From f0d3237c320fb4b3e5d9d05c7182f33fdca7abe6 Mon Sep 17 00:00:00 2001
From: costan <costan@google.com>
Date: Tue, 1 Aug 2017 10:01:27 -0700
Subject: [PATCH] Use _BitScanForward and _BitScanReverse on MSVC.

Based on https://github.com/google/snappy/pull/30
---
 snappy-stubs-internal.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/snappy-stubs-internal.h b/snappy-stubs-internal.h
index 881f7ad..841e4a0 100644
--- a/snappy-stubs-internal.h
+++ b/snappy-stubs-internal.h
@@ -45,6 +45,10 @@
 #include <sys/mman.h>
 #endif
 
+#if defined(_MSC_VER)
+#include <intrin.h>
+#endif  // defined(_MSC_VER)
+
 #include "snappy-stubs-public.h"
 
 #if defined(__x86_64__)
@@ -347,7 +351,10 @@ class Bits {
   // undefined value if n == 0.  FindLSBSetNonZero() is similar to ffs() except
   // that it's 0-indexed.
   static int FindLSBSetNonZero(uint32 n);
+
+#if defined(ARCH_K8) || defined(ARCH_PPC)
   static int FindLSBSetNonZero64(uint64 n);
+#endif  // defined(ARCH_K8) || defined(ARCH_PPC)
 
  private:
   // No copying
@@ -365,9 +372,36 @@ inline int Bits::FindLSBSetNonZero(uint32 n) {
   return __builtin_ctz(n);
 }
 
+#if defined(ARCH_K8) || defined(ARCH_PPC)
 inline int Bits::FindLSBSetNonZero64(uint64 n) {
   return __builtin_ctzll(n);
 }
+#endif  // defined(ARCH_K8) || defined(ARCH_PPC)
+
+#elif defined(_MSC_VER)
+
+inline int Bits::Log2Floor(uint32 n) {
+  unsigned long where;
+  if (_BitScanReverse(&where, n)) {
+    return where;
+  } else {
+    return -1;
+  }
+}
+
+inline int Bits::FindLSBSetNonZero(uint32 n) {
+  unsigned long where;
+  if (_BitScanForward(&where, n)) return static_cast<int>(where);
+  return 32;
+}
+
+#if defined(ARCH_K8) || defined(ARCH_PPC)
+inline int Bits::FindLSBSetNonZero64(uint64 n) {
+  unsigned long where;
+  if (_BitScanForward64(&where, n)) return static_cast<int>(where);
+  return 64;
+}
+#endif  // defined(ARCH_K8) || defined(ARCH_PPC)
 
 #else  // Portable versions.
 
@@ -401,6 +435,7 @@ inline int Bits::FindLSBSetNonZero(uint32 n) {
   return rc;
 }
 
+#if defined(ARCH_K8) || defined(ARCH_PPC)
 // FindLSBSetNonZero64() is defined in terms of FindLSBSetNonZero().
 inline int Bits::FindLSBSetNonZero64(uint64 n) {
   const uint32 bottombits = static_cast<uint32>(n);
@@ -411,6 +446,7 @@ inline int Bits::FindLSBSetNonZero64(uint64 n) {
     return FindLSBSetNonZero(bottombits);
   }
 }
+#endif  // defined(ARCH_K8) || defined(ARCH_PPC)
 
 #endif  // End portable versions.