f0f0f);
-    val = (val & 0x00ff00ff) + ((val >>  8) & 0x00ff00ff);
-    val = (val & 0x0000ffff) + ((val >> 16) & 0x0000ffff);
+    val = (val & 0x55555555) + ((val >> 1) & 0x55555555);
+    val = (val & 0x33333333) + ((val >> 2) & 0x33333333);
+    val = (val + (val >> 4)) & 0x0f0f0f0f;
+    val = (val * 0x01010101) >> 24;
 
     return val;
 #endif
@@ -379,12 +378,10 @@ static inline int ctpop64(uint64_t val)
 #if QEMU_GNUC_PREREQ(3, 4)
     return __builtin_popcountll(val);
 #else
-    val = (val & 0x5555555555555555ULL) + ((val >>  1) & 0x5555555555555555ULL);
-    val = (val & 0x3333333333333333ULL) + ((val >>  2) & 0x3333333333333333ULL);
-    val = (val & 0x0f0f0f0f0f0f0f0fULL) + ((val >>  4) & 0x0f0f0f0f0f0f0f0fULL);
-    val = (val & 0x00ff00ff00ff00ffULL) + ((val >>  8) & 0x00ff00ff00ff00ffULL);
-    val = (val & 0x0000ffff0000ffffULL) + ((val >> 16) & 0x0000ffff0000ffffULL);
-    val = (val & 0x00000000ffffffffULL) + ((val >> 32) & 0x00000000ffffffffULL);
+    val = (val & 0x5555555555555555ULL) + ((val >> 1) & 0x5555555555555555ULL);
+    val = (val & 0x3333333333333333ULL) + ((val >> 2) & 0x3333333333333333ULL);
+    val = (val + (val >> 4)) & 0x0f0f0f0f0f0f0f0fULL;
+    val = (val * 0x0101010101010101ULL) >> 56;
 
     return val;
 #endif