Update documentation regarding alignment issue.

3 files changed, 95 insertions, 67 deletions

diff --git a/doc/StlContainers.dox b/doc/StlContainers.dox
index e0f8714a9..665a54793 100644
--- a/doc/StlContainers.dox
+++ b/doc/StlContainers.dox
@@ -6,31 +6,39 @@ namespace Eigen {
 
 \section StlContainers_summary Executive summary
 
-Using STL containers on \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", or classes having members of such types, requires taking the following two steps:
+If you're compiling in \cpp17 mode only with a sufficiently recent compiler (e.g., GCC>=7, clang>=5, MSVC>=19.12), then everything is taken care by the compiler and you can stop reading.
 
-\li A 16-byte-aligned allocator must be used. Eigen does provide one ready for use: aligned_allocator.
-\li If you want to use the std::vector container, you need to \#include <Eigen/StdVector>.
+Otherwise, using STL containers on \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", or classes having members of such types, requires the use of an over-aligned allocator.
+That is, an allocator capable of allocating buffers with 16, 32, or even 64 bytes alignment.
+%Eigen does provide one ready for use: aligned_allocator.
 
-These issues arise only with \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types" and \ref TopicStructHavingEigenMembers "structures having such Eigen objects as member". For other Eigen types, such as Vector3f or MatrixXd, no special care is needed when using STL containers.
+Prior to \cpp11, if you want to use the `std::vector` container, then you also have to `#include <Eigen/StdVector>`.
+
+These issues arise only with \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types" and \ref TopicStructHavingEigenMembers "structures having such Eigen objects as member".
+For other %Eigen types, such as Vector3f or MatrixXd, no special care is needed when using STL containers.
 
 \section allocator Using an aligned allocator
 
-STL containers take an optional template parameter, the allocator type. When using STL containers on \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", you need tell the container to use an allocator that will always allocate memory at 16-byte-aligned locations. Fortunately, Eigen does provide such an allocator: Eigen::aligned_allocator.
+STL containers take an optional template parameter, the allocator type. When using STL containers on \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", you need tell the container to use an allocator that will always allocate memory at 16-byte-aligned (or more) locations. Fortunately, %Eigen does provide such an allocator: Eigen::aligned_allocator.
 
 For example, instead of
 \code
-std::map<int, Eigen::Vector4f>
+std::map<int, Eigen::Vector4d>
 \endcode
 you need to use
 \code
-std::map<int, Eigen::Vector4f, std::less<int>, 
-         Eigen::aligned_allocator<std::pair<const int, Eigen::Vector4f> > >
+std::map<int, Eigen::Vector4d, std::less<int>, 
+         Eigen::aligned_allocator<std::pair<const int, Eigen::Vector4d> > >
 \endcode
-Note that the third parameter "std::less<int>" is just the default value, but we have to include it because we want to specify the fourth parameter, which is the allocator type.
+Note that the third parameter `std::less<int>` is just the default value, but we have to include it because we want to specify the fourth parameter, which is the allocator type.
 
 \section StlContainers_vector The case of std::vector
 
-The situation with std::vector was even worse (explanation below) so we had to specialize it for the Eigen::aligned_allocator type. In practice you \b must use the Eigen::aligned_allocator (not another aligned allocator), \b and \#include <Eigen/StdVector>.
+This section is for c++98/03 users only. \cpp11 (or above) users can stop reading here.
+
+So in c++98/03, the situation with `std::vector` is more complicated because of a bug in the standard (explanation below).
+To workaround the issue, we had to specialize it for the Eigen::aligned_allocator type.
+In practice you \b must use the Eigen::aligned_allocator (not another aligned allocator), \b and \#include <Eigen/StdVector>.
 
