Start work on buffer

asl/BUILD.bazel

@@ -5,6 +5,7 @@ cc_library(
         "annotations.hpp",
         "assert.hpp",
         "box.hpp",
+        "buffer.hpp",
         "config.hpp",
         "float.hpp",
         "format.hpp",
@@ -45,6 +46,7 @@ cc_library(
     ],
 ) for name in [
     "box",
+    "buffer",
     "float",
     "format",
     "functional",

asl/box.hpp

@@ -5,7 +5,6 @@
 #include "asl/annotations.hpp"
 #include "asl/memory.hpp"
 #include "asl/utility.hpp"
-#include "asl/box.hpp"
 
 namespace asl
 {

asl/buffer.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+#include "asl/meta.hpp"
+#include "asl/allocator.hpp"
+#include "asl/annotations.hpp"
+
+namespace asl
+{
+
+template<is_object T, allocator Allocator = DefaultAllocator>
+class buffer
+{
+    
+    T*         m_data{};
+    isize_t    m_capacity{};
+
+    // bit 63       : 0 = on heap, 1 = inline
+    // bits [62:56] : size when inline
+    // bits [52:0]  : size when on heap
+    size_t     m_size_encoded{};
+
+    ASL_NO_UNIQUE_ADDRESS Allocator m_allocator;
+    
+    static_assert(align_of<T> <= align_of<T*>);
+    static_assert(align_of<T*> == align_of<isize_t>);
+    static_assert(align_of<T*> == align_of<size_t>);
+    
+public:
+
+    static constexpr isize_t kInlineCapacity = []() {
+        // 1 byte is used for size inline in m_size_encoded.
+        // This is enough because we have at most 24 bytes available,
+        // so 23 chars of capacity.
+        const isize_t available_size = size_of<T*> + size_of<isize_t> + size_of<size_t> - 1;
+        return available_size / size_of<T>;
+    }();
+
+    constexpr buffer() requires default_constructible<Allocator> = default;
+
+    explicit constexpr buffer(Allocator allocator)
+        : m_allocator{ASL_MOVE(allocator)}
+    {}
+};
+
+} // namespace asl
+

asl/layout.hpp

@@ -33,3 +33,5 @@ struct layout
 };
 
 } // namespace asl
+
+#define AslOffsetOf(S, M) (static_cast<isize_t>(__builtin_offsetof(S, M)))

asl/tests/buffer_tests.cpp

@@ -0,0 +1,8 @@
+#include <asl/buffer.hpp>
+
+#include <asl/testing/testing.hpp>
+
+static_assert(asl::buffer<int32_t>::kInlineCapacity == 5);
+static_assert(asl::buffer<int64_t>::kInlineCapacity == 2);
+static_assert(asl::buffer<char>::kInlineCapacity == 23);
+