LAPACK CPU time functions.

lapack/CMakeLists.txt

diff --git a/lapack/CMakeLists.txt b/lapack/CMakeLists.txt
index 8d6d754..1babd13 100644
--- a/lapack/CMakeLists.txt
+++ b/lapack/CMakeLists.txt
@@ -22,7 +22,7 @@
 include_directories(../blas)
 
 set(EigenLapack_SRCS
-single.cpp double.cpp complex_single.cpp complex_double.cpp ../blas/xerbla.cpp
+  dsecnd_INT_CPU_TIME.cpp second_INT_CPU_TIME.cpp single.cpp double.cpp complex_single.cpp complex_double.cpp ../blas/xerbla.cpp
 )
 
 if(EIGEN_Fortran_COMPILER_WORKS)
@@ -38,7 +38,6 @@
   dlapy2.f  dlapy3.f  slapy2.f  slapy3.f
   clacgv.f  zlacgv.f
   slamch.f  dlamch.f
-  second_NONE.f dsecnd_NONE.f
 )
 
 option(EIGEN_ENABLE_LAPACK_TESTS OFF "Enable the Lapack unit tests")

lapack/dsecnd_INT_CPU_TIME.cpp

diff --git a/lapack/dsecnd_INT_CPU_TIME.cpp b/lapack/dsecnd_INT_CPU_TIME.cpp
new file mode 100644
index 0000000..5052136
--- /dev/null
+++ b/lapack/dsecnd_INT_CPU_TIME.cpp
@@ -0,0 +1,36 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2024 The Eigen Authors
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifdef _WIN32
+#include <cstdint>
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#else
+#include <ctime>
+#endif
+
+extern "C" {
+double dsecnd_();
+}
+
+// Elapsed CPU Time in seconds.
+double dsecnd_() {
+#ifdef _WIN32
+  // GetProcessTimes() uses 100-nanosecond time units.
+  FILETIME creation_time, exit_time, kernel_time, user_time;
+  GetProcessTimes(GetCurrentProcess(), &creation_time, &exit_time, &kernel_time, &user_time);
+  ULARGE_INTEGER user;
+  user.HighPart = user_time.dwHighDateTime;
+  user.LowPart = user_time.dwLowDateTime;
+  uint64_t time_100ns = user.QuadPart;
+  return static_cast<double>(time_100ns) / 10000000.0;
+#else
+  return static_cast<double>(std::clock()) / static_cast<double>(CLOCKS_PER_SEC);
+#endif
+}

lapack/second_INT_CPU_TIME.cpp

diff --git a/lapack/second_INT_CPU_TIME.cpp b/lapack/second_INT_CPU_TIME.cpp
new file mode 100644
index 0000000..07231a3
--- /dev/null
+++ b/lapack/second_INT_CPU_TIME.cpp
@@ -0,0 +1,36 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2024 The Eigen Authors
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifdef _WIN32
+#include <cstdint>
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#else
+#include <ctime>
+#endif
+
+extern "C" {
+float second_();
+}
+
+// Elapsed CPU Time in seconds.
+float second_() {
+#ifdef _WIN32
+  // GetProcessTimes() uses 100-nanosecond time units.
+  FILETIME creation_time, exit_time, kernel_time, user_time;
+  GetProcessTimes(GetCurrentProcess(), &creation_time, &exit_time, &kernel_time, &user_time);
+  ULARGE_INTEGER user;
+  user.HighPart = user_time.dwHighDateTime;
+  user.LowPart = user_time.dwLowDateTime;
+  uint64_t time_100ns = user.QuadPart;
+  return static_cast<float>(time_100ns) / 10000000.0f;
+#else
+  return static_cast<float>(std::clock()) / static_cast<float>(CLOCKS_PER_SEC);
+#endif
+}