diff --git a/.gitignore b/.gitignore
index 1dae78f..76cab79 100644
--- a/.gitignore
+++ b/.gitignore
@@ -83,3 +83,5 @@ docs_build/xml-matlab
 docs_build/sphinx/_doxygen
 toolbox/lib/cmake-build-debug
 toolbox/cmake-build-debug
+
+/Xcode
diff --git a/src/SplineConstant.cc b/src/SplineConstant.cc
index e123f9a..1296725 100644
--- a/src/SplineConstant.cc
+++ b/src/SplineConstant.cc
@@ -72,8 +72,8 @@ namespace Splines {
   //! Evalute spline value at `x`
   real_type
   ConstantSpline::eval( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return m_Y[res.first];
   }
 
diff --git a/src/SplineCubicBase.cc b/src/SplineCubicBase.cc
index e42545a..06d1871 100644
--- a/src/SplineCubicBase.cc
+++ b/src/SplineCubicBase.cc
@@ -136,8 +136,8 @@ namespace Splines {
 
   real_type
   CubicSplineBase::eval( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_eval( res.first, res.second );
   }
 
@@ -160,8 +160,8 @@ namespace Splines {
 
   real_type
   CubicSplineBase::D( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_D( res.first, res.second );
   }
 
@@ -184,8 +184,8 @@ namespace Splines {
 
   real_type
   CubicSplineBase::DD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DD( res.first, res.second );
   }
 
@@ -208,8 +208,8 @@ namespace Splines {
 
   real_type
   CubicSplineBase::DDD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DDD( res.first, res.second );
   }
 
diff --git a/src/SplineLinear.cc b/src/SplineLinear.cc
index a4cbf15..a1e628b 100644
--- a/src/SplineLinear.cc
+++ b/src/SplineLinear.cc
@@ -46,8 +46,8 @@ namespace Splines {
 
   real_type
   LinearSpline::eval( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_eval( res.first, res.second );
   }
 
@@ -64,8 +64,8 @@ namespace Splines {
     if ( m_curve_can_extend && m_curve_extended_constant ) {
       if ( x <= m_X[0] || x >= m_X[m_npts-1] ) return 0;
     }
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_D( res.first, res.second );
   }
 
diff --git a/src/SplineQuinticBase.cc b/src/SplineQuinticBase.cc
index fb25c55..1ae6376 100644
--- a/src/SplineQuinticBase.cc
+++ b/src/SplineQuinticBase.cc
@@ -105,8 +105,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::eval( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_eval( res.first, res.second );
   }
 
@@ -130,8 +130,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::D( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_D( res.first, res.second );
   }
 
@@ -155,8 +155,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::DD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DD( res.first, res.second );
   }
 
@@ -180,8 +180,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::DDD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DDD( res.first, res.second );
   }
 
@@ -205,8 +205,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::DDDD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DDDD( res.first, res.second );
   }
 
@@ -230,8 +230,8 @@ namespace Splines {
 
   real_type
   QuinticSplineBase::DDDDD( real_type x ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     return this->id_DDDDD( res.first, res.second );
   }
 
diff --git a/src/SplineSet.cc b/src/SplineSet.cc
index b09209d..53564ab 100644
--- a/src/SplineSet.cc
+++ b/src/SplineSet.cc
@@ -45,12 +45,14 @@ namespace Splines {
     size_t U{ data.size() };
     size_t L{ 0 };
     while ( U-L > 1 ) {
-      size_t pos{ (L+U)>>1 };
-      std::string const & id_pos = data[pos].first;
+      size_t pos{ (L+U)>>1 }; // se L=U+1 --> (L+U)/2 ==> L
+      std::string const & id_pos{ data[pos].first };
       if ( id_pos < id ) L = pos; else U = pos;
     }
     if ( data[L].first == id ) return data[L].second;
-    if ( data[U].first == id ) return data[U].second;
+    if ( U < data.size() )
+      if ( data[U].first == id )
+        return data[U].second;
     return -1; // non trovato
   }
 
@@ -61,7 +63,7 @@ namespace Splines {
     size_t pos{ data.size() };
     data.push_back(DATA_TYPE(id,position));
     while ( pos > 0 ) {
-      size_t pos1 = pos-1;
+      size_t pos1{pos-1};
       data[pos].first  = data[pos1].first;
       data[pos].second = data[pos1].second;
       if ( data[pos1].first < id ) break;
diff --git a/src/SplineSetGC.cc b/src/SplineSetGC.cc
index 26337b1..4a4b7eb 100644
--- a/src/SplineSetGC.cc
+++ b/src/SplineSetGC.cc
@@ -346,7 +346,7 @@ namespace Splines {
     real_type x;
     intersect( indep, zeta, x );
     for ( integer pos{0}; pos < m_header_to_position.n_elem(); ++pos ) {
-      BinarySearch::DATA_TYPE const & D = m_header_to_position.get_elem( pos );
+      BinarySearch::DATA_TYPE const & D{ m_header_to_position.get_elem( pos ) };
       vals[D.first] = m_splines[size_t(D.second)]->eval(x);
     }
   }
@@ -367,7 +367,7 @@ namespace Splines {
 
