How to use MSVC intrinsics to get the equivalent of this GCC code?

Question

The following code calls the builtin functions for clz/ctz in GCC and, on other systems, has C versions. Obviously, the C versions are a bit suboptimal if the system has a

Answer 1

There are two intrinsics "_BitScanForward" and "_BitScanReverse", which suits the same purpose for MSVC. Include . The functions are:

#ifdef _MSC_VER
#include 

static uint32_t __inline ctz( uint32_t x )
{
   int r = 0;
   _BitScanReverse(&r, x);
   return r;
}

static uint32_t __inline clz( uint32_t x )
{
   int r = 0;
   _BitScanForward(&r, x);
   return r;
}
#endif

There are equivalent 64bit versions "_BitScanForward64" and "_BitScanReverse64".

Read more here:

x86 Intrinsics on MSDN