From f733b9cc15452116b40500eb89b00f5c63fd9dfd Mon Sep 17 00:00:00 2001
From: Chuck Walbourn <walbourn@users.noreply.github.com>
Date: Thu, 15 Feb 2018 18:05:02 -0800
Subject: [PATCH] AlignUp, AlignDown helpers (#29)

---
 Inc/DirectXHelpers.h    | 25 +++++++++++++++++++++++++
 Src/LinearAllocator.cpp | 18 ++----------------
 2 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/Inc/DirectXHelpers.h b/Inc/DirectXHelpers.h
index 4080b056..57447ac4 100644
--- a/Inc/DirectXHelpers.h
+++ b/Inc/DirectXHelpers.h
@@ -173,4 +173,29 @@ namespace DirectX
 
         commandList->ResourceBarrier(1, &desc);
     }
+
+    // Helpers for aligning values by a power of 2
+    template<typename T>
+    inline T AlignDown(T size, size_t alignment)
+    {
+        if (alignment > 0)
+        {
+            assert(((alignment - 1) & alignment) == 0);
+            T mask = static_cast<T>(alignment - 1);
+            return size & ~mask;
+        }
+        return size;
+    }
+
+    template<typename T>
+    inline T AlignUp(T size, size_t alignment)
+    {
+        if (alignment > 0)
+        {
+            assert(((alignment - 1) & alignment) == 0);
+            T mask = static_cast<T>(alignment - 1);
+            return (size + mask) & ~mask;
+        }
+        return size;
+    }
 }
\ No newline at end of file
diff --git a/Src/LinearAllocator.cpp b/Src/LinearAllocator.cpp
index 49be2c0e..660db71e 100644
--- a/Src/LinearAllocator.cpp
+++ b/Src/LinearAllocator.cpp
@@ -25,20 +25,6 @@
 using namespace DirectX;
 using Microsoft::WRL::ComPtr;
 
-namespace
-{
-    inline size_t AlignOffset(size_t offset, size_t alignment)
-    {
-        if (alignment > 0)
-        {
-            // Alignment must be a power of 2
-            assert((alignment & (alignment - 1)) == 0);
-            offset = (offset + alignment - 1) & ~(alignment - 1);
-        }
-        return offset;
-    }
-}
-
 LinearAllocatorPage::LinearAllocatorPage()
     : pPrevPage(nullptr)
     , pNextPage(nullptr)
@@ -53,7 +39,7 @@ LinearAllocatorPage::LinearAllocatorPage()
 
 size_t LinearAllocatorPage::Suballocate(_In_ size_t size, _In_ size_t alignment)
 {
-    size_t offset = AlignOffset(mOffset, alignment);
+    size_t offset = AlignUp(mOffset, alignment);
 #ifdef _DEBUG
     if (offset + size > mSize)
         throw std::exception("Out of free memory in page suballoc");
@@ -278,7 +264,7 @@ LinearAllocatorPage* LinearAllocator::FindPageForAlloc(
 {
     for (LinearAllocatorPage* page = list; page != nullptr; page = page->pNextPage)
     {
-        size_t offset = AlignOffset(page->mOffset, alignment);
+        size_t offset = AlignUp(page->mOffset, alignment);
         if (offset + sizeBytes <= m_increment)
             return page;
     }