Portable code for https://outerproduct.net/trivial/2023-01-11_nan.html GCC compiles this right

f32.c

#include <math.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

/* quiet NANs aren't always defined???
   confused about this bit
 */
#define F32 NAN

struct f32;

static struct f32 f32_unbox(uint64_t x);
static uint64_t f32_box(struct f32 x);
static struct f32 f32_add(struct f32 x, struct f32 y);

struct f32 {
        float tag;
        float value;
};

int main(int argc, char **argv)
{
        float tag = F32;
        float value = 8;
        printf("%f %f\n", tag, value);
        return 0;
}

uint64_t add_raw(uint64_t x, uint64_t y)
{
        return f32_box(f32_add(f32_unbox(x), f32_unbox(y)));
}

static uint64_t f32_box(struct f32 x)
{
        uint64_t y = {0};
        memcpy(&y, &x, sizeof y);
        return y;
}

static struct f32 f32_unbox(uint64_t x)
{
        struct f32 y = {0};
        memcpy(&y, &x, sizeof y);
        return y;
}

static struct f32 f32_add(struct f32 x, struct f32 y)
{
        return (struct f32) {
                .value = x.value + y.value,
                .tag = x.tag + y.tag
        };
}