test.c

#pragma STDC FENV_ACCESS ON
#include <signal.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>

static void check(const char *where) {
    printf("%-40s: fegetround() => %#x\n", where, fegetround());
}

static void handler(int _) {
    check("in signal handler before fesetround");
    assert(!fesetround(FE_DOWNWARD));
    check("in signal handler after fesetround");
}

int main() {
    int round = FE_UPWARD;
    printf("fesetround(%#x)\n", round);
    assert(!fesetround(round));
    check("before signal handler");
    assert(SIG_ERR != signal(SIGINT, handler));
    assert(!raise(SIGINT));

    check("after signal handler");
}