Optimize QPager::Compose()

eltociear · Sep 5, 2022 · daf6990 · daf6990
1 parent bafa9c5
commit daf6990
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Showing 2 changed files with 11 additions and 3 deletions.
diff --git a/include/qpager.hpp b/include/qpager.hpp
@@ -25,7 +25,7 @@ typedef std::shared_ptr<QPager> QPagerPtr;
  * A "Qrack::QPager" splits a "Qrack::QEngine" implementation into equal-length "pages." This helps both optimization
  * and distribution of a single coherent quantum register across multiple devices.
  */
-class QPager : public QEngine {
+class QPager : public QEngine, public std::enable_shared_from_this<QEngine> {
 protected:
     bool useHardwareThreshold;
     bool useGpuThreshold;

diff --git a/src/qpager.cpp b/src/qpager.cpp
@@ -564,8 +564,9 @@ void QPager::CombineAndOpControlled(
 
 bitLenInt QPager::Compose(QPagerPtr toCopy)
 {
+    const bitLenInt toRet = qubitCount;
     if (!toCopy->qubitCount) {
-        return qubitCount;
+        return toRet;
     }
 
     const bitLenInt nQubitCount = qubitCount + toCopy->qubitCount;
@@ -580,6 +581,14 @@ bitLenInt QPager::Compose(QPagerPtr toCopy)
         return qPages[0U]->Compose(toCopy->qPages[0U]);
     }
 
+    if (qubitCount < toCopy->qubitCount) {
+        QPagerPtr toCopyClone = std::dynamic_pointer_cast<QPager>(toCopy->Clone());
+        toCopyClone->Compose(shared_from_this(), 0U);
+        qPages = toCopyClone->qPages;
+        SetQubitCount(qubitCount + toCopy->qubitCount);
+        return toRet;
+    }
+
     const bitCapIntOcl nPagePow = pow2Ocl(thresholdQubitsPerPage);
     const bitCapIntOcl pagePow = pageMaxQPower();
     bitCapIntOcl nOffset = 0U;
@@ -618,7 +627,6 @@ bitLenInt QPager::Compose(QPagerPtr toCopy)
     nQPages.pop_back();
     qPages = nQPages;
 
-    bitLenInt toRet = qubitCount;
     SetQubitCount(nQubitCount);
 
     return toRet;