From 2899588f28f4d02a61a19ecc8454ddaf14c7b6b3 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Mon, 15 Jun 2020 00:56:09 +0200
Subject: [PATCH] src: simplify alignment-handling code
MIME-Version: 1.0
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Use a common function to handle alignment computations in
multiple places.

PR-URL: https://github.com/nodejs/node/pull/33884
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
---
 src/node_http2.cc          | 4 +---
 src/node_http_common-inl.h | 3 +--
 src/string_bytes.cc        | 6 ++----
 src/util-inl.h             | 9 +++------
 src/util.h                 | 7 +++++++
 5 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/src/node_http2.cc b/src/node_http2.cc
index 4d1309e08a1a78..de7a7f044e28c2 100644
--- a/src/node_http2.cc
+++ b/src/node_http2.cc
@@ -373,9 +373,7 @@ Origins::Origins(
                               origin_string_len);
 
   // Make sure the start address is aligned appropriately for an nghttp2_nv*.
-  char* start = reinterpret_cast<char*>(
-      RoundUp(reinterpret_cast<uintptr_t>(buf_.data()),
-              alignof(nghttp2_origin_entry)));
+  char* start = AlignUp(buf_.data(), alignof(nghttp2_origin_entry));
   char* origin_contents = start + (count_ * sizeof(nghttp2_origin_entry));
   nghttp2_origin_entry* const nva =
       reinterpret_cast<nghttp2_origin_entry*>(start);
diff --git a/src/node_http_common-inl.h b/src/node_http_common-inl.h
index 54f2faf39c49bc..7cd4bdec99c3d6 100644
--- a/src/node_http_common-inl.h
+++ b/src/node_http_common-inl.h
@@ -31,8 +31,7 @@ NgHeaders<T>::NgHeaders(Environment* env, v8::Local<v8::Array> headers) {
                                  count_ * sizeof(nv_t) +
                                  header_string_len);
 
-  char* start = reinterpret_cast<char*>(
-      RoundUp(reinterpret_cast<uintptr_t>(*buf_), alignof(nv_t)));
+  char* start = AlignUp(buf_.out(), alignof(nv_t));
   char* header_contents = start + (count_ * sizeof(nv_t));
   nv_t* const nva = reinterpret_cast<nv_t*>(start);
 
diff --git a/src/string_bytes.cc b/src/string_bytes.cc
index e0c2d6901fc429..68c7c06d8df1de 100644
--- a/src/string_bytes.cc
+++ b/src/string_bytes.cc
@@ -273,16 +273,14 @@ size_t StringBytes::WriteUCS2(Isolate* isolate,
     return 0;
   }
 
+  uint16_t* const aligned_dst = AlignUp(dst, sizeof(*dst));
   size_t nchars;
-  size_t alignment = reinterpret_cast<uintptr_t>(dst) % sizeof(*dst);
-  if (alignment == 0) {
+  if (aligned_dst == dst) {
     nchars = str->Write(isolate, dst, 0, max_chars, flags);
     *chars_written = nchars;
     return nchars * sizeof(*dst);
   }
 
-  uint16_t* aligned_dst =
-      reinterpret_cast<uint16_t*>(buf + sizeof(*dst) - alignment);
   CHECK_EQ(reinterpret_cast<uintptr_t>(aligned_dst) % sizeof(*dst), 0);
 
   // Write all but the last char
diff --git a/src/util-inl.h b/src/util-inl.h
index 6b4bdfe034d64f..1af87d492ade06 100644
--- a/src/util-inl.h
+++ b/src/util-inl.h
@@ -208,8 +208,7 @@ void SwapBytes16(char* data, size_t nbytes) {
   CHECK_EQ(nbytes % 2, 0);
 
 #if defined(_MSC_VER)
-  int align = reinterpret_cast<uintptr_t>(data) % sizeof(uint16_t);
-  if (align == 0) {
+  if (AlignUp(data, sizeof(uint16_t)) == data) {
     // MSVC has no strict aliasing, and is able to highly optimize this case.
     uint16_t* data16 = reinterpret_cast<uint16_t*>(data);
     size_t len16 = nbytes / sizeof(*data16);
@@ -232,9 +231,8 @@ void SwapBytes32(char* data, size_t nbytes) {
   CHECK_EQ(nbytes % 4, 0);
 
 #if defined(_MSC_VER)
-  int align = reinterpret_cast<uintptr_t>(data) % sizeof(uint32_t);
   // MSVC has no strict aliasing, and is able to highly optimize this case.
-  if (align == 0) {
+  if (AlignUp(data, sizeof(uint32_t)) == data) {
     uint32_t* data32 = reinterpret_cast<uint32_t*>(data);
     size_t len32 = nbytes / sizeof(*data32);
     for (size_t i = 0; i < len32; i++) {
@@ -256,8 +254,7 @@ void SwapBytes64(char* data, size_t nbytes) {
   CHECK_EQ(nbytes % 8, 0);
 
 #if defined(_MSC_VER)
-  int align = reinterpret_cast<uintptr_t>(data) % sizeof(uint64_t);
-  if (align == 0) {
+  if (AlignUp(data, sizeof(uint64_t)) == data) {
     // MSVC has no strict aliasing, and is able to highly optimize this case.
     uint64_t* data64 = reinterpret_cast<uint64_t*>(data);
     size_t len64 = nbytes / sizeof(*data64);
diff --git a/src/util.h b/src/util.h
index 8cec9a8aab956b..2a4d6e27d59d9e 100644
--- a/src/util.h
+++ b/src/util.h
@@ -729,6 +729,13 @@ constexpr T RoundUp(T a, T b) {
   return a % b != 0 ? a + b - (a % b) : a;
 }
 
+// Align ptr to an `alignment`-bytes boundary.
+template <typename T, typename U>
+constexpr T* AlignUp(T* ptr, U alignment) {
+  return reinterpret_cast<T*>(
+      RoundUp(reinterpret_cast<uintptr_t>(ptr), alignment));
+}
+
 class SlicedArguments : public MaybeStackBuffer<v8::Local<v8::Value>> {
  public:
   inline explicit SlicedArguments(