/* gcc acos.c
 * expected output: acos(2) = 0.0000 -1.3170i
 * output on musl:  acos(2) = 2.8878 -1.5708i
 */
#include <stdio.h>
#include <complex.h>

int main() {
  double complex arg = 2;
  double complex res = cacos(arg);
  printf("acos(2) = %.4lf %+.4lfi\n", creal(res), cimag(res));
}