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//! Metal-based GPU acceleration for macOS
//!
//! This module provides GPU acceleration using Apple's Metal API
//! for quantum circuit simulation on macOS devices.
//!
//! **Status:** scaffolding only — the Metal compute backend is not yet
//! implemented. All entry points honestly return errors or report unavailability
//! (via SciRS2 platform detection) rather than fabricating results. A future
//! implementation would use Metal Performance Shaders (MPS) and Metal Compute
//! Shaders, covering:
//! - State vector allocation using Metal buffers
//! - Quantum gate kernels using Metal shaders
//! - Memory management for unified memory architecture
//! - Optimizations for Apple Silicon (M1/M2/M3)
use crate::error::{Result, SimulatorError};
use quantrs2_circuit::prelude::Circuit;
use quantrs2_core::prelude::QubitId;
use std::sync::Arc;
/// Metal-based GPU simulator for macOS
pub struct MetalGpuSimulator {
/// Number of qubits
num_qubits: usize,
/// Metal device handle (placeholder)
_device: Arc<()>,
}
impl MetalGpuSimulator {
/// Create a new Metal GPU simulator.
///
/// The Metal compute backend is not yet implemented, so this honestly returns
/// an error rather than fabricating a non-functional simulator. The error text
/// reflects whether a Metal-capable platform was actually detected.
pub fn new(num_qubits: usize) -> Result<Self> {
let _ = num_qubits;
if Self::is_available() {
Err(SimulatorError::GpuError(
"Metal-capable platform detected, but the QuantRS2 Metal backend is not yet \
implemented. Please use CPU simulation on macOS for now."
.to_string(),
))
} else {
Err(SimulatorError::GpuError(
"Metal GPU is not available on this platform. Please use CPU simulation."
.to_string(),
))
}
}
/// Simulate a quantum circuit
pub fn simulate<const N: usize>(&mut self, _circuit: &Circuit<N>) -> Result<()> {
Err(SimulatorError::GpuError(
"Metal GPU simulation not yet implemented".to_string(),
))
}
/// Get available Metal devices.
///
/// No Metal backend is implemented yet, so no Metal devices are enumerated
/// even on macOS — reported honestly rather than fabricating device names.
pub fn available_devices() -> Vec<String> {
Vec::new()
}
/// Check if Metal acceleration is available on this system.
///
/// Delegates to SciRS2's platform detection (`metal_available`), which is true
/// only on macOS with the Metal backend compiled in. The QuantRS2 Metal
/// *compute* path is still unimplemented, so [`Self::new`] refuses even when
/// this returns `true` — it never fabricates results.
pub fn is_available() -> bool {
scirs2_core::simd_ops::PlatformCapabilities::detect().metal_available
}
}
/// Metal GPU backend interface (placeholder for future implementation)
pub trait MetalBackend {
/// Allocate state vector on GPU
fn allocate_state_vector(&self, size: usize) -> Result<()>;
/// Apply quantum gate
fn apply_gate(&self, gate: &str, qubits: &[QubitId]) -> Result<()>;
/// Transfer data between CPU and GPU
fn sync(&self) -> Result<()>;
}