 Here is an example:
 \code
@@ -39,12 +47,16 @@ Here is an example:
 std::vector<Eigen::Vector4f,Eigen::aligned_allocator<Eigen::Vector4f> >
 \endcode
 
+<span class="note">\b Explanation: The `resize()` method of `std::vector` takes a `value_type` argument (defaulting to `value_type()`). So with `std::vector<Eigen::Vector4d>`, some Eigen::Vector4d objects will be passed by value, which discards any alignment modifiers, so a Eigen::Vector4d can be created at an unaligned location.
+In order to avoid that, the only solution we saw was to specialize `std::vector` to make it work on a slight modification of, here, Eigen::Vector4d, that is able to deal properly with this situation.
+</span>
+
 \subsection vector_spec An alternative - specializing std::vector for Eigen types
 
 As an alternative to the recommended approach described above, you have the option to specialize std::vector for Eigen types requiring alignment. 
-The advantage is that you won't need to declare std::vector all over with Eigen::allocator. One drawback on the other hand side is that
-the specialization needs to be defined before all code pieces in which e.g. std::vector<Vector2d> is used. Otherwise, without knowing the specialization
-the compiler will compile that particular instance with the default std::allocator and you program is most likely to crash.
+The advantage is that you won't need to declare std::vector all over with Eigen::aligned_allocator. One drawback on the other hand side is that
+the specialization needs to be defined before all code pieces in which e.g. `std::vector<Vector2d>` is used. Otherwise, without knowing the specialization
+the compiler will compile that particular instance with the default `std::allocator` and you program is most likely to crash.
 
 Here is an example:
 \code
@@ -54,8 +66,7 @@ EIGEN_DEFINE_STL_VECTOR_SPECIALIZATION(Matrix2d)
 std::vector<Eigen::Vector2d>
 \endcode
 
-<span class="note">\b Explanation: The resize() method of std::vector takes a value_type argument (defaulting to value_type()). So with std::vector<Eigen::Vector4f>, some Eigen::Vector4f objects will be passed by value, which discards any alignment modifiers, so a Eigen::Vector4f can be created at an unaligned location. In order to avoid that, the only solution we saw was to specialize std::vector to make it work on a slight modification of, here, Eigen::Vector4f, that is able to deal properly with this situation.
-</span>
+
 
 */
 
diff --git a/doc/StructHavingEigenMembers.dox b/doc/StructHavingEigenMembers.dox
index 7fbed0eb0..87016cdc9 100644
--- a/doc/StructHavingEigenMembers.dox
+++ b/doc/StructHavingEigenMembers.dox
@@ -6,7 +6,12 @@ namespace Eigen {
 
 \section StructHavingEigenMembers_summary Executive Summary
 
-If you define a structure having members of \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", you must overload its "operator new" so that it generates 16-bytes-aligned pointers. Fortunately, %Eigen provides you with a macro EIGEN_MAKE_ALIGNED_OPERATOR_NEW that does that for you.
+
+If you define a structure having members of \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types", you must ensure that calling operator new on it allocates properly aligned buffers.
+If you're compiling in \cpp17 mode only with a sufficiently recent compiler (e.g., GCC>=7, clang>=5, MSVC>=19.12), then everything is taken care by the compiler and you can stop reading.
+
+Otherwise, you have to overload its `operator new` so that it generates properly aligned pointers (e.g., 32-bytes-aligned for Vector4d and AVX).
+Fortunately, %Eigen provides you with a macro `EIGEN_MAKE_ALIGNED_OPERATOR_NEW` that does that for you.
 
 \section StructHavingEigenMembers_what What kind of code needs to be changed?
 
@@ -29,13 +34,13 @@ In other words: you have a class that has as a member a \ref TopicFixedSizeVecto
 
 \section StructHavingEigenMembers_how How should such code be modified?
 
-Very easy, you just need to put a EIGEN_MAKE_ALIGNED_OPERATOR_NEW macro in a public part of your class, like this:
+Very easy, you just need to put a `EIGEN_MAKE_ALIGNED_OPERATOR_NEW` macro in a public part of your class, like this:
 
 \code
 class Foo
 {
   ...
-  Eigen::Vector2d v;
+  Eigen::Vector4d v;
   ...
 public:
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
@@ -46,7 +51,9 @@ public:
 Foo *foo = new Foo;
 \endcode
 
-This macro makes "new Foo" always return an aligned pointer.
+This macro makes `new Foo` always return an aligned pointer.
+
+In \cpp17, this macro is empty.
 
 If this approach is too intrusive, see also the \ref StructHavingEigenMembers_othersolutions "other solutions".
 
