收录日期:2020/12/02 10:51:33 时间:2008-09-29 10:49:28 标签:c++,c,64bit,bit-manipulation

Suppose I have one long long int and want to take its bits and construct four unsigned short ints out of it.

Particular order doesn't matter much here.

I generally know that I need to shift bits and truncate to the size of unsigned short int. But I think I may make some weird mistake somewhere, so I ask.

#include <stdint.h>
#include <stdio.h>

union ui64 {
    uint64_t one;
    uint16_t four[4];
};

int
main()
{
    union ui64 number = {0x123456789abcdef0};
    printf("%x %x %x %x\n", number.four[0], number.four[1],
                            number.four[2], number.four[3]);
    return 0;
}
(unsigned short)((((unsigned long long int)value)>>(x))&(0xFFFF))

where value is your long long int, and x is 0, 16, 32 or 48 for the four shorts.

union LongLongIntToThreeUnsignedShorts {
   long long int long_long_int;
   unsigned short int short_ints[sizeof(long long int) / sizeof(short int)];
};

That should do what you are thinking about, without having to mess around with bit shifting.