From 3bc815a5dc18a646334ba933c74ce7ce44099625 Mon Sep 17 00:00:00 2001
From: Fernando Sahmkow <fsahmkow27@gmail.com>
Date: Fri, 15 Mar 2019 23:18:11 -0400
Subject: Implement intrinsics CountTrailingZeroes and test it.

---
 src/common/bit_util.h | 45 +++++++++++++++++++++++++++++++++------------
 1 file changed, 33 insertions(+), 12 deletions(-)

(limited to 'src/common/bit_util.h')

diff --git a/src/common/bit_util.h b/src/common/bit_util.h
index 14e53c273..70e728a5e 100644
--- a/src/common/bit_util.h
+++ b/src/common/bit_util.h
@@ -59,22 +59,43 @@ inline u64 CountLeadingZeroes64(u64 value) {
 }
 #endif
 
+
+#ifdef _MSC_VER
 inline u32 CountTrailingZeroes32(u32 value) {
-  u32 count = 0;
-  while (((value >> count) & 0xf) == 0 && count < 32)
-    count += 4;
-  while (((value >> count) & 1) == 0 && count < 32)
-    count++;
-  return count;
+    unsigned long trailing_zero = 0;
+
+    if (_BitScanForward(&trailing_zero, value) != 0) {
+        return trailing_zero;
+    }
+
+    return 32;
 }
 
 inline u64 CountTrailingZeroes64(u64 value) {
-  u64 count = 0;
-  while (((value >> count) & 0xf) == 0 && count < 64)
-    count += 4;
-  while (((value >> count) & 1) == 0 && count < 64)
-    count++;
-  return count;
+    unsigned long trailing_zero = 0;
+
+    if (_BitScanForward64(&trailing_zero, value) != 0) {
+        return trailing_zero;
+    }
+
+    return 64;
 }
+#else
+inline u32 CountTrailingZeroes32(u32 value) {
+    if (value == 0) {
+        return 32;
+    }
+
+    return __builtin_ctz(value);
+}
+
+inline u64 CountTrailingZeroes64(u64 value) {
+    if (value == 0) {
+        return 64;
+    }
+
+    return __builtin_ctzll(value);
+}
+#endif
 
 } // namespace Common
-- 
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