@@ -58,7 +65,7 @@ OK let's say that your code looks like this:
 class Foo
 {
   ...
-  Eigen::Vector2d v;
+  Eigen::Vector4d v;
   ...
 };
 
@@ -67,45 +74,59 @@ class Foo
 Foo *foo = new Foo;
 \endcode
 
-A Eigen::Vector2d consists of 2 doubles, which is 128 bits. Which is exactly the size of a SSE packet, which makes it possible to use SSE for all sorts of operations on this vector. But SSE instructions (at least the ones that %Eigen uses, which are the fast ones) require 128-bit alignment. Otherwise you get a segmentation fault.
+A Eigen::Vector4d consists of 4 doubles, which is 256 bits.
+This is exactly the size of an AVX register, which makes it possible to use AVX for all sorts of operations on this vector.
+But AVX instructions (at least the ones that %Eigen uses, which are the fast ones) require 256-bit alignment.
+Otherwise you get a segmentation fault.
 
-For this reason, Eigen takes care by itself to require 128-bit alignment for Eigen::Vector2d, by doing two things:
-\li Eigen requires 128-bit alignment for the Eigen::Vector2d's array (of 2 doubles). With GCC, this is done with a __attribute__ ((aligned(16))).
-\li Eigen overloads the "operator new" of Eigen::Vector2d so it will always return 128-bit aligned pointers.
+For this reason, %Eigen takes care by itself to require 256-bit alignment for Eigen::Vector4d, by doing two things:
+\li %Eigen requires 256-bit alignment for the Eigen::Vector4d's array (of 4 doubles). With \cpp11 this is done with the <a href="https://en.cppreference.com/w/cpp/keyword/alignas">alignas</a> keyword, or compiler's extensions for c++98/03.
+\li %Eigen overloads the `operator new` of Eigen::Vector4d so it will always return 256-bit aligned pointers. (removed in \cpp17)
 
-Thus, normally, you don't have to worry about anything, Eigen handles alignment for you...
+Thus, normally, you don't have to worry about anything, %Eigen handles alignment of operator new for you...
 
-... except in one case. When you have a class Foo like above, and you dynamically allocate a new Foo as above, then, since Foo doesn't have aligned "operator new", the returned pointer foo is not necessarily 128-bit aligned.
+... except in one case. When you have a `class Foo` like above, and you dynamically allocate a new `Foo` as above, then, since `Foo` doesn't have aligned `operator new`, the returned pointer foo is not necessarily 256-bit aligned.
 
-The alignment attribute of the member v is then relative to the start of the class, foo. If the foo pointer wasn't aligned, then foo->v won't be aligned either!
+The alignment attribute of the member `v` is then relative to the start of the class `Foo`. If the `foo` pointer wasn't aligned, then `foo->v` won't be aligned either!
 
-The solution is to let class Foo have an aligned "operator new", as we showed in the previous section.
+The solution is to let `class Foo` have an aligned `operator new`, as we showed in the previous section.
+
+This explanation also holds for SSE/NEON/MSA/Altivec/VSX targets, which require 16-bytes alignment, and AVX512 which requires 64-bytes alignment for fixed-size objects multiple of 64 bytes (e.g., Eigen::Matrix4d).
 
 \section StructHavingEigenMembers_movetotop Should I then put all the members of Eigen types at the beginning of my class?
 
-That's not required. Since Eigen takes care of declaring 128-bit alignment, all members that need it are automatically 128-bit aligned relatively to the class. So code like this works fine:
+That's not required. Since %Eigen takes care of declaring adequate alignment, all members that need it are automatically aligned relatively to the class. So code like this works fine:
 
 \code
 class Foo
 {
   double x;
-  Eigen::Vector2d v;
+  Eigen::Vector4d v;
 public:
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
 };
 \endcode
 
+That said, as usual, it is recommended to sort the members so that alignment does not waste memory.
+In the above example, with AVX, the compiler will have to reserve 24 empty bytes between `x` and `v`.
+
+
 \section StructHavingEigenMembers_dynamicsize What about dynamic-size matrices and vectors?
 
 Dynamic-size matrices and vectors, such as Eigen::VectorXd, allocate dynamically their own array of coefficients, so they take care of requiring absolute alignment automatically. So they don't cause this issue. The issue discussed here is only with \ref TopicFixedSizeVectorizable  "fixed-size vectorizable matrices and vectors".
 
