Revert "move x86 popcount.h implementations to util/arch/x86/popcount.h"

This reverts commit 6581aae.
VectorCamp · Sep 24, 2020 · 04fbf24 · 04fbf24
1 parent 5333467
commit 04fbf24
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Showing 3 changed files with 27 additions and 135 deletions.
diff --git a/src/util/arch/common/popcount.h b/src/util/arch/common/popcount.h
diff --git a/src/util/arch/x86/popcount.h b/src/util/arch/x86/popcount.h
diff --git a/src/util/popcount.h b/src/util/popcount.h
@@ -33,22 +33,41 @@
 #ifndef UTIL_POPCOUNT_H_
 #define UTIL_POPCOUNT_H_
 
-#include "config.h"
 #include "ue2common.h"
 #include "util/arch.h"
 
-#if defined(ARCH_IA32) || defined(ARCH_X86_64)
-#include "util/arch/x86/popcount.h"
-#endif
-
 static really_inline
 u32 popcount32(u32 x) {
-    return popcount32_impl(x);
+#if defined(HAVE_POPCOUNT_INSTR)
+    // Single-instruction builtin.
+    return _mm_popcnt_u32(x);
+#else
+    // Fast branch-free version from bit-twiddling hacks as older Intel
+    // processors do not have a POPCNT instruction.
+    x -= (x >> 1) & 0x55555555;
+    x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
+    return (((x + (x >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
+#endif
 }
 
 static really_inline
-u32 popcount64(u32 x) {
-    return popcount64_impl(x);
+u32 popcount64(u64a x) {
+#if defined(ARCH_X86_64)
+# if defined(HAVE_POPCOUNT_INSTR)
+    // Single-instruction builtin.
+    return (u32)_mm_popcnt_u64(x);
+# else
+    // Fast branch-free version from bit-twiddling hacks as older Intel
+    // processors do not have a POPCNT instruction.
+    x -= (x >> 1) & 0x5555555555555555;
+    x = (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333);
+    x = (x + (x >> 4)) & 0x0f0f0f0f0f0f0f0f;
+    return (x * 0x0101010101010101) >> 56;
+# endif
+#else
+    // Synthesise from two 32-bit cases.
+    return popcount32(x >> 32) + popcount32(x);
+#endif
 }
 
 #endif /* UTIL_POPCOUNT_H_ */