From eede526b7c4be526deca424ba9d3ac729098a3e7 Mon Sep 17 00:00:00 2001
From: Andreas Forster <an.forster@gmail.com>
Date: Mon, 22 Jan 2024 00:35:31 +0000
Subject: [PATCH] [Compressed Storage] Use smaller type of Index & StorageIndex
 for determining maximum size during resize.

---
 Eigen/src/SparseCore/CompressedStorage.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Eigen/src/SparseCore/CompressedStorage.h b/Eigen/src/SparseCore/CompressedStorage.h
index 123c89c0d..8f8a6963a 100644
--- a/Eigen/src/SparseCore/CompressedStorage.h
+++ b/Eigen/src/SparseCore/CompressedStorage.h
@@ -71,8 +71,13 @@ class CompressedStorage {
 
   void resize(Index size, double reserveSizeFactor = 0) {
     if (m_allocatedSize < size) {
+      // Avoid underflow on the std::min<Index> call by choosing the smaller index type.
+      using SmallerIndexType =
+          typename std::conditional<static_cast<size_t>((std::numeric_limits<Index>::max)()) <
+                                        static_cast<size_t>((std::numeric_limits<StorageIndex>::max)()),
+                                    Index, StorageIndex>::type;
       Index realloc_size =
-          (std::min<Index>)(NumTraits<StorageIndex>::highest(), size + Index(reserveSizeFactor * double(size)));
+          (std::min<Index>)(NumTraits<SmallerIndexType>::highest(), size + Index(reserveSizeFactor * double(size)));
       if (realloc_size < size) internal::throw_std_bad_alloc();
       reallocate(realloc_size);
     }