+
 \section StructHavingEigenMembers_bugineigen So is this a bug in Eigen?
 
-No, it's not our bug. It's more like an inherent problem of the C++98 language specification, and seems to be taken care of in the upcoming language revision: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2341.pdf">see this document</a>.
+No, it's not our bug. It's more like an inherent problem of the c++ language specification that has been solved in c++17 through the feature known as <a href="http://wg21.link/p0035r4">dynamic memory allocation for over-aligned data</a>.
+
 
-\section StructHavingEigenMembers_conditional What if I want to do this conditionnally (depending on template parameters) ?
+\section StructHavingEigenMembers_conditional What if I want to do this conditionally (depending on template parameters) ?
 
-For this situation, we offer the macro EIGEN_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign). It will generate aligned operators like EIGEN_MAKE_ALIGNED_OPERATOR_NEW if NeedsToAlign is true. It will generate operators with the default alignment if NeedsToAlign is false.
+For this situation, we offer the macro `EIGEN_MAKE_ALIGNED_OPERATOR_NEW_IF(NeedsToAlign)`.
+It will generate aligned operators like `EIGEN_MAKE_ALIGNED_OPERATOR_NEW` if `NeedsToAlign` is true.
+It will generate operators with the default alignment if `NeedsToAlign` is false.
+In \cpp17, this macro is empty.
 
 Example:
 
@@ -130,7 +151,7 @@ Foo<3> *foo3 = new Foo<3>; // foo3 has only the system default alignment guarant
 
 \section StructHavingEigenMembers_othersolutions Other solutions
 
-In case putting the EIGEN_MAKE_ALIGNED_OPERATOR_NEW macro everywhere is too intrusive, there exists at least two other solutions.
+In case putting the `EIGEN_MAKE_ALIGNED_OPERATOR_NEW` macro everywhere is too intrusive, there exists at least two other solutions.
 
 \subsection othersolutions1 Disabling alignment
 
@@ -139,22 +160,13 @@ The first is to disable alignment requirement for the fixed size members:
 class Foo
 {
   ...
-  Eigen::Matrix<double,2,1,Eigen::DontAlign> v;
+  Eigen::Matrix<double,4,1,Eigen::DontAlign> v;
   ...
 };
 \endcode
-This has for effect to disable vectorization when using \c v.
-If a function of Foo uses it several times, then it still possible to re-enable vectorization by copying it into an aligned temporary vector:
-\code
-void Foo::bar()
-{
-  Eigen::Vector2d av(v);
-  // use av instead of v
-  ...
-  // if av changed, then do:
-  v = av;
-}
-\endcode
+This `v` is fully compatible with aligned Eigen::Vector4d.
+This has only for effect to make load/stores to `v` more expensive (usually slightly, but that's hardware dependent).
+
 
 \subsection othersolutions2 Private structure
 
@@ -164,7 +176,7 @@ The second consist in storing the fixed-size objects into a private struct which
 struct Foo_d
 {
   EIGEN_MAKE_ALIGNED_OPERATOR_NEW
-  Vector2d v;
+  Vector4d v;
   ...
 };
 
@@ -183,7 +195,8 @@ private:
 };
 \endcode
 
-The clear advantage here is that the class Foo remains unchanged regarding alignment issues. The drawback is that a heap allocation will be required whatsoever.
+The clear advantage here is that the class `Foo` remains unchanged regarding alignment issues.
+The drawback is that an additional heap allocation will be required whatsoever.
 
 */
 
diff --git a/doc/UnalignedArrayAssert.dox b/doc/UnalignedArrayAssert.dox
index 8676faa1b..410c8a58f 100644
--- a/doc/UnalignedArrayAssert.dox
+++ b/doc/UnalignedArrayAssert.dox
@@ -12,7 +12,9 @@ is explained here: http://eigen.tuxfamily.org/dox-devel/group__TopicUnalignedArr
 **** READ THIS WEB PAGE !!! ****"' failed.
 </pre>
 
-There are 4 known causes for this issue. Please read on to understand them and learn how to fix them.
+There are 4 known causes for this issue.
+If you can target \cpp17 only with a recent compiler (e.g., GCC>=7, clang>=5, MSVC>=19.12), then you're lucky: enabling c++17 should be enough (if not, please <a href="http://eigen.tuxfamily.org/bz/">report</a> to us).
+Otherwise, please read on to understand those issues and learn how to fix them.
 
