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 builtin clz/ctz instruction, like x86 and ARM.

#ifdef __GNUC__
#define clz(x) __builtin_clz(x)
#define ctz(x) __builtin_ctz(x)
#else
static uint32_t ALWAYS_INLINE popcnt( uint32_t x )
{
    x -= ((x >> 1) & 0x55555555);
    x = (((x >> 2) & 0x33333333) + (x & 0x33333333));
    x = (((x >> 4) + x) & 0x0f0f0f0f);
    x += (x >> 8);
    x += (x >> 16);
    return x & 0x0000003f;
}
static uint32_t ALWAYS_INLINE clz( uint32_t x )
{
    x |= (x >> 1);
    x |= (x >> 2);
    x |= (x >> 4);
    x |= (x >> 8);
    x |= (x >> 16);
    return 32 - popcnt(x);
}
static uint32_t ALWAYS_INLINE ctz( uint32_t x )
{
    return popcnt((x & -x) - 1);
}

#endif

What functions do I need to call, which headers do I need to include, etc to add a proper ifdef for MSVC here? I've already looked at this page, but I'm not entirely sure what the #pragma is for (is it required?) and what restrictions it puts on MSVC version requirements for compilation. As someone who doesn't really use MSVC, I also don't know whether these intrinsics have C equivalents on other architectures, or whether I have to #ifdef x86/x86_64 as well when #defining them.

Answer 1

If MSVC has a compiler intrinsic for this, it'll be here:

http://msdn.microsoft.com/en-us/library/26td21ds(VS.85).aspx

Otherwise, you'll have to write it using __asm