Make PixelChanneldentifier::thePacking constexpr

DataFormats/SiPixelDetId/interface/PixelChannelIdentifier.h

@@ -4,29 +4,17 @@
 #include <utility>
 #include "FWCore/Utilities/interface/GCC11Compatibility.h"
 
-class PixelChannelIdentifier {
-public:
-  typedef unsigned int PackedDigiType;
-  typedef unsigned int ChannelType;
-
-  static std::pair<int, int> channelToPixel(int ch) {
-    int row = (ch >> thePacking.column_width) & thePacking.row_mask;
-    int col = ch & thePacking.column_mask;
-    return std::pair<int, int>(row, col);
-  }
-
-  static int pixelToChannel(int row, int col) { return (row << thePacking.column_width) | col; }
-
+namespace pixelchanelidentifierimpl {
   /**
    * Pack the pixel information to use less memory
    */
 
   class Packing {
   public:
+    using PackedDigiType = unsigned int;
+
     // Constructor: pre-computes masks and shifts from field widths
-    // gcc4.8: sorry, unimplemented: use of the value of the object being constructed in a constant expression
-    // no constexpr yet....
-    Packing(unsigned int row_w, unsigned int column_w, unsigned int time_w, unsigned int adc_w)
+    constexpr Packing(unsigned int row_w, unsigned int column_w, unsigned int time_w, unsigned int adc_w)
         : row_width(row_w),
           column_width(column_w),
           adc_width(adc_w),
@@ -43,37 +31,46 @@ class PixelChannelIdentifier {
           max_column(column_mask),
           max_adc(adc_mask) {}
 
-    int row_width;
-    int column_width;
-    int adc_width;
+    const int row_width;
+    const int column_width;
+    const int adc_width;
 
-    int row_shift;
-    int column_shift;
-    int time_shift;
-    int adc_shift;
+    const int row_shift;
+    const int column_shift;
+    const int time_shift;
+    const int adc_shift;
 
-    PackedDigiType row_mask;
-    PackedDigiType column_mask;
-    PackedDigiType time_mask;
-    PackedDigiType adc_mask;
-    PackedDigiType rowcol_mask;
+    const PackedDigiType row_mask;
+    const PackedDigiType column_mask;
+    const PackedDigiType time_mask;
+    const PackedDigiType adc_mask;
+    const PackedDigiType rowcol_mask;
 
-    int max_row;
-    int max_column;
-    int max_adc;
+    const int max_row;
+    const int max_column;
+    const int max_adc;
   };
+}  // namespace pixelchanelidentifierimpl
 
+class PixelChannelIdentifier {
 public:
-  //#ifndef CMS_NOCXX11
-  static Packing packing() { return Packing(8, 9, 4, 11); }
+  typedef unsigned int PackedDigiType;
+  typedef unsigned int ChannelType;
 
-  static const Packing thePacking;
+  static std::pair<int, int> channelToPixel(int ch) {
+    int row = (ch >> thePacking.column_width) & thePacking.row_mask;
+    int col = ch & thePacking.column_mask;
+    return std::pair<int, int>(row, col);
+  }
+
+  static int pixelToChannel(int row, int col) { return (row << thePacking.column_width) | col; }
+
+  using Packing = pixelchanelidentifierimpl::Packing;
 
-  //#else
-  //static constexpr Packing packing() { return Packing(8, 9, 4, 11);}
+public:
+  constexpr static Packing packing() { return Packing(8, 9, 4, 11); }
 
-  //static constexpr Packing thePacking = packing();
-  //#endif
+  constexpr static Packing thePacking = {11, 11, 0, 10};
 };
 
 #endif