 \eigenAutoToc
 
@@ -35,7 +37,7 @@ If you have code like this,
 class Foo
 {
   //...
-  Eigen::Vector2d v;
+  Eigen::Vector4d v;
   //...
 };
 //...
@@ -44,27 +46,27 @@ Foo *foo = new Foo;
 
 then you need to read this separate page: \ref TopicStructHavingEigenMembers "Structures Having Eigen Members".
 
-Note that here, Eigen::Vector2d is only used as an example, more generally the issue arises for all \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types".
+Note that here, Eigen::Vector4d is only used as an example, more generally the issue arises for all \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types".
 
 \section c2 Cause 2: STL Containers or manual memory allocation
 
 If you use STL Containers such as std::vector, std::map, ..., with %Eigen objects, or with classes containing %Eigen objects, like this,
 
 \code
-std::vector<Eigen::Matrix2f> my_vector;
-struct my_class { ... Eigen::Matrix2f m; ... };
+std::vector<Eigen::Matrix2d> my_vector;
+struct my_class { ... Eigen::Matrix2d m; ... };
 std::map<int, my_class> my_map;
 \endcode
 
 then you need to read this separate page: \ref TopicStlContainers "Using STL Containers with Eigen".
 
-Note that here, Eigen::Matrix2f is only used as an example, more generally the issue arises for all \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types" and \ref TopicStructHavingEigenMembers "structures having such Eigen objects as member".
+Note that here, Eigen::Matrix2d is only used as an example, more generally the issue arises for all \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types" and \ref TopicStructHavingEigenMembers "structures having such Eigen objects as member".
 
-The same issue will be exhibited by any classes/functions by-passing operator new to allocate memory, that is, by performing custom memory allocation followed by calls to the placement new operator. This is for instance typically the case of \c std::make_shared or \c std::allocate_shared for which is the solution is to use an \ref aligned_allocator "aligned allocator" as detailed in the \ref TopicStlContainers "solution for STL containers".
+The same issue will be exhibited by any classes/functions by-passing operator new to allocate memory, that is, by performing custom memory allocation followed by calls to the placement new operator. This is for instance typically the case of \c `std::make_shared` or `std::allocate_shared` for which is the solution is to use an \ref aligned_allocator "aligned allocator" as detailed in the \ref TopicStlContainers "solution for STL containers".
 
 \section c3 Cause 3: Passing Eigen objects by value
 
-If some function in your code is getting an Eigen object passed by value, like this,
+If some function in your code is getting an %Eigen object passed by value, like this,
 
 \code
 void func(Eigen::Vector4d v);
@@ -90,11 +92,13 @@ then you need to read this separate page: \ref TopicWrongStackAlignment "Compile
 
 Note that here, Eigen::Quaternionf is only used as an example, more generally the issue arises for all \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen types".
 
+
 \section explanation General explanation of this assertion
 
-\ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen objects" must absolutely be created at 16-byte-aligned locations, otherwise SIMD instructions addressing them will crash.
+\ref TopicFixedSizeVectorizable "Fixed-size vectorizable Eigen objects" must absolutely be created at properly aligned locations, otherwise SIMD instructions addressing them will crash.
+For instance, SSE/NEON/MSA/Altivec/VSX targets will require 16-byte-alignment, whereas AVX and AVX512 targets may require up to 32 and 64 byte alignment respectively.
 
-Eigen normally takes care of these alignment issues for you, by setting an alignment attribute on them and by overloading their "operator new".
+%Eigen normally takes care of these alignment issues for you, by setting an alignment attribute on them and by overloading their `operator new`.
 
 However there are a few corner cases where these alignment settings get overridden: they are the possible causes for this assertion.
 
