[WIP] Use native bits and registers for CircuitData.

crates/circuit/src/bit.rs

@@ -0,0 +1,77 @@
+// This code is part of Qiskit.
+//
+// (C) Copyright IBM 2025
+//
+// This code is licensed under the Apache License, Version 2.0. You may
+// obtain a copy of this license in the LICENSE.txt file in the root directory
+// of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+//
+// Any modifications or derivative works of this code must retain this
+// copyright notice, and modified files need to carry a notice indicating
+// that they have been altered from the originals.
+
+use std::fmt::Debug;
+
+/// Keeps information about where a bit is located within the circuit.
+///
+/// This information includes whether the bit was added by a register,
+/// which register it belongs to and where it is located within it.
+#[derive(Debug, Clone, PartialEq, PartialOrd, Ord, Eq, Hash)]
+pub struct BitInfo {
+    added_by_reg: bool,
+    registers: Vec<BitLocation>,
+}
+
+impl BitInfo {
+    pub fn new(orig_reg: Option<(u32, u32)>) -> Self {
+        // If the instance was added by a register, add it and prefil its locator
+        if let Some((reg_idx, idx)) = orig_reg {
+            Self {
+                added_by_reg: true,
+                registers: vec![BitLocation::new(reg_idx, idx)],
+            }
+        } else {
+            Self {
+                added_by_reg: false,
+                registers: vec![],
+            }
+        }
+    }
+
+    /// Add a register to the bit instance
+    pub fn add_register(&mut self, register: u32, index: u32) {
+        self.registers.push(BitLocation(register, index))
+    }
+
+    /// Returns a list with all the [BitLocation] instances
+    pub fn get_registers(&self) -> &[BitLocation] {
+        &self.registers
+    }
+
+    /// Returns the index of the original register if any exists
+    pub fn orig_register_index(&self) -> Option<&BitLocation> {
+        if self.added_by_reg {
+            Some(&self.registers[0])
+        } else {
+            None
+        }
+    }
+}
+
+/// Keeps information about where a qubit is located within a register.
+#[derive(Debug, Clone, Copy, PartialEq, PartialOrd, Ord, Eq, Hash)]
+pub struct BitLocation(u32, u32);
+
+impl BitLocation {
+    pub fn new(register_idx: u32, index: u32) -> Self {
+        Self(register_idx, index)
+    }
+
+    pub fn register_index(&self) -> u32 {
+        self.0
+    }
+
+    pub fn index(&self) -> u32 {
+        self.1
+    }
+}