OpenSSL::HMAC#initialize_copy

static VALUE
ossl_hmac_copy(VALUE self, VALUE other)
{
    EVP_MD_CTX *ctx1, *ctx2;

    rb_check_frozen(self);
    if (self == other) return self;

    GetHMAC(self, ctx1);
    GetHMAC(other, ctx2);
    if (EVP_MD_CTX_copy(ctx1, ctx2) != 1)
        ossl_raise(eHMACError, "EVP_MD_CTX_copy");
    return self;
}