1 files changed, 48 insertions, 5 deletions
diff --git a/libvpx/vp9/common/vp9_systemdependent.h b/libvpx/vp9/common/vp9_systemdependent.h
index 254a431..e971158 100644
--- a/libvpx/vp9/common/vp9_systemdependent.h
+++ b/libvpx/vp9/common/vp9_systemdependent.h
@@ -12,8 +12,16 @@
 #define VP9_COMMON_VP9_SYSTEMDEPENDENT_H_
 
 #ifdef _MSC_VER
-#include <math.h>
-#define snprintf _snprintf
+# include <math.h>  // the ceil() definition must precede intrin.h
+# if _MSC_VER > 1310 && (defined(_M_X64) || defined(_M_IX86))
+#  include <intrin.h>
+#  define USE_MSC_INTRIN
+# endif
+# define snprintf _snprintf
+#endif
+
+#ifdef __cplusplus
+extern "C" {
 #endif
 
 #include "./vpx_config.h"
@@ -26,7 +34,7 @@ void vpx_reset_mmx_state(void);
 
 #if defined(_MSC_VER) && _MSC_VER < 1800
 // round is not defined in MSVC before VS2013.
-static int round(double x) {
+static INLINE int round(double x) {
   if (x < 0)
     return (int)ceil(x - 0.5);
   else
@@ -34,7 +42,42 @@ static int round(double x) {
 }
 #endif
 
-struct VP9Common;
-void vp9_machine_specific_config(struct VP9Common *cm);
+// use GNU builtins where available.
+#if defined(__GNUC__) && \
+    ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4)
+static INLINE int get_msb(unsigned int n) {
+  return 31 ^ __builtin_clz(n);
+}
+#elif defined(USE_MSC_INTRIN)
+#pragma intrinsic(_BitScanReverse)
+
+static INLINE int get_msb(unsigned int n) {
+  unsigned long first_set_bit;
+  _BitScanReverse(&first_set_bit, n);
+  return first_set_bit;
+}
+#undef USE_MSC_INTRIN
+#else
+// Returns (int)floor(log2(n)). n must be > 0.
+static INLINE int get_msb(unsigned int n) {
+  int log = 0;
+  unsigned int value = n;
+  int i;
+
+  for (i = 4; i >= 0; --i) {
+    const int shift = (1 << i);
+    const unsigned int x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  return log;
+}
+#endif
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
 
 #endif  // VP9_COMMON_VP9_SYSTEMDEPENDENT_H_