Move functions to base class (#841)

**Context:** Some of these functions are needed in Catalyst. Since
Catalyst does not use LM, but instead uses LightningDynamic, the least
upper bound in the class hierarchy is `StateVectorLQubit`.

**Description of the Change:** Move these functions to
`StateVetctorLQubit`.

**Benefits:** Code-reuse

**Possible Drawbacks:**

**Related GitHub Issues:**

---------

Co-authored-by: ringo-but-quantum <[email protected]>
Co-authored-by: Vincent Michaud-Rioux <[email protected]>
Co-authored-by: Ali Asadi <[email protected]>

.github/CHANGELOG.md

@@ -67,6 +67,9 @@
 * Add `initial_state_prep` option to Catalyst TOML file.
   [(#826)](https://github.com/PennyLaneAI/pennylane-lightning/pull/826)
 
+* Move `setBasisState`, `setStateVector` and `resetStateVector` from `StateVectorLQubitManaged` to `StateVectorLQubit`.
+  [(#841)](https://github.com/PennyLaneAI/pennylane-lightning/pull/841)
+
 ### Documentation
 
 * Updated the README and added citation format for Lightning arxiv preprint.

pennylane_lightning/core/_version.py

@@ -16,4 +16,4 @@
    Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.38.0-dev26"
+__version__ = "0.38.0-dev27"

pennylane_lightning/core/src/simulators/lightning_qubit/StateVectorLQubit.hpp

@@ -687,5 +687,50 @@ class StateVectorLQubit : public StateVectorBase<PrecisionT, Derived> {
             arr[k] *= inv_norm;
         }
     }
+
+    /**
+     * @brief Prepares a single computational basis state.
+     *
+     * @param index Index of the target element.
+     */
+    void setBasisState(const std::size_t index) {
+        auto length = this->getLength();
+        PL_ABORT_IF(index > length - 1, "Invalid index");
+
+        auto *arr = this->getData();
+        std::fill(arr, arr + length, 0.0);
+        arr[index] = {1.0, 0.0};
+    }
+
+    /**
+     * @brief Set values for a batch of elements of the state-vector.
+     *
+     * @param values Values to be set for the target elements.
+     * @param indices Indices of the target elements.
+     */
+    void setStateVector(const std::vector<std::size_t> &indices,
+                        const std::vector<ComplexT> &values) {
+        auto num_indices = indices.size();
+        PL_ABORT_IF(num_indices != values.size(),
+                    "Indices and values length must match");
+
+        auto *arr = this->getData();
+        auto length = this->getLength();
+        std::fill(arr, arr + length, 0.0);
+        for (std::size_t i = 0; i < num_indices; i++) {
+            PL_ABORT_IF(i >= length, "Invalid index");
+            arr[indices[i]] = values[i];
+        }
+    }
+
+    /**
+     * @brief Reset the data back to the \f$\ket{0}\f$ state.
+     *
+     */
+    void resetStateVector() {
+        if (this->getLength()) {
+            setBasisState(0U);
+        }
+    }
 };
 } // namespace Pennylane::LightningQubit

pennylane_lightning/core/src/simulators/lightning_qubit/StateVectorLQubitManaged.hpp

@@ -140,39 +140,6 @@ class StateVectorLQubitManaged final
 
     ~StateVectorLQubitManaged() = default;
 
-    /**
-     * @brief Prepares a single computational basis state.
-     *
-     * @param index Index of the target element.
-     */
-    void setBasisState(const std::size_t index) {
-        std::fill(data_.begin(), data_.end(), 0.0);
-        data_[index] = {1.0, 0.0};
-    }
-
-    /**
-     * @brief Set values for a batch of elements of the state-vector.
-     *
-     * @param values Values to be set for the target elements.
-     * @param indices Indices of the target elements.
-     */
-    void setStateVector(const std::vector<std::size_t> &indices,
-                        const std::vector<ComplexT> &values) {
-        for (std::size_t n = 0; n < indices.size(); n++) {
-            data_[indices[n]] = values[n];
-        }
-    }
-
-    /**
-     * @brief Reset the data back to the \f$\ket{0}\f$ state.
-     *
-     */
-    void resetStateVector() {
-        if (this->getLength() > 0) {
-            setBasisState(0U);
-        }
-    }
-
     [[nodiscard]] auto getData() -> ComplexT * { return data_.data(); }
 
     [[nodiscard]] auto getData() const -> const ComplexT * {
@@ -218,4 +185,4 @@ class StateVectorLQubitManaged final
         return data_.get_allocator();
     }
 };
-} // namespace Pennylane::LightningQubit
+} // namespace Pennylane::LightningQubit