Reverse QPager::Compose() (debugged)

unitaryfund · Jul 10, 2021 · 3e033bd · 3e033bd
1 parent 1c6be43
commit 3e033bd
Showing 1 changed file with 40 additions and 1 deletion.
diff --git a/src/qpager.cpp b/src/qpager.cpp
@@ -438,7 +438,46 @@ void QPager::CombineAndOpControlled(
     CombineAndOp(fn, bits);
 }
 
-bitLenInt QPager::Compose(QPagerPtr toCopy) { return Compose(toCopy, qubitCount); }
+bitLenInt QPager::Compose(QPagerPtr toCopy)
+{
+    if (qubitCount >= toCopy->qubitCount) {
+        return Compose(toCopy, qubitCount);
+    }
+
+    if ((qubitCount + toCopy->qubitCount) > maxQubits) {
+        throw std::invalid_argument(
+            "Cannot instantiate a QPager with greater capacity than environment variable QRACK_MAX_PAGING_QB.");
+    }
+
+    // TODO: Avoid CombineEngines();
+    toCopy->CombineEngines();
+
+    bitLenInt qpp = qubitsPerPage();
+    bitLenInt tcqpp = toCopy->qubitCount;
+
+    if ((qpp + tcqpp) > maxPageQubits) {
+        qpp = (maxPageQubits <= tcqpp) ? 1U : (maxPageQubits - tcqpp);
+        SeparateEngines(qpp, true);
+    }
+
+    bitCapIntOcl i;
+    bitCapIntOcl maxI = (bitCapIntOcl)qPages.size();
+    std::vector<QEnginePtr> nQPages;
+
+    QEnginePtr engine = toCopy->qPages[0];
+    for (i = 0; i < maxI; i++) {
+        nQPages.push_back(std::dynamic_pointer_cast<QEngine>(engine->Clone()));
+        nQPages.back()->Compose(qPages[i], 0);
+    }
+
+    qPages = nQPages;
+
+    bitLenInt toRet = qubitCount;
+
+    SetQubitCount(qubitCount + toCopy->qubitCount);
+
+    return toRet;
+}
 
 bitLenInt QPager::Compose(QPagerPtr toCopy, bitLenInt start)
 {