acos

/*
 *  call-seq:
 *     Math.acos(x)    => float
 *  
 *  Computes the arc cosine of <i>x</i>. Returns 0..PI.
 */

static VALUE
math_acos(obj, x)
    VALUE obj, x;
{
    double d;

    Need_Float(x);
    errno = 0;
    d = acos(RFLOAT(x)->value);
    domain_check(d, "acos");
    return rb_float_new(d);
}