     // preallocation
     for ( integer pos{0}; pos < m_header_to_position.n_elem(); ++pos ) {
-      BinarySearch::DATA_TYPE const & D = m_header_to_position.get_elem( pos );
+      BinarySearch::DATA_TYPE const & D{ m_header_to_position.get_elem( pos ) };
       vals[D.first].set_vec_real(unsigned(npts));
     }
 
diff --git a/src/SplineVec.cc b/src/SplineVec.cc
index 420f334..32222ed 100644
--- a/src/SplineVec.cc
+++ b/src/SplineVec.cc
@@ -57,7 +57,7 @@ namespace Splines {
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
   void
-  SplineVec::search( real_type x, std::pair<integer,real_type> & res ) const {
+  SplineVec::search( std::pair<integer,real_type> & res ) const {
     UTILS_ASSERT( m_npts > 0, "in SplineVec[{}]::search(...), npts == 0!", m_name );
     #ifdef SPLINES_USE_THREADS
     bool ok{true};
@@ -69,13 +69,12 @@ namespace Splines {
     Utils::search_interval(
       m_npts,
       m_X,
-      x,
+      res.second,
       last_interval,
       m_curve_is_closed,
       m_curve_can_extend
     );
-    res.first  = last_interval;
-    res.second = x;
+    res.first = last_interval;
   }
 
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -286,8 +285,8 @@ namespace Splines {
 
   real_type
   SplineVec::eval( real_type x, integer j ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base[4];
     integer i{res.first};
     Hermite3( res.second-m_X[i], m_X[i+1]-m_X[i], base );
@@ -301,8 +300,8 @@ namespace Splines {
 
   real_type
   SplineVec::D( real_type x, integer j ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_D[4];
     integer i{res.first};
     Hermite3_D( res.second-m_X[i], m_X[i+1]-m_X[i], base_D );
@@ -316,8 +315,8 @@ namespace Splines {
 
   real_type
   SplineVec::DD( real_type x, integer j ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_DD[4];
     integer i{res.first};
     Hermite3_DD( res.second-m_X[i], m_X[i+1]-m_X[i], base_DD );
@@ -331,8 +330,8 @@ namespace Splines {
 
   real_type
   SplineVec::DDD( real_type x, integer j ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_DDD[4];
     integer i{res.first};
     Hermite3_DDD( res.second-m_X[i], m_X[i+1]-m_X[i], base_DDD );
@@ -350,8 +349,8 @@ namespace Splines {
     real_type vals[],
     integer   inc
   ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base[4];
     integer i{res.first};
     Hermite3( res.second-m_X[i], m_X[i+1]-m_X[i], base );
@@ -371,8 +370,8 @@ namespace Splines {
     real_type vals[],
     integer   inc
   ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_D[4];
     integer i{res.first};
     Hermite3_D( res.second-m_X[i], m_X[i+1]-m_X[i], base_D );
@@ -392,8 +391,8 @@ namespace Splines {
     real_type vals[],
     integer   inc
   ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_DD[4];
     integer i{res.first};
     Hermite3_DD( res.second-m_X[i], m_X[i+1]-m_X[i], base_DD );
@@ -413,8 +412,8 @@ namespace Splines {
     real_type vals[],
     integer   inc
   ) const {
-    std::pair<integer,real_type> res;
-    this->search( x, res );
+    std::pair<integer,real_type> res(0,x);
+    this->search( res );
     real_type base_DDD[4];
     integer i{res.first};
     Hermite3_DDD( res.second-m_X[i], m_X[i+1]-m_X[i], base_DDD );
diff --git a/src/Splines.cc b/src/Splines.cc
index f50fbdc..c5d3978 100644
--- a/src/Splines.cc
+++ b/src/Splines.cc
@@ -238,7 +238,7 @@ namespace Splines {
   // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
   void
-  Spline::search( real_type x, std::pair<integer,real_type> & res ) const {
+  Spline::search( std::pair<integer,real_type> & res ) const {
     UTILS_ASSERT( m_npts > 0, "in Spline[{}]::search(...), npts == 0!", m_name );
     #ifdef SPLINES_USE_THREADS
     bool ok{true};
@@ -250,13 +250,12 @@ namespace Splines {
     Utils::search_interval(
       m_npts,
       m_X,
-      x,
+      res.second,
       last_interval,
       m_curve_is_closed,
       m_curve_can_extend
     );
-    res.first  = last_interval;
-    res.second = x;
+    res.first = last_interval;
   }
 
   void
diff --git a/src/Splines.hh b/src/Splines.hh
index 8007870..64959d3 100644
--- a/src/Splines.hh
+++ b/src/Splines.hh
@@ -415,7 +415,7 @@ namespace Splines {
     //!
     //! Find interval containing `x` using binary search.
     //!
-    void search( real_type x, std::pair<integer,real_type> & res ) const;
+    void search( std::pair<integer,real_type> & res ) const;
 
     //!
     //! \name Open/Close
diff --git a/src/Splines/SplineVec.hxx b/src/Splines/SplineVec.hxx
index 3ece017..817702c 100644
--- a/src/Splines/SplineVec.hxx
+++ b/src/Splines/SplineVec.hxx
@@ -85,7 +85,7 @@ namespace Splines {
     //!
     //! Search the segment containing `x`
     //!
-    void search( real_type x, std::pair<integer,real_type> & res ) const;
+    void search( std::pair<integer,real_type> & res ) const;
 
     //!
     //! Spline name usd in the constructor