From b08f89e68ade22c5236f23dc6b2b0b701339cd76 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A5rd=20Skaflestad?= <Bard.Skaflestad@sintef.no>
Date: Fri, 4 Sep 2015 15:08:05 +0200
Subject: [PATCH] convertSats(): Transpose loop nest for locality of data

---
 opm/core/simulator/initStateEquil_impl.hpp | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/opm/core/simulator/initStateEquil_impl.hpp b/opm/core/simulator/initStateEquil_impl.hpp
index af25b15a6..a8344a24f 100644
--- a/opm/core/simulator/initStateEquil_impl.hpp
+++ b/opm/core/simulator/initStateEquil_impl.hpp
@@ -780,14 +780,22 @@ namespace Opm
         inline std::vector<double>
         convertSats(const std::vector< std::vector<double> >& sat)
         {
-            const int np = sat.size();
-            const int nc = sat[0].size();
+            const auto np = sat.size();
+            const auto nc = sat[0].size();
+
             std::vector<double> s(np * nc);
-            for (int c = 0; c < nc; ++c) {
-                for (int p = 0; p < np; ++p) {
-                    s[np*c + p] = sat[p][c];
+
+            for (decltype(sat.size()) p = 0; p < np; ++p) {
+                const auto& sat_p = sat[p];
+                double*     sp    = & s[0*nc + p];
+
+                for (decltype(sat[0].size()) c = 0;
+                     c < nc; ++c, sp += np)
+                {
+                    *sp = sat_p[c];
                 }
             }
+
             return s;
         }
     } // namespace Details