From a0a6dfb19dce0a848474c9b3fd6dd50ff2df039a Mon Sep 17 00:00:00 2001
From: graham <g.macpherson@opencfd.co.uk>
Date: Wed, 22 Jun 2011 17:33:04 +0100
Subject: [PATCH] ENH: Prevent overflow in weight field.

---
 .../decompose/ptscotchDecomp/ptscotchDecomp.C | 33 +++++++++++++++++--
 .../decompose/scotchDecomp/scotchDecomp.C     | 14 +++-----
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/src/parallel/decompose/ptscotchDecomp/ptscotchDecomp.C b/src/parallel/decompose/ptscotchDecomp/ptscotchDecomp.C
index 655b58fde1..833cb5d461 100644
--- a/src/parallel/decompose/ptscotchDecomp/ptscotchDecomp.C
+++ b/src/parallel/decompose/ptscotchDecomp/ptscotchDecomp.C
@@ -483,8 +483,10 @@ if (debug)
 
 
     // Check for externally provided cellweights and if so initialise weights
+
     scalar minWeights = gMin(cWeights);
-    if (cWeights.size() > 0)
+
+    if (!cWeights.empty())
     {
         if (minWeights <= 0)
         {
@@ -504,12 +506,39 @@ if (debug)
                 << " does not equal number of cells " << xadj.size()-1
                 << exit(FatalError);
         }
+    }
 
+    scalar velotabSum = gSum(cWeights)/minWeights;
+
+    scalar rangeScale(1.0);
+
+    if (Pstream::master())
+    {
+        if (velotabSum > scalar(INT_MAX - 1))
+        {
+            // 0.9 factor of safety to avoid floating point round-off in
+            // rangeScale tipping the subsequent sum over the integer limit.
+            rangeScale = 0.9*scalar(INT_MAX - 1)/velotabSum;
+
+            WarningIn
+            (
+                "ptscotchDecomp::decompose(...)"
+            )   << "Sum of weights has overflowed integer: " << velotabSum
+                << ", compressing weight scale by a factor of " << rangeScale
+                << endl;
+        }
+    }
+
+    Pstream::scatter(rangeScale);
+
+    if (!cWeights.empty())
+    {
         // Convert to integers.
         velotab.setSize(cWeights.size());
+
         forAll(velotab, i)
         {
-            velotab[i] = int(cWeights[i]/minWeights);
+            velotab[i] = int((cWeights[i]/minWeights - 1)*rangeScale) + 1;
         }
     }
 
diff --git a/src/parallel/decompose/scotchDecomp/scotchDecomp.C b/src/parallel/decompose/scotchDecomp/scotchDecomp.C
index 0851431b96..dfc6e1c421 100644
--- a/src/parallel/decompose/scotchDecomp/scotchDecomp.C
+++ b/src/parallel/decompose/scotchDecomp/scotchDecomp.C
@@ -386,14 +386,13 @@ Foam::label Foam::scotchDecomp::decomposeOneProc
     // Check for externally provided cellweights and if so initialise weights
     // Note: min, not gMin since routine runs on master only.
     scalar minWeights = min(cWeights);
-    if (cWeights.size() > 0)
+    if (!cWeights.empty())
     {
         if (minWeights <= 0)
         {
             WarningIn
             (
-                "scotchDecomp::decompose"
-                "(const pointField&, const scalarField&)"
+                "scotchDecomp::decompose(...)"
             )   << "Illegal minimum weight " << minWeights
                 << endl;
         }
@@ -402,8 +401,7 @@ Foam::label Foam::scotchDecomp::decomposeOneProc
         {
             FatalErrorIn
             (
-                "scotchDecomp::decompose"
-                "(const pointField&, const scalarField&)"
+                "scotchDecomp::decompose(...)"
             )   << "Number of cell weights " << cWeights.size()
                 << " does not equal number of cells " << xadj.size()-1
                 << exit(FatalError);
@@ -421,8 +419,7 @@ Foam::label Foam::scotchDecomp::decomposeOneProc
 
             WarningIn
             (
-                "scotchDecomp::decompose"
-                "(const pointField&, const scalarField&)"
+                "scotchDecomp::decompose(...)"
             )   << "Sum of weights has overflowed integer: " << velotabSum
                 << ", compressing weight scale by a factor of " << rangeScale
                 << endl;
@@ -433,8 +430,7 @@ Foam::label Foam::scotchDecomp::decomposeOneProc
 
         forAll(velotab, i)
         {
-            velotab[i] =
-                int((cWeights[i]/minWeights - 1)*rangeScale) + 1;
+            velotab[i] = int((cWeights[i]/minWeights - 1)*rangeScale) + 1;
         }
     }