Vector macros in C

#define ASSERT(a, msg) do { if(!(a)) fprintf(stderr, "%s:%s:%d - %s\n", __FILE__, __FUNCTION__, __LINE__, (msg)); } while(0)

typedef struct vector2i {
    int32_t x, y;
} Vec2i;

typedef struct small_vector2i {
    int16_t x, y;
} sVec2i;

typedef struct vector2f {
    float x, y;
} Vec2f;

#define vec_neg(a) ({ \
    __auto_type _a = (a); \
    (typeof(_a)) { -_a.x, -_a.y }; \
})

#define vec_add(a, b) ({ \
    __auto_type _a = (a); \
    __auto_type _b = (b); \
    (typeof(_a)) { _a.x + _b.x, _a.y + _b.y }; \
})

#define vec_sub(a, b) ({ \
    __auto_type _a = (a); \
    __auto_type _b = (b); \
    (typeof(_a)) { _a.x - _b.x, _a.y - _b.y }; \
})

#define vec_dot(a, b) ({ \
    __auto_type _a = (a); \
    __auto_type _b = (b); \
    _Generic(_a, \
        sVec2i: (int32_t) _a.x * (int32_t) _b.x + (int32_t) _a.y * (int32_t) _b.y, \
        Vec2i: (int64_t) _a.x * (int64_t) _b.x + (int64_t) _a.y * (int64_t) _b.y, \
        default: _a.x * _b.x + _a.y * _b.y); \
})

#define vec_scale(a, f) ({ \
    __auto_type _a = (a); \
    float _f = (f); \
    (typeof(_a)) { (typeof(_a.x)) ((float) _a.x * _f), (typeof(_a.y)) ((float) _a.y * _f) }; \
})

#define vec_normalize(a) ({ \
    __auto_type _a = (a); \
    ASSERT(_Generic(_a, \
        Vec2f: 1, \
        default: 0), "bad type for normalize"); \
    const float invSqrt = 1.0f / sqrtf(_a.x * _a.x + _a.y * _a.y); \
    (Vec2f) { _a.x * invSqrt, _a.y * invSqrt }; \
})

#define vec_dist_sq(a, b) ({ \
    __auto_type _a = (a); \
    __auto_type _b = (b); \
    typeof(_a) _delta = { _a.x - _b.x, _a.y - _b.y }; \
    _Generic(_delta, \
        sVec2i: (int32_t) _delta.x * (int32_t) _delta.x + (int32_t) _delta.y * (int32_t) _delta.y, \
        Vec2i: (int64_t) _delta.x * (int64_t) _delta.x + (int64_t) _delta.y * (int64_t) _delta.y, \
        default: _delta.x * _delta.x + _delta.y * _delta.y); \
})