@@ -102,22 +106,22 @@ However there are a few corner cases where these alignment settings get overridd
 
 Three possibilities:
 <ul>
-  <li>Use the \c DontAlign option to Matrix, Array, Quaternion, etc. objects that gives you trouble. This way Eigen won't try to align them, and thus won"t assume any special alignment. On the down side, you will pay the cost of unaligned loads/stores for them, but on modern CPUs, the overhead is either null or marginal. See \link StructHavingEigenMembers_othersolutions here \endlink for an example.</li>
-  <li>Define \link TopicPreprocessorDirectivesPerformance EIGEN_DONT_ALIGN_STATICALLY \endlink. That disables all 16-byte (and above) static alignment code, while keeping 16-byte (or above) heap alignment. This has the effect of
+  <li>Use the \c DontAlign option to Matrix, Array, Quaternion, etc. objects that gives you trouble. This way %Eigen won't try to over-align them, and thus won"t assume any special alignment. On the down side, you will pay the cost of unaligned loads/stores for them, but on modern CPUs, the overhead is either null or marginal. See \link StructHavingEigenMembers_othersolutions here \endlink for an example.</li>
+  <li>Define \link TopicPreprocessorDirectivesPerformance EIGEN_MAX_STATIC_ALIGN_BYTES \endlink to 0. That disables all 16-byte (and above) static alignment code, while keeping 16-byte (or above) heap alignment. This has the effect of
       vectorizing fixed-size objects (like Matrix4d) through unaligned stores (as controlled by \link TopicPreprocessorDirectivesPerformance EIGEN_UNALIGNED_VECTORIZE \endlink), while keeping unchanged the vectorization of dynamic-size objects
-      (like MatrixXd). But do note that this breaks ABI compatibility with the default behavior of static alignment.</li>
-  <li>Or define both \link TopicPreprocessorDirectivesPerformance  EIGEN_DONT_VECTORIZE \endlink and EIGEN_DISABLE_UNALIGNED_ARRAY_ASSERT. This keeps the
-      16-byte alignment code and thus preserves ABI compatibility, but completely disables vectorization.</li>
+      (like MatrixXd). On 64 bytes systems, you might also define it 16 to disable only 32 and 64 bytes of over-alignment. But do note that this breaks ABI compatibility with the default behavior of static alignment.</li>
+  <li>Or define both \link TopicPreprocessorDirectivesPerformance  EIGEN_DONT_VECTORIZE \endlink and `EIGEN_DISABLE_UNALIGNED_ARRAY_ASSERT`. This keeps the
+      16-byte (or above) alignment code and thus preserves ABI compatibility, but completely disables vectorization.</li>
 </ul>
 
-If you want to know why defining EIGEN_DONT_VECTORIZE does not by itself disable 16-byte alignment and the assertion, here's the explanation:
+If you want to know why defining `EIGEN_DONT_VECTORIZE` does not by itself disable 16-byte (or above) alignment and the assertion, here's the explanation:
 
 It doesn't disable the assertion, because otherwise code that runs fine without vectorization would suddenly crash when enabling vectorization.
-It doesn't disable 16-byte alignment, because that would mean that vectorized and non-vectorized code are not mutually ABI-compatible. This ABI compatibility is very important, even for people who develop only an in-house application, as for instance one may want to have in the same application a vectorized path and a non-vectorized path.
+It doesn't disable 16-byte (or above) alignment, because that would mean that vectorized and non-vectorized code are not mutually ABI-compatible. This ABI compatibility is very important, even for people who develop only an in-house application, as for instance one may want to have in the same application a vectorized path and a non-vectorized path.
 
 \section checkmycode How can I check my code is safe regarding alignment issues?
 
-Unfortunately, there is no possibility in C++ to detect any of the aforementioned shortcoming at compile time (though static analysers are becoming more and more powerful and could detect some of them).
+Unfortunately, there is no possibility in c++ to detect any of the aforementioned shortcoming at compile time (though static analyzers are becoming more and more powerful and could detect some of them).
 Even at runtime, all we can do is to catch invalid unaligned allocation and trigger the explicit assertion mentioned at the beginning of this page.
 Therefore, if your program runs fine on a given system with some given compilation flags, then this does not guarantee that your code is safe. For instance, on most 64 bits systems buffer are aligned on 16 bytes boundary and so, if you do not enable AVX instruction set, then your code will run fine. On the other hand, the same code may assert if moving to a more exotic platform, or enabling AVX instructions that required 32 bytes alignment by default.