Optimize LM controlled kernels [sc-73461]

.github/CHANGELOG.md

@@ -45,6 +45,9 @@
 * Update GitHub actions in response to a high-severity vulnerability.
   [(#887)](https://github.com/PennyLaneAI/pennylane-lightning/pull/887)
 
+* Optimize and simplify controlled kernels in Lightning-Qubit.
+  [(#882)](https://github.com/PennyLaneAI/pennylane-lightning/pull/882)
+
 * Optimize gate cache recording for `lightning.tensor` C++ layer.
   [(#879)](https://github.com/PennyLaneAI/pennylane-lightning/pull/879)
 

pennylane_lightning/core/_version.py

@@ -16,4 +16,4 @@
    Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.39.0-dev19"
+__version__ = "0.39.0-dev20"

pennylane_lightning/core/src/simulators/lightning_qubit/gates/GateIndices.cpp

@@ -47,4 +47,37 @@ auto generateBitPatterns(const std::vector<std::size_t> &qubitIndices,
     }
     return indices;
 }
+
+/**
+ * @brief Introduce quantum controls in indices generated by
+ * generateBitPatterns.
+ *
+ * @param indices Indices for the operation.
+ * @param num_qubits Number of qubits in register.
+ * @param controlled_wires Control wires.
+ * @param controlled_values Control values (false or true).
+ */
+void controlBitPatterns(std::vector<std::size_t> &indices,
+                        const std::size_t num_qubits,
+                        const std::vector<std::size_t> &controlled_wires,
+                        const std::vector<bool> &controlled_values) {
+    constexpr std::size_t one{1U};
+    if (controlled_wires.empty()) {
+        return;
+    }
+    std::vector<std::size_t> controlled_values_i(controlled_values.size());
+    std::transform(controlled_values.begin(), controlled_values.end(),
+                   controlled_values_i.begin(),
+                   [](const bool v) { return static_cast<std::size_t>(v); });
+    std::for_each(
+        indices.begin(), indices.end(),
+        [num_qubits, &controlled_wires, &controlled_values_i](std::size_t &i) {
+            for (std::size_t k = 0; k < controlled_wires.size(); k++) {
+                const std::size_t rev_wire =
+                    (num_qubits - 1) - controlled_wires[k];
+                const std::size_t value = controlled_values_i[k];
+                i = (i & ~(one << rev_wire)) | (value << rev_wire);
+            }
+        });
+}
 } // namespace Pennylane::LightningQubit::Gates

pennylane_lightning/core/src/simulators/lightning_qubit/gates/GateIndices.hpp

@@ -56,6 +56,19 @@ auto getIndicesAfterExclusion(const std::vector<std::size_t> &indicesToExclude,
 auto generateBitPatterns(const std::vector<std::size_t> &qubitIndices,
                          std::size_t num_qubits) -> std::vector<std::size_t>;
 
+/**
+ * @brief Introduce quantum controls in indices generated by
+ * generateBitPatterns.
+ *
+ * @param indices Indices for the operation.
+ * @param num_qubits Number of qubits in register.
+ * @param controlled_wires Control wires.
+ * @param controlled_values Control values (false or true).
+ */
+void controlBitPatterns(std::vector<std::size_t> &indices,
+                        std::size_t num_qubits,
+                        const std::vector<std::size_t> &controlled_wires,
+                        const std::vector<bool> &controlled_values);
 /**
  * @brief Internal utility struct to track data indices of application for
  * operations.