fegetround, fesetround

#include <fenv.h>
#include <math.h>
#include <stdio.h>
// #pragma STDC FENV_ACCESS ON
void show_fe_current_rounding_direction(void)
{
    printf("current rounding direction:  ");
    switch (fegetround())
    {
           case FE_TONEAREST:  printf ("FE_TONEAREST");  break;
           case FE_DOWNWARD:   printf ("FE_DOWNWARD");   break;
           case FE_UPWARD:     printf ("FE_UPWARD");     break;
           case FE_TOWARDZERO: printf ("FE_TOWARDZERO"); break;
           default:            printf ("unknown");
    };
    printf("\n");
}
int main(void)
{
    /* デフォルトの丸め方向 */
    show_fe_current_rounding_direction();
    printf("+11.5 -> %+4.1f\n", rint(+11.5)); /* 2つの整数の中間値 */
    printf("+12.5 -> %+4.1f\n", rint(+12.5)); /* 2つの整数の中間値 */
    /* 現在の丸め方向を保存 */
    int curr_direction = fegetround();
    /* 一時的に丸め方向を変更 */
    fesetround(FE_DOWNWARD);
    show_fe_current_rounding_direction();
    printf("+11.5 -> %+4.1f\n", rint(+11.5));
    printf("+12.5 -> %+4.1f\n", rint(+12.5));
    /* デフォルトの丸め方向を復元 */
    fesetround(curr_direction);
    show_fe_current_rounding_direction();
    return 0;
}