[libc-commits] [libc] [libc] Use Block as a byte-backed proxy (PR #201001)

[Daniel Thornburgh via libc-commits]

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@@ -90,48 +98,69 @@ using cpp::optional;
 ///
 /// The next offset of a block matches the previous offset of its next block.
 /// The first block in a list is denoted by having a previous offset of `0`.
-class Block {
-  // Masks for the contents of the next_ field.
+class BlockRef {
+  // Masks for the contents of the next field.
   static constexpr size_t PREV_FREE_MASK = 1 << 0;
   static constexpr size_t LAST_MASK = 1 << 1;
   static constexpr size_t SIZE_MASK = ~(PREV_FREE_MASK | LAST_MASK);
 
+  // Header field offsets. The previous offset is only meaningful when this
+  // block's PREV_FREE_MASK bit is set in the next field.
+  static constexpr size_t PREV_OFFSET = 0;
+  static constexpr size_t NEXT_OFFSET = sizeof(size_t);
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mysterymath wrote:

nit: `= PREV_OFFSET + sizeof(size_t)`

This gives the same form to the expression below.

https://github.com/llvm/llvm-project/pull/201001