finish

static VALUE
ossl_digest_finish(int argc, VALUE *argv, VALUE self)
{
    EVP_MD_CTX *ctx;
    VALUE str;

    rb_scan_args(argc, argv, "01", &str);

    GetDigest(self, ctx);

    if (NIL_P(str)) {
        str = rb_str_new(NULL, EVP_MD_CTX_size(ctx));
    } else {
        StringValue(str);
        rb_str_resize(str, EVP_MD_CTX_size(ctx));
    }

    EVP_DigestFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), NULL);

    return str;
}