Import of the watch repository from Pebble

src/fw/kernel/util/segment.c

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * 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 "segment.h"
+
+#include "system/passert.h"
+
+#include <stdalign.h>
+
+// Remove once the Bamboo build agents build unit tests with a more
+// C11-compliant compiler (i.e. clang >= 3.5)
+#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) && !defined(_GCC_MAX_ALIGN_T)
+typedef long double max_align_t;
+#endif
+
+static void prv_assert_sane_segment(MemorySegment *segment) {
+  PBL_ASSERT(segment->start <= segment->end,
+             "Segment end points before segment start");
+}
+
+static void * prv_align(void *ptr) {
+  uintptr_t c = (uintptr_t)ptr;
+  // Advance the pointer to the next alignment boundary.
+  return (void *)((c + alignof(max_align_t) - 1) & ~(alignof(max_align_t) - 1));
+}
+
+
+size_t memory_segment_get_size(MemorySegment *segment) {
+  prv_assert_sane_segment(segment);
+  return (size_t)((uintptr_t)segment->end - (uintptr_t)segment->start);
+}
+
+void memory_segment_align(MemorySegment *segment) {
+  segment->start = prv_align(segment->start);
+  prv_assert_sane_segment(segment);
+}
+
+void * memory_segment_split(MemorySegment * restrict parent,
+                            MemorySegment * restrict child, size_t size) {
+  prv_assert_sane_segment(parent);
+  char *child_start = prv_align(parent->start);
+  void *child_end = child_start + size;
+  if (child_end > parent->end) {
+    // Requested size is too big to fit in the parent segment.
+    return NULL;
+  }
+  void *adjusted_parent_start = prv_align(child_end);
+  if (adjusted_parent_start > parent->end) {
+    // The child has left no room for the adjusted parent.
+    return NULL;
+  }
+  parent->start = adjusted_parent_start;
+
+  if (child) {
+    *child = (MemorySegment) {
+      .start = child_start,
+      .end = child_end,
+    };
+  }
+  return child_start;
+}