convert linalg library from Fortran to C++

lib/linalg/dlamch.cpp

@@ -0,0 +1,45 @@
+
+#include <cctype>
+#include <limits>
+
+extern "C" {
+
+#include "lmp_f2c.h"
+
+// undefine conflicting f2c macros
+#undef min
+#undef max
+
+doublereal dlamch_(const char *cmach)
+{
+  if (!cmach) return 0.0;
+  char select = toupper(*cmach);
+
+  // BLAS assumes rounding not truncation => epsilon is half
+  const double eps = 0.5 * std::numeric_limits<double>::epsilon();
+  if (select == 'E') return eps;
+
+  double min = std::numeric_limits<double>::min();
+  const double max = std::numeric_limits<double>::max();
+  double small = 1.0 / max;
+  if (small >= min) min = small * (1.0 + eps);
+  if (select == 'S') return min;
+
+  const double radix = std::numeric_limits<double>::radix;
+  if (select == 'B') return radix;
+
+  if (select == 'P') return eps * radix;
+
+  if (select == 'N') return std::numeric_limits<double>::digits;
+
+  if (select == 'M') return std::numeric_limits<double>::min_exponent;
+
+  if (select == 'U') return min;
+
+  if (select == 'L') return std::numeric_limits<double>::max_exponent;
+
+  if (select == 'O') return max;
+
+  return 0.0;
+}
+}