chore: checkpoint before Python removal

vendor/aws-lc-sys/aws-lc/crypto/refcount_c11.c

@@ -0,0 +1,56 @@
+// Copyright (c) 2015, Google Inc.
+// SPDX-License-Identifier: ISC
+
+#include "internal.h"
+
+
+#if defined(OPENSSL_C11_ATOMIC)
+
+#include <assert.h>
+#include <stdalign.h>
+#include <stdatomic.h>
+#include <stdlib.h>
+
+#include <openssl/type_check.h>
+
+
+// See comment above the typedef of CRYPTO_refcount_t about these tests.
+OPENSSL_STATIC_ASSERT(alignof(CRYPTO_refcount_t) == alignof(_Atomic CRYPTO_refcount_t),
+              _Atomic_alters_the_needed_alignment_of_a_reference_count)
+OPENSSL_STATIC_ASSERT(sizeof(CRYPTO_refcount_t) == sizeof(_Atomic CRYPTO_refcount_t),
+              _Atomic_alters_the_size_of_a_reference_count)
+
+OPENSSL_STATIC_ASSERT((CRYPTO_refcount_t)-1 == CRYPTO_REFCOUNT_MAX,
+              CRYPTO_REFCOUNT_MAX_is_incorrect)
+
+void CRYPTO_refcount_inc(CRYPTO_refcount_t *in_count) {
+  _Atomic CRYPTO_refcount_t *count = (_Atomic CRYPTO_refcount_t *) in_count;
+  uint32_t expected = atomic_load(count);
+
+  while (expected != CRYPTO_REFCOUNT_MAX) {
+    uint32_t new_value = expected + 1;
+    if (atomic_compare_exchange_weak(count, &expected, new_value)) {
+      break;
+    }
+  }
+}
+
+int CRYPTO_refcount_dec_and_test_zero(CRYPTO_refcount_t *in_count) {
+  _Atomic CRYPTO_refcount_t *count = (_Atomic CRYPTO_refcount_t *)in_count;
+  uint32_t expected = atomic_load(count);
+
+  for (;;) {
+    if (expected == 0) {
+      abort();
+    } else if (expected == CRYPTO_REFCOUNT_MAX) {
+      return 0;
+    } else {
+      const uint32_t new_value = expected - 1;
+      if (atomic_compare_exchange_weak(count, &expected, new_value)) {
+        return new_value == 0;
+      }
+    }
+  }
+}
+
+#endif  // OPENSSL_C11_ATOMIC