memory alignment of binary128

binary128.c

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

#include <endian.h>

typedef union
{
    __float128  val;
    struct
    {
#if __BYTE_ORDER == __BIG_ENDIAN
        uint64_t sign    : 1;
        uint64_t exp     : 15;
        uint64_t frac1   : 48;
        uint64_t frac0   : 64;
#else
        uint64_t frac0   : 64;
        uint64_t frac1   : 48;
        uint64_t exp     : 15;
        uint64_t sign    : 1;
#endif
    } bits;
} qfloat;

int main()
{
    qfloat      foo;
    qfloat      bar;

    foo.val = 65536.0;

    foo.val += 1.0;
    foo.val *= foo.val;

    bar.val = 8191.0;

    printf("%04X %012llX %016llX\n", (uint16_t)foo.bits.exp, (uint64_t)foo.bits.frac1, foo.bits.frac0);

    return 0;
}