Move max_align_t handling into jet.h
This was currently buried in port.h. Since there is exactly one use
of the max_align_t handling, it is better from a readability
and cleanliness perspective to have this in jet.h.
Change-Id: I2f3dde75df7c333bd95393b9e4fc4cd5160d6afb
diff --git a/include/ceres/internal/port.h b/include/ceres/internal/port.h
index 9aa041a..d69d8c5 100644
--- a/include/ceres/internal/port.h
+++ b/include/ceres/internal/port.h
@@ -32,8 +32,6 @@
#define CERES_PUBLIC_INTERNAL_PORT_H_
// This file needs to compile as c code.
-#ifdef __cplusplus
-#include <cstddef>
#include "ceres/internal/config.h"
#if defined(CERES_USE_OPENMP)
@@ -56,33 +54,6 @@
# error One of CERES_USE_OPENMP, CERES_USE_TBB,CERES_USE_CXX11_THREADS or CERES_NO_THREADS must be defined.
#endif
-namespace ceres {
-
-// We allocate some Eigen objects on the stack and other places they
-// might not be aligned to X(=16 [SSE], 32 [AVX] etc)-byte boundaries. If we
-// have C++11, we can specify their alignment (which is desirable, as it means
-// we can safely enable vectorisation on matrices). However, the standard gives
-// wide lattitude as to what alignments are legal. It must be the case that
-// alignments up to alignof(std::max_align_t) are valid, but this might be < 16
-// on some platforms, in which case even if using C++11, on these platforms
-// we should not attempt to align to X-byte boundaries. If using < C++11,
-// we cannot specify the alignment.
-namespace port_constants {
-static constexpr size_t kMaxAlignBytes =
- // Work around a GCC 4.8 bug
- // (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56019) where
- // std::max_align_t is misplaced.
-#if defined (__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 8
- alignof(::max_align_t);
-#else
- alignof(std::max_align_t);
-#endif
-} // namespace port_constants
-
-} // namespace ceres
-
-#endif // __cplusplus
-
// A macro to signal which functions and classes are exported when
// building a DLL with MSVC.
//
diff --git a/include/ceres/jet.h b/include/ceres/jet.h
index 7eb199a..2106357 100644
--- a/include/ceres/jet.h
+++ b/include/ceres/jet.h
@@ -258,21 +258,28 @@
// supported is < 16, in which case we do not specify an alignment, as this
// implies the host is not a modern x86 machine. If using < C++11, we cannot
// specify alignment.
+
#if defined(EIGEN_DONT_VECTORIZE)
- // Without >= C++11, we cannot specify the alignment so fall back to safe,
- // unvectorised version.
Eigen::Matrix<T, N, 1, Eigen::DontAlign> v;
#else
// Enable vectorisation iff the maximum supported scalar alignment is >=
// 16 bytes, as this is the minimum required by Eigen for any vectorisation.
//
// NOTE: It might be the case that we could get >= 16-byte alignment even if
- // kMaxAlignBytes < 16. However we can't guarantee that this
+ // max_align_t < 16. However we can't guarantee that this
// would happen (and it should not for any modern x86 machine) and if it
// didn't, we could get misaligned Jets.
static constexpr int kAlignOrNot =
- 16 <= ::ceres::port_constants::kMaxAlignBytes
- ? Eigen::AutoAlign : Eigen::DontAlign;
+ // Work around a GCC 4.8 bug
+ // (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56019) where
+ // std::max_align_t is misplaced.
+#if defined (__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 8
+ alignof(::max_align_t) >= 16
+#else
+ alignof(std::max_align_t) >= 16
+#endif
+ ? Eigen::AutoAlign : Eigen::DontAlign;
+
#if defined(EIGEN_MAX_ALIGN_BYTES)
// Eigen >= 3.3 supports AVX & FMA instructions that require 32-byte alignment
// (greater for AVX512). Rather than duplicating the detection logic, use
@@ -287,11 +294,13 @@
// Eigen < 3.3 only supported 16-byte alignment.
#define CERES_JET_ALIGN_BYTES 16
#endif
+
// Default to the native alignment if 16-byte alignment is not guaranteed to
// be supported. We cannot use alignof(T) as if we do, GCC 4.8 complains that
// the alignment 'is not an integer constant', although Clang accepts it.
static constexpr size_t kAlignment = kAlignOrNot == Eigen::AutoAlign
? CERES_JET_ALIGN_BYTES : alignof(double);
+
#undef CERES_JET_ALIGN_BYTES
alignas(kAlignment) Eigen::Matrix<T, N, 1, kAlignOrNot> v;
#endif
