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Use _BitScanReverse for EC_ILOG with MSVC.

Also updates the TI dsplib macros to use the same EC_CLZ mechanism
 as everything else.

--- a/libcelt/ecintrin.h

+++ b/libcelt/ecintrin.h

@@ -83,17 +83,30 @@

 /*Count leading zeros.

   This macro should only be used for implementing ec_ilog(), if it is defined.

   All other code should use EC_ILOG() instead.*/

-#ifdef __GNUC_PREREQ

-#if __GNUC_PREREQ(3,4)

-# if INT_MAX>=2147483647

-#  define EC_CLZ0 sizeof(unsigned)*CHAR_BIT

-#  define EC_CLZ(_x) (__builtin_clz(_x))

-# elif LONG_MAX>=2147483647L

-#  define EC_CLZ0 sizeof(unsigned long)*CHAR_BIT

-#  define EC_CLZ(_x) (__builtin_clzl(_x))

+#if defined(_MSC_VER)

+# include <intrin.h>

+static __inline int ec_bsr(unsigned long _x){

+  unsigned long ret;

+  _BitScanReverse(&ret,_x);

+  return (int)ret;

+}

+# define EC_CLZ0    (1)

+# define EC_CLZ(_x) (-ec_bsr(_x))

+#elif defined(ENABLE_TI_DSPLIB)

+# include "dsplib.h"

+# define EC_CLZ0    (31)

+# define EC_CLZ(_x) (_lnorm(x))

+#elif defined(__GNUC_PREREQ)

+# if __GNUC_PREREQ(3,4)

+#  if INT_MAX>=2147483647

+#   define EC_CLZ0    ((int)sizeof(unsigned)*CHAR_BIT)

+#   define EC_CLZ(_x) (__builtin_clz(_x))

+#  elif LONG_MAX>=2147483647L

+#   define EC_CLZ0    ((int)sizeof(unsigned long)*CHAR_BIT)

+#   define EC_CLZ(_x) (__builtin_clzl(_x))

+#  endif

 # endif

 #endif

-#endif

 #if defined(EC_CLZ)

 /*Note that __builtin_clz is not defined when _x==0, according to the gcc

@@ -101,9 +114,6 @@

   The majority of the time we can never pass it zero.

   When we need to, it can be special cased.*/

 # define EC_ILOG(_x) (EC_CLZ0-EC_CLZ(_x))

-#elif defined(ENABLE_TI_DSPLIB)

-#include "dsplib.h"

-#define EC_ILOG(x) (31 - _lnorm(x))

 #else

 # define EC_ILOG(_x) (ec_ilog(_x))

 #endif