quantrs2_tytan/sampler/hardware/

fpga.rs

//! Quantum-inspired FPGA accelerator integration
//!
//! This module provides integration with FPGA-based quantum-inspired
//! optimization accelerators.

#![allow(dead_code)]

use crate::sampler::{SampleResult, Sampler, SamplerError, SamplerResult};
use scirs2_core::ndarray::Array2;
use std::cell::RefCell;
use std::collections::HashMap;

/// FPGA accelerator configuration
#[derive(Debug, Clone)]
pub struct FPGAConfig {
    /// Device identifier
    pub device_id: String,
    /// FPGA platform
    pub platform: FPGAPlatform,
    /// Clock frequency (MHz)
    pub clock_frequency: u32,
    /// Parallelism level
    pub parallelism: ParallelismConfig,
    /// Memory configuration
    pub memory_config: MemoryConfig,
    /// Optimization algorithm
    pub algorithm: FPGAAlgorithm,
}

#[derive(Debug, Clone)]
pub enum FPGAPlatform {
    /// Xilinx Alveo series
    XilinxAlveo { model: String },
    /// Intel Stratix series
    IntelStratix { model: String },
    /// AWS F1 instances
    AWSF1 { instance_type: String },
    /// Custom FPGA board
    Custom {
        vendor: String,
        model: String,
        resources: FPGAResources,
    },
}

#[derive(Debug, Clone)]
pub struct FPGAResources {
    /// Number of logic elements
    pub logic_elements: u32,
    /// Number of DSP blocks
    pub dsp_blocks: u32,
    /// On-chip memory (MB)
    pub on_chip_memory: u32,
    /// External memory bandwidth (GB/s)
    pub memory_bandwidth: f32,
}

#[derive(Debug, Clone)]
pub struct ParallelismConfig {
    /// Number of parallel spin updaters
    pub spin_updaters: u32,
    /// Pipeline depth
    pub pipeline_depth: u32,
    /// Batch size for parallel processing
    pub batch_size: u32,
    /// Enable dynamic parallelism
    pub dynamic_parallelism: bool,
}

#[derive(Debug, Clone)]
pub struct MemoryConfig {
    /// Use HBM (High Bandwidth Memory)
    pub use_hbm: bool,
    /// DDR channels
    pub ddr_channels: u32,
    /// Cache configuration
    pub cache_config: CacheConfig,
}

#[derive(Debug, Clone)]
pub struct CacheConfig {
    /// L1 cache size per processing element (KB)
    pub l1_size: u32,
    /// L2 cache size (MB)
    pub l2_size: u32,
    /// Cache line size (bytes)
    pub line_size: u32,
}

#[derive(Debug, Clone)]
pub enum FPGAAlgorithm {
    /// Simulated Bifurcation Machine
    SimulatedBifurcation {
        time_step: f64,
        damping: f64,
        pressure: f64,
    },
    /// Digital Annealing
    DigitalAnnealing {
        flip_strategy: FlipStrategy,
        temperature_schedule: String,
    },
    /// Momentum Annealing
    MomentumAnnealing { momentum: f64, learning_rate: f64 },
    /// Parallel Tempering
    ParallelTempering {
        num_replicas: u32,
        temperature_range: (f64, f64),
    },
    /// Custom algorithm
    Custom {
        name: String,
        parameters: HashMap<String, f64>,
    },
}

#[derive(Debug, Clone)]
pub enum FlipStrategy {
    /// Single spin flip
    SingleFlip,
    /// Multi-spin flip
    MultiFlip { max_flips: u32 },
    /// Cluster flip
    ClusterFlip,
    /// Adaptive flip
    AdaptiveFlip,
}

impl Default for FPGAConfig {
    fn default() -> Self {
        Self {
            device_id: "fpga0".to_string(),
            platform: FPGAPlatform::XilinxAlveo {
                model: "U280".to_string(),
            },
            clock_frequency: 300,
            parallelism: ParallelismConfig {
                spin_updaters: 64,
                pipeline_depth: 16,
                batch_size: 1024,
                dynamic_parallelism: true,
            },
            memory_config: MemoryConfig {
                use_hbm: true,
                ddr_channels: 4,
                cache_config: CacheConfig {
                    l1_size: 32,
                    l2_size: 16,
                    line_size: 64,
                },
            },
            algorithm: FPGAAlgorithm::SimulatedBifurcation {
                time_step: 0.1,
                damping: 0.3,
                pressure: 0.01,
            },
        }
    }
}

/// FPGA-accelerated sampler
pub struct FPGASampler {
    config: FPGAConfig,
    /// Device handle
    device: RefCell<Option<FPGADevice>>,
    /// Problem size limit
    max_problem_size: usize,
    /// Performance monitor
    perf_monitor: RefCell<PerformanceMonitor>,
}

