Generic popcnt

popcnt.c

#include <limits.h>
#include <stddef.h>
#include <stdint.h>

#define popcnt(x) (size_t)({\
        typeof (_Generic(x,  \
      int32_t: (uint32_t)1,   \
      int64_t: (uint64_t)1,    \
     uint32_t: (uint32_t)1,     \
     uint64_t: (uint64_t)1))y=x; \
     y-=y>>1U& (typeof(y))-1/ 3; \
     y=(y>>2U& (typeof(y))-1/ 5) \
     + (y    & (typeof(y))-1/ 5);\
    (y+(y>>4)& (typeof(y))-1/17) \
     * (       (typeof(y))-1/255)\
    >>CHAR_BIT*(sizeof(y) -1);  })
size_t popcnt32(uint32_t x){return popcnt(x);}
size_t popcnt64(uint64_t x){return popcnt(x);}