perf(math): use checked MKL GER for rank-one products

src/fesa/math/dense_blas_internal.cpp

@@ -127,7 +127,24 @@ Matrix MultiplyTransposeLeft(const Matrix& left, const Matrix& right) {
 bool OuterProduct(const double* left, const std::size_t rows,
                   const double* right, const std::size_t columns,
                   double* destination) {
-  return MultiplyTransposeRight(left, rows, right, columns, 1U, destination);
+  const auto m = ToMklSize(rows);
+  const auto n = ToMklSize(columns);
+  const auto maximum = std::numeric_limits<std::size_t>::max() / sizeof(double);
+  if (!m.HasValue() || !n.HasValue() || rows > maximum || columns > maximum ||
+      (columns != 0U && rows > maximum / columns))
+    throw std::length_error{"Dense product dimensions exceed backend limits."};
+  if (rows == 0U || columns == 0U) return true;
+  if (destination == nullptr || left == nullptr || right == nullptr)
+    throw std::invalid_argument{"Dense product requires nonnull storage."};
+  for (std::size_t i = 0U; i < rows; ++i)
+    if (!std::isfinite(left[i])) return false;
+  for (std::size_t i = 0U; i < columns; ++i)
+    if (!std::isfinite(right[i])) return false;
+  // GER updates A, so replace every destination entry only after validation.
+  std::fill_n(destination, rows * columns, 0.0);
+  cblas_dger(CblasRowMajor, m.Value(), n.Value(), 1.0, left, 1, right, 1,
+             destination, n.Value());
+  return true;
 }
 
 bool MultiplyTransposeRight(const double* left, const std::size_t rows,