From 9d8b64dec5454a85b9818272f2102b08dcd898d7 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Mon, 2 Feb 2026 16:42:13 +0800
Subject: [PATCH] improvement

---
 lib/system/alloc.nim   | 25 ++++++++++++++-----------
 tests/align/talign.nim |  2 +-
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/lib/system/alloc.nim b/lib/system/alloc.nim
index ee1b278698..66b63de4a2 100644
--- a/lib/system/alloc.nim
+++ b/lib/system/alloc.nim
@@ -134,7 +134,7 @@ type
 
   BigChunk = object of BaseChunk # not necessarily > PageSize!
     next, prev: PBigChunk    # chunks of the same (or bigger) size
-    alignOffset: int16       # offset from data start to actual Cell (for aligned allocs)
+    alignOffset: uint16       # offset from data start to actual Cell (for aligned allocs)
     data {.align: MemAlign.}: UncheckedArray[byte]      # start of usable memory
 
   HeapLinks = object
@@ -846,6 +846,17 @@ when defined(heaptrack):
   proc heaptrack_malloc(a: pointer, size: int) {.cdecl, importc, dynlib: heaptrackLib.}
   proc heaptrack_free(a: pointer) {.cdecl, importc, dynlib: heaptrackLib.}
 
+proc applyAlignment(basePtr: pointer, alignment: int, offset: int, c: PBigChunk): pointer {.inline.} =
+  # Apply alignment if needed: align (basePtr + offset) to alignment boundary
+  if alignment > MemAlign:
+    let base = basePtr +! offset
+    let alignOffset = alignment - (cast[int](base) and (alignment - 1))
+    result = base +! alignOffset
+    c.alignOffset = cast[uint16](alignOffset + offset)
+  else:
+    c.alignOffset = 0
+    result = basePtr
+
 proc rawAlloc(a: var MemRegion, requestedSize: int, alignment: int = MemAlign, offset: int = 0): pointer =
   when defined(nimTypeNames):
     inc(a.allocCounter)
@@ -963,16 +974,8 @@ proc rawAlloc(a: var MemRegion, requestedSize: int, alignment: int = MemAlign, o
     sysAssert c.prev == nil, "rawAlloc 10"
     sysAssert c.next == nil, "rawAlloc 11"
     result = addr(c.data)
-    
     # Apply alignment if needed: align (result + offset) to alignment boundary
-    if alignment > MemAlign:
-      let mask = alignment - 1
-      let alignedUserData = (cast[int](result) + offset + mask) and not mask
-      let finalResult = cast[pointer](alignedUserData - offset)
-      c.alignOffset = cast[int16](cast[int](finalResult) - cast[int](result))
-      result = finalResult
-    else:
-      c.alignOffset = 0
+    result = applyAlignment(result, alignment, offset, c)
 
     sysAssert((cast[int](c) and (MemAlign-1)) == 0, "rawAlloc 13")
     sysAssert((cast[int](c) and PageMask) == 0, "rawAlloc: Not aligned on a page boundary")
@@ -1085,7 +1088,7 @@ when not defined(gcDestructors):
         else:
           var c = cast[PBigChunk](c)
           # Use stored alignOffset to find the actual Cell location
-          let cellPtr = cast[pointer](cast[int](addr(c.data)) + c.alignOffset)
+          let cellPtr = cast[pointer](cast[int](addr(c.data)) + cast[int](c.alignOffset))
           result = p == cellPtr and cast[ptr FreeCell](p).zeroField >% 1
 
   proc prepareForInteriorPointerChecking(a: var MemRegion) {.inline.} =
diff --git a/tests/align/talign.nim b/tests/align/talign.nim
index 46b8f64a29..9ac7c8d544 100644
--- a/tests/align/talign.nim
+++ b/tests/align/talign.nim
@@ -1,6 +1,6 @@
 discard """
 ccodeCheck: "\\i @'NIM_ALIGN(128) NI mylocal1' .*"
-matrix: "--mm:refc -d:useGcAssert; --mm:orc"
+matrix: "--mm:refc -d:useGcAssert -d:useSysAssert; --mm:orc"
 targets: "c cpp"
 output: "align ok"
 """