Debug QUnit::TryDecompose()

unitaryfund · Nov 6, 2024 · 610b9cf · 610b9cf
1 parent 8457950
commit 610b9cf
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Showing 2 changed files with 21 additions and 28 deletions.
diff --git a/include/qunit.hpp b/include/qunit.hpp
@@ -120,11 +120,16 @@ class QUnit : public QParity, public QInterface {
 
         const bitLenInt length = dest->GetQubitCount();
 
+        if ((start + length) > qubitCount) {
+            throw std::invalid_argument("QUnit::TryDecompose qubit range out-of-bounds!");
+        }
+
         for (bitLenInt i = 0U; i < length; ++i) {
-            if (!shards[i].unit) {
+            QEngineShard& shard = shards[start + i];
+            if (!shard.unit) {
                 continue;
             }
-            if (!shards[i].unit->isBinaryDecisionTree()) {
+            if (!shard.unit->isBinaryDecisionTree()) {
                 return QInterface::TryDecompose(start, dest, error_tol);
             }
         }
@@ -135,17 +140,18 @@ class QUnit : public QParity, public QInterface {
             Swap(start + i, qubitCount - (i + 1U));
         }
 
-        const bool isSeparable = TryDetach(nStart);
+        if (TryDetach(nStart)) {
+            Decompose(qubitCount - length, dest);
+            for (bitLenInt i = shift; i > 0U; --i) {
+                dest->Swap(i - 1U, dest->GetQubitCount() - i);
+            }
+            return true;
+        }
 
         for (bitLenInt i = shift; i > 0U; --i) {
             Swap(start + (i - 1U), qubitCount - i);
         }
 
-        if (isSeparable) {
-            Decompose(start, dest);
-            return true;
-        }
-
         return false;
     }
 

diff --git a/src/qunit.cpp b/src/qunit.cpp
@@ -386,7 +386,10 @@ void QUnit::Detach(bitLenInt start, bitLenInt length, QUnitPtr dest)
 
 bool QUnit::TryDetach(bitLenInt length)
 {
-    if (!length || (length > qubitCount)) {
+    if (!length || (length == qubitCount)) {
+        return true;
+    }
+    if (length > qubitCount) {
         throw std::invalid_argument("QUnit::Detach range is out-of-bounds!");
     }
 
@@ -417,26 +420,10 @@ bool QUnit::TryDetach(bitLenInt length)
     // After ordering all subunits contiguously, since the top level mapping is a contiguous array, all subunit sets are
     // also contiguous. From the lowest index bits, they are mapped simply for the length count of bits involved in the
     // entire subunit.
-    std::map<QBdtPtr, bitLenInt> decomposedUnits;
-    for (bitLenInt i = 0U; i < length; ++i) {
-        QEngineShard& shard = shards[start + i];
-        QBdtPtr unit = std::dynamic_pointer_cast<QBdt>(shard.unit);
-
-        if (unit == NULL) {
-            continue;
-        }
-
-        if (decomposedUnits.find(unit) == decomposedUnits.end()) {
-            decomposedUnits[unit] = start + i;
-            const bitLenInt subLen = subunits[unit];
-            const bitLenInt origLen = unit->GetQubitCount();
-            if ((subLen != origLen) && !unit->IsSeparable(shard.mapped)) {
-                return false;
-            }
-        }
-    }
+    QEngineShard& shard = shards[start];
+    QBdtPtr unit = std::dynamic_pointer_cast<QBdt>(shard.unit);
 
-    return true;
+    return (unit == NULL) || (shard.mapped == 0U) || unit->IsSeparable(shard.mapped);
 }
 
 QInterfacePtr QUnit::EntangleInCurrentBasis(