array.c:423
static VALUE
rb_ary_unshift_m(argc, argv, ary)
    int argc;
    VALUE *argv;
    VALUE ary;
{
    long len = RARRAY(ary)->len;

    if (argc < 0) {
	rb_raise(rb_eArgError, "negative number of arguments");
    }
    if (argc == 0) return ary;

    /* make rooms by setting the last item */
    rb_ary_store(ary, len + argc - 1, Qnil);

    /* sliding items */
    MEMMOVE(RARRAY(ary)->ptr + argc, RARRAY(ary)->ptr, VALUE, len);
    MEMCPY(RARRAY(ary)->ptr, argv, VALUE, argc);
    
    return ary;
}
