first

static VALUE
arith_seq_first(int argc, VALUE *argv, VALUE self)
{
    VALUE b, e, s, ary;
    long n;
    int x;

    rb_check_arity(argc, 0, 1);

    b = arith_seq_begin(self);
    e = arith_seq_end(self);
    s = arith_seq_step(self);
    if (argc == 0) {
        if (!NIL_P(e)) {
            VALUE zero = INT2FIX(0);
            int r = rb_cmpint(rb_num_coerce_cmp(s, zero, idCmp), s, zero);
            if (r > 0 && RTEST(rb_funcall(b, '>', 1, e))) {
                return Qnil;
            }
            if (r < 0 && RTEST(rb_funcall(b, '<', 1, e))) {
                return Qnil;
            }
        }
        return b;
    }

    /* TODO: the following code should be extracted as arith_seq_take */

    n = NUM2LONG(argv[0]);
    if (n < 0) {
        rb_raise(rb_eArgError, "attempt to take negative size");
    }
    if (n == 0) {
        return rb_ary_new_capa(0);
    }

    x = arith_seq_exclude_end_p(self);

    if (FIXNUM_P(b) && NIL_P(e) && FIXNUM_P(s)) {
        long i = FIX2LONG(b), unit = FIX2LONG(s);
        ary = rb_ary_new_capa(n);
        while (n > 0 && FIXABLE(i)) {
            rb_ary_push(ary, LONG2FIX(i));
            i += unit;  /* FIXABLE + FIXABLE never overflow; */
            --n;
        }
        if (n > 0) {
            b = LONG2NUM(i);
            while (n > 0) {
                rb_ary_push(ary, b);
                b = rb_big_plus(b, s);
                --n;
            }
        }
        return ary;
    }
    else if (FIXNUM_P(b) && FIXNUM_P(e) && FIXNUM_P(s)) {
        long i = FIX2LONG(b);
        long end = FIX2LONG(e);
        long unit = FIX2LONG(s);
        long len;

        if (unit >= 0) {
            if (!x) end += 1;

            len = end - i;
            if (len < 0) len = 0;
            ary = rb_ary_new_capa((n < len) ? n : len);
            while (n > 0 && i < end) {
                rb_ary_push(ary, LONG2FIX(i));
                if (i + unit < i) break;
                i += unit;
                --n;
            }
        }
        else {
            if (!x) end -= 1;

            len = i - end;
            if (len < 0) len = 0;
            ary = rb_ary_new_capa((n < len) ? n : len);
            while (n > 0 && i > end) {
                rb_ary_push(ary, LONG2FIX(i));
                if (i + unit > i) break;
                i += unit;
                --n;
            }
        }
        return ary;
    }
    else if (RB_FLOAT_TYPE_P(b) || RB_FLOAT_TYPE_P(e) || RB_FLOAT_TYPE_P(s)) {
        /* generate values like ruby_float_step */

        double unit = NUM2DBL(s);
        double beg = NUM2DBL(b);
        double end = NIL_P(e) ? (unit < 0 ? -1 : 1)*HUGE_VAL : NUM2DBL(e);
        double len = ruby_float_step_size(beg, end, unit, x);
        long i;

        if (n > len)
            n = (long)len;

        if (isinf(unit)) {
            if (len > 0) {
                ary = rb_ary_new_capa(1);
                rb_ary_push(ary, DBL2NUM(beg));
            }
            else {
                ary = rb_ary_new_capa(0);
            }
        }
        else if (unit == 0) {
            VALUE val = DBL2NUM(beg);
            ary = rb_ary_new_capa(n);
            for (i = 0; i < len; ++i) {
                rb_ary_push(ary, val);
            }
        }
        else {
            ary = rb_ary_new_capa(n);
            for (i = 0; i < n; ++i) {
                double d = i*unit+beg;
                if (unit >= 0 ? end < d : d < end) d = end;
                rb_ary_push(ary, DBL2NUM(d));
            }
        }

        return ary;
    }

    return rb_call_super(argc, argv);
}