From 0ea3c8088b33a69ffac841661042ddc181634f15 Mon Sep 17 00:00:00 2001
From: WrathfulSpatula <stranoj@gmail.com>
Date: Fri, 31 May 2024 17:27:21 -0400
Subject: [PATCH] Revert "Decompose QFT"

This reverts commit de6f5e085eae8ac71b16622017fdb9f3fa17e568.
---
 pennylane_qrack/QrackDeviceConfig.toml |  2 +-
 pennylane_qrack/qrack_device.cpp       | 14 ++++++++++++++
 pennylane_qrack/qrack_device.py        |  9 +++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/pennylane_qrack/QrackDeviceConfig.toml b/pennylane_qrack/QrackDeviceConfig.toml
index ca3a67e..24ec83d 100644
--- a/pennylane_qrack/QrackDeviceConfig.toml
+++ b/pennylane_qrack/QrackDeviceConfig.toml
@@ -48,6 +48,7 @@ U2 = { properties = [ "controllable", "invertible" ] }
 U1 = { properties = [ "controllable", "invertible" ] }
 MultiControlledX = { properties = [ "controllable", "invertible" ] }
 Identity = { properties = [ "controllable", "invertible" ] }
+QFT = { properties = [ "invertible" ] }
 
 # Operators that should be decomposed according to the algorithm used
 # by PennyLane's device API.
@@ -78,7 +79,6 @@ Identity = { properties = [ "controllable", "invertible" ] }
 # IsingYY = {}
 # IsingZZ = {}
 # IsingXY = {}
-# QFT = {}
 
 # Gates which should be translated to QubitUnitary
 # [operators.gates.matrix]
diff --git a/pennylane_qrack/qrack_device.cpp b/pennylane_qrack/qrack_device.cpp
index 66f3a99..bbfe850 100644
--- a/pennylane_qrack/qrack_device.cpp
+++ b/pennylane_qrack/qrack_device.cpp
@@ -192,6 +192,20 @@ struct QrackDevice final : public Catalyst::Runtime::QuantumDevice {
                     qsim->U(target, Qrack::PI_R1 / 2, params[0U], params[1U]);
                 }
             }
+        } else if (name == "QFT") {
+            const size_t maxLcv = wires.size() >> 1U;
+            const size_t end = wires.size() - 1U;
+            if (inverse) {
+                for (size_t i = 0U; i < maxLcv; ++i) {
+                    qsim->Swap(wires[i], wires[end - i]);
+                }
+                qsim->IQFTR(wires);
+            } else {
+                qsim->QFTR(wires);
+                for (size_t i = 0U; i < maxLcv; ++i) {
+                    qsim->Swap(wires[i], wires[end - i]);
+                }
+            }
         } else if (name != "Identity") {
             throw std::domain_error("Unrecognized gate name: " + name);
         }
diff --git a/pennylane_qrack/qrack_device.py b/pennylane_qrack/qrack_device.py
index 035718e..d7295f7 100644
--- a/pennylane_qrack/qrack_device.py
+++ b/pennylane_qrack/qrack_device.py
@@ -154,6 +154,7 @@ class QrackDevice(QubitDevice):
         "C(CPhase)",
         "MultiControlledX",
         "C(MultiControlledX)",
+        "QFT",
     }
 
     config = pathlib.Path(
@@ -597,6 +598,14 @@ def _apply_gate(self, op):
                 -par[1],
                 -par[2],
             )
+        elif opname == "QFT":
+            self._state.qft(device_wires.labels)
+            for i in range(len(device_wires.labels) >> 1):
+                self._state.swap(device_wires.labels[i], device_wires.labels[-i])
+        elif opname == "QFT.inv":
+            for i in range(len(device_wires.labels) >> 1):
+                self._state.swap(device_wires.labels[i], device_wires.labels[-i])
+            self._state.iqft(device_wires.labels)
         elif opname not in [
             "Identity",
             "Identity.inv",