Allow init with 0 mem size

include/mallocMC/creationPolicies/FlatterScatter.hpp

@@ -411,6 +411,12 @@ namespace mallocMC::CreationPolicies
         {
             using MyHeap = FlatterScatterAlloc::Heap<T_HeapConfig, T_HashConfig, T_AlignmentPolicy>;
             auto numBlocks = MyHeap::numBlocks(memsize);
+            if(numBlocks == 0U)
+            {
+                // This is not just an optimisation. The call to `getValidWorkDiv` below really dislikes the 0 extent
+                // that we'd give it, so better stop here to not run into division by zero.
+                return;
+            }
             auto numPagesPerBlock = MyHeap::MyAccessBlock::numPages();
 
             alpaka::KernelCfg<TAcc> const kernelCfg

test/unit/source/Allocator.cpp

@@ -0,0 +1,62 @@
+/*
+  mallocMC: Memory Allocator for Many Core Architectures.
+
+  Copyright 2025 Helmholtz-Zentrum Dresden - Rossendorf
+
+  Author(s):  Julian Johannes Lenz, Rene Widera
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+  THE SOFTWARE.
+*/
+
+#include "mallocMC/allocator.hpp"
+
+#include "mallocMC/alignmentPolicies/Shrink.hpp"
+#include "mallocMC/creationPolicies/FlatterScatter.hpp"
+#include "mallocMC/distributionPolicies/Noop.hpp"
+#include "mallocMC/oOMPolicies/ReturnNull.hpp"
+#include "mallocMC/reservePoolPolicies/AlpakaBuf.hpp"
+
+#include <alpaka/example/ExampleDefaultAcc.hpp>
+
+#include <catch2/catch_test_macros.hpp>
+#include <mallocMC/mallocMC.hpp>
+using Dim = alpaka::DimInt<1>;
+using Idx = std::size_t;
+
+// Define the device accelerator
+using Acc = alpaka::ExampleDefaultAcc<Dim, Idx>;
+
+TEST_CASE("Allocator")
+{
+    SECTION("can be initialised with 0 memory.")
+    {
+        auto const platform = alpaka::Platform<Acc>{};
+        auto const dev = alpaka::getDevByIdx(platform, 0);
+        auto queue = alpaka::Queue<Acc, alpaka::Blocking>{dev};
+
+        mallocMC::Allocator<
+            Acc,
+            mallocMC::CreationPolicies::FlatterScatter<>,
+            mallocMC::DistributionPolicies::Noop,
+            mallocMC::OOMPolicies::ReturnNull,
+            mallocMC::ReservePoolPolicies::AlpakaBuf<Acc>,
+            mallocMC::AlignmentPolicies::Shrink<>>
+            allocator{dev, queue, 0};
+    }
+}