Using _BitScanReverse64

How to use

_BitScanReverse64(unsigne开发者_如何学Pythond long * Index,  unsigned __int64 Mask)

in order to find a first position set to 1 in integer?

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Try this:

   unsigned __int64 mask = some_value;
   unsigned long index;
   unsigned char isNonzero = _BitScanReverse64(&index, mask);
   if (!isNonzero) {
      // index variable contains index of the first bit set to 1
   }