feat: add example curve for testing (PROOF-642) (#32)

* add example element

* comment

sxt/base/curve/example_element.cc

@@ -0,0 +1,17 @@
+/** Proofs GPU - Space and Time's cryptographic proof algorithms on the CPU and GPU.
+ *
+ * Copyright 2023-present Space and Time Labs, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "sxt/base/curve/example_element.h"

sxt/base/curve/example_element.h

@@ -0,0 +1,102 @@
+/** Proofs GPU - Space and Time's cryptographic proof algorithms on the CPU and GPU.
+ *
+ * Copyright 2023-present Space and Time Labs, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <cstdint>
+#include <iostream>
+
+#include "sxt/base/macro/cuda_callable.h"
+
+namespace sxt::bascrv {
+//--------------------------------------------------------------------------------------------------
+// element97
+//--------------------------------------------------------------------------------------------------
+/**
+ * Integer arithmetic mod 97.
+ *
+ * Provides a minimal implementation of the curve element concent that can be used for writing
+ * tests.
+ */
+struct element97 {
+  uint32_t value;
+  bool marked = false;
+
+  element97() noexcept = default;
+
+  constexpr element97(uint32_t val) noexcept : value{val % 97u} {}
+
+  static constexpr element97 identity() noexcept { return {0}; }
+
+  bool operator==(const element97&) const noexcept = default;
+};
+
+//--------------------------------------------------------------------------------------------------
+// operator<<
+//--------------------------------------------------------------------------------------------------
+inline std::ostream& operator<<(std::ostream& out, const element97& e) noexcept {
+  out << e.value;
+  return out;
+}
+
+//--------------------------------------------------------------------------------------------------
+// double_element
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void double_element(element97& res, const element97& e) noexcept {
+  res.value = (e.value + e.value) % 97u;
+}
+
+//--------------------------------------------------------------------------------------------------
+// neg
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void neg(element97& res, const element97& e) noexcept {
+  res.value = (97u - e.value) % 97u;
+}
+
+//--------------------------------------------------------------------------------------------------
+// cneg
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void cneg(element97& res, int b) noexcept {
+  if (b) {
+    res.value = (97u - res.value) % 97u;
+  }
+}
+
+//--------------------------------------------------------------------------------------------------
+// add
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void add(element97& res, const element97& x, const element97& y) noexcept {
+  res.value = (x.value + y.value) % 97u;
+}
+
+//--------------------------------------------------------------------------------------------------
+// add_inplace
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void add_inplace(element97& res, element97& x) noexcept {
+  res.value = (res.value + x.value) % 97u;
+  x = 13; // simulate a destructive add by setting x to an arbitrary value
+}
+
+//--------------------------------------------------------------------------------------------------
+// mark
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE void mark(element97& res) noexcept { res.marked = true; }
+
+//--------------------------------------------------------------------------------------------------
+// is_marked
+//--------------------------------------------------------------------------------------------------
+inline CUDA_CALLABLE bool is_marked(const element97& e) noexcept { return e.marked; }
+} // namespace sxt::bascrv

sxt/base/curve/example_element.t.cc

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+/** Proofs GPU - Space and Time's cryptographic proof algorithms on the CPU and GPU.
+ *
+ * Copyright 2023-present Space and Time Labs, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "sxt/base/curve/example_element.h"
+
+#include "sxt/base/curve/element.h"
+#include "sxt/base/test/unit_test.h"
+
+using namespace sxt;
+using namespace sxt::bascrv;
+
+TEST_CASE("element97 satifies the curve concept") { REQUIRE(bascrv::element<element97>); }