/// FPGA device abstraction
#[derive(Debug)]
struct FPGADevice {
    device_id: String,
    is_initialized: bool,
    current_bitstream: Option<String>,
}

/// Performance monitoring
#[derive(Debug, Clone)]
struct PerformanceMonitor {
    /// Track kernel execution times
    kernel_times: Vec<f64>,
    /// Track data transfer times
    transfer_times: Vec<f64>,
    /// Track energy consumption
    energy_consumption: Vec<f64>,
}

impl FPGASampler {
    /// Create new FPGA sampler
    pub fn new(config: FPGAConfig) -> Self {
        let max_problem_size = match &config.platform {
            FPGAPlatform::XilinxAlveo { model } => match model.as_str() {
                "U280" => 8192,
                "U250" => 4096,
                _ => 2048,
            },
            FPGAPlatform::IntelStratix { .. } => 4096,
            FPGAPlatform::AWSF1 { .. } => 8192,
            FPGAPlatform::Custom { resources, .. } => (resources.logic_elements / 100) as usize,
        };

        Self {
            config,
            device: RefCell::new(None),
            max_problem_size,
            perf_monitor: RefCell::new(PerformanceMonitor {
                kernel_times: Vec::new(),
                transfer_times: Vec::new(),
                energy_consumption: Vec::new(),
            }),
        }
    }

    /// Initialize FPGA device
    fn initialize_device(&self) -> Result<(), SamplerError> {
        if self.device.borrow().is_some() {
            return Ok(());
        }

        // Load appropriate bitstream based on algorithm
        let bitstream = self.select_bitstream()?;

        *self.device.borrow_mut() = Some(FPGADevice {
            device_id: self.config.device_id.clone(),
            is_initialized: true,
            current_bitstream: Some(bitstream),
        });

        Ok(())
    }

    /// Select bitstream based on algorithm and problem size
    fn select_bitstream(&self) -> Result<String, SamplerError> {
        match &self.config.algorithm {
            FPGAAlgorithm::SimulatedBifurcation { .. } => Ok("sbm_optimizer_v2.bit".to_string()),
            FPGAAlgorithm::DigitalAnnealing { .. } => Ok("digital_annealing_v3.bit".to_string()),
            FPGAAlgorithm::MomentumAnnealing { .. } => Ok("momentum_annealing_v1.bit".to_string()),
            FPGAAlgorithm::ParallelTempering { .. } => Ok("parallel_tempering_v2.bit".to_string()),
            FPGAAlgorithm::Custom { name, .. } => Ok(format!("{name}_custom.bit")),
        }
    }

    /// Execute on FPGA
    fn execute_on_fpga(
        &self,
        qubo: &Array2<f64>,
        shots: usize,
    ) -> Result<Vec<FPGAResult>, SamplerError> {
        self.initialize_device()?;

        // Transfer data to FPGA
        let transfer_start = std::time::Instant::now();
        self.transfer_problem_to_device(qubo)?;
        self.perf_monitor
            .borrow_mut()
            .transfer_times
            .push(transfer_start.elapsed().as_secs_f64());

        // Execute kernel
        let kernel_start = std::time::Instant::now();
        let results = match &self.config.algorithm {
            FPGAAlgorithm::SimulatedBifurcation {
                time_step,
                damping,
                pressure,
            } => self.run_sbm_kernel(qubo, shots, *time_step, *damping, *pressure)?,
            FPGAAlgorithm::DigitalAnnealing { .. } => {
                self.run_digital_annealing_kernel(qubo, shots)?
            }
            _ => {
                return Err(SamplerError::UnsupportedOperation(
                    "Algorithm not yet implemented for FPGA".to_string(),
                ));
            }
        };
        self.perf_monitor
            .borrow_mut()
            .kernel_times
            .push(kernel_start.elapsed().as_secs_f64());

        Ok(results)
    }

    /// Transfer problem to device memory
    const fn transfer_problem_to_device(&self, _qubo: &Array2<f64>) -> Result<(), SamplerError> {
        // In real implementation:
        // 1. Convert QUBO to fixed-point representation
        // 2. Transfer to HBM/DDR
        // 3. Set up DMA transfers
        Ok(())
    }

    /// Run Simulated Bifurcation Machine kernel
    fn run_sbm_kernel(
        &self,
        qubo: &Array2<f64>,
        _shots: usize,
        _time_step: f64,
        _damping: f64,
        _pressure: f64,
    ) -> Result<Vec<FPGAResult>, SamplerError> {
        // Placeholder implementation
        let n = qubo.shape()[0];
        Ok(vec![FPGAResult {
            spins: vec![1; n],
            positions: vec![0.5; n],
            momenta: vec![0.0; n],
            energy: -100.0,
            iterations: 1000,
        }])
    }

    /// Run Digital Annealing kernel
    fn run_digital_annealing_kernel(
        &self,
        qubo: &Array2<f64>,
        _shots: usize,
    ) -> Result<Vec<FