To duplicate a CPU set, use memcpy(3).
   Since CPU sets are bit masks allocated in units of long words, the
   actual number of CPUs in a dynamically allocated CPU set will be
   rounded up to the next multiple of sizeof(unsigned long).  An
   application should consider the contents of these extra bits to be
   undefined.

#ifndef HAVE_CPUID_T
#ifdef __linux__
typedef int cpuid_t;
#endif
#ifdef __FreeBSD__
typedef size_t cpuid_t;
#endif
#endif

$ grep -IR cpu_set_t /usr/include
/usr/include/x86_64-linux-gnu/bits/cpu-set.h:} cpu_set_t;
...

typedef struct
{
  __cpu_mask __bits[__CPU_SETSIZE / __NCPUBITS];
} cpu_set_t;

/usr/include/x86_64-linux-gnu/bits/cpu-set.h:typedef __CPU_MASK_TYPE __cpu_mask;

$ grep -IR __CPU_MASK_TYPE /usr/include
/usr/include/x86_64-linux-gnu/bits/typesizes.h:#define __CPU_MASK_TYPE 	__SYSCALL_ULONG_TYPE

$ grep -IR __SYSCALL_ULONG_TYPE /usr/include
/usr/include/x86_64-linux-gnu/bits/typesizes.h:# define __SYSCALL_ULONG_TYPE	__UQUAD_TYPE
/usr/include/x86_64-linux-gnu/bits/typesizes.h:# define __SYSCALL_ULONG_TYPE	__ULONGWORD_TYPE

/usr/include/x86_64-linux-gnu/bits/typesizes.h:# define __SYSCALL_ULONG_TYPE	__ULONGWORD_TYPE
...
/usr/include/x86_64-linux-gnu/bits/typesizes.h:# define __SYSCALL_ULONG_TYPE	__ULONGWORD_TYPE
/usr/include/x86_64-linux-gnu/bits/types.h:#define __ULONGWORD_TYPE	unsigned long int

$ grep -IR __UQUAD_TYPE /usr/include
...
/usr/include/x86_64-linux-gnu/bits/types.h:# define __UQUAD_TYPE		__u_quad_t
/usr/include/x86_64-linux-gnu/bits/types.h:# define __UQUAD_TYPE		unsigned long int

./nsd.c:			cpuset_set((cpuid_t)opt->cpu, nsd.cpuset);
./nsd.c:			cpuset_set((cpuid_t)cpu, nsd.xfrd_cpuset);

$ cat t.c
#include <stdio.h>
int main(void)
{
  printf("sizeof unsigned long int: %d\n", (int)(sizeof(unsigned long int)));
}

$ ./t
sizeof unsigned long int: 8

/* quad_t is also 64 bits.  */
#if __WORDSIZE == 64
typedef long int __quad_t;
typedef unsigned long int __u_quad_t;
#elif defined __GLIBC_HAVE_LONG_LONG
__extension__ typedef long long int __quad_t;
__extension__ typedef unsigned long long int __u_quad_t;
#else
typedef struct
{
  long __val[2];
} __quad_t;
typedef struct
{
  __u_long __val[2];
} __u_quad_t;
#endif