OpenSSL::Digest#finish

static VALUE
ossl_digest_finish(VALUE self)
{
    EVP_MD_CTX *ctx;
    VALUE str;

    GetDigest(self, ctx);
    str = rb_str_new(NULL, EVP_MD_CTX_size(ctx));
    if (!EVP_DigestFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), NULL))
        ossl_raise(eDigestError, "EVP_DigestFinal_ex");

    return str;
}