From 6dffdca123418a1e504c0b9ef5b313c122af246e Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Thu, 7 May 2009 13:13:42 +0000
Subject: [PATCH] fix realloc when initial size was 0 (bug reported by Jens
 Mueller)

---
 Eigen/src/Sparse/SparseMatrix.h | 54 +++++++++++++++++++--------------
 1 file changed, 31 insertions(+), 23 deletions(-)

diff --git a/Eigen/src/Sparse/SparseMatrix.h b/Eigen/src/Sparse/SparseMatrix.h
index c4e2bfc37..8bcf3c8b9 100644
--- a/Eigen/src/Sparse/SparseMatrix.h
+++ b/Eigen/src/Sparse/SparseMatrix.h
@@ -138,7 +138,7 @@ class SparseMatrix
       setZero();
       m_data.reserve(reserveSize);
     }
-    
+
     /** Preallocates \a reserveSize non zeros */
     inline void reserve(int reserveSize)
     {
@@ -175,9 +175,9 @@ class SparseMatrix
       m_data.append(0, inner);
       return m_data.value(id);
     }
-    
+
     //--- low level purely coherent filling ---
-    
+
     inline Scalar& insertBack(int outer, int inner)
     {
       ei_assert(size_t(m_outerIndex[outer+1]) == m_data.size() && "wrong sorted insertion");
@@ -187,14 +187,14 @@ class SparseMatrix
       m_data.append(0, inner);
       return m_data.value(id);
     }
-    
+
     inline void startVec(int outer)
     {
       ei_assert(m_outerIndex[outer]==int(m_data.size()) && "you must call startVec on each inner vec");
       ei_assert(m_outerIndex[outer+1]==0 && "you must call startVec on each inner vec");
       m_outerIndex[outer+1] = m_outerIndex[outer];
     }
-    
+
     //---
 
     /** \deprecated use insert()
@@ -204,20 +204,20 @@ class SparseMatrix
     {
       return insert(row,col);
     }
-    
+
     /** \returns a reference to a novel non zero coefficient with coordinates \a row x \a col.
       * The non zero coefficient must \b not already exist.
-      * 
+      *
       * \warning This function can be extremely slow if the non zero coefficients
       * are not inserted in a coherent order.
-      * 
+      *
       * After an insertion session, you should call the finalize() function.
       */
     EIGEN_DONT_INLINE Scalar& insert(int row, int col)
     {
       const int outer = IsRowMajor ? row : col;
       const int inner = IsRowMajor ? col : row;
-      
+
       int previousOuter = outer;
       if (m_outerIndex[outer+1]==0)
       {
@@ -229,13 +229,13 @@ class SparseMatrix
         }
         m_outerIndex[outer+1] = m_outerIndex[outer];
       }
-      
-      // here we have to handle the tricky case where the outerIndex array 
+
+      // here we have to handle the tricky case where the outerIndex array
       // starts with: [ 0 0 0 0 0 1 ...] and we are inserting in, e.g.,
       // the 2nd inner vector...
       bool isLastVec = (!(previousOuter==-1 && m_data.size()!=0))
                     && (size_t(m_outerIndex[outer+1]) == m_data.size());
-      
+
       size_t startId = m_outerIndex[outer];
       // FIXME let's make sure sizeof(long int) == sizeof(size_t)
       size_t id = m_outerIndex[outer+1];
@@ -244,18 +244,26 @@ class SparseMatrix
       float reallocRatio = 1;
       if (m_data.allocatedSize()<=m_data.size())
       {
-        // we need to reallocate the data, to reduce multiple reallocations
-        // we use a smart resize algorithm based on the current filling ratio
-        // in addition, we use float to avoid integers overflows
-        float nnzEstimate = float(m_outerIndex[outer])*float(m_outerSize)/float(outer+1);
-        reallocRatio = (nnzEstimate-float(m_data.size()))/float(m_data.size());
-        // furthermore we bound the realloc ratio to:
-        //   1) reduce multiple minor realloc when the matrix is almost filled
-        //   2) avoid to allocate too much memory when the matrix is almost empty
-        reallocRatio = std::min(std::max(reallocRatio,1.5f),8.f);
+        // if there is no preallocated memory, let's reserve a minimum of 32 elements
+        if (m_data.size()==0)
+        {
+          m_data.reserve(32);
+        }
+        else
+        {
+          // we need to reallocate the data, to reduce multiple reallocations
+          // we use a smart resize algorithm based on the current filling ratio
+          // in addition, we use float to avoid integers overflows
+          float nnzEstimate = float(m_outerIndex[outer])*float(m_outerSize)/float(outer+1);
+          reallocRatio = (nnzEstimate-float(m_data.size()))/float(m_data.size());
+          // furthermore we bound the realloc ratio to:
+          //   1) reduce multiple minor realloc when the matrix is almost filled
+          //   2) avoid to allocate too much memory when the matrix is almost empty
+          reallocRatio = std::min(std::max(reallocRatio,1.5f),8.f);
+        }
       }
       m_data.resize(m_data.size()+1,reallocRatio);
-      
+
       if (!isLastVec)
       {
         if (previousOuter==-1)
@@ -310,7 +318,7 @@ class SparseMatrix
     }
 
     EIGEN_DEPRECATED void endFill() { finalize(); }
-    
+
     /** Must be called after inserting a set of non zero entries.
       */
     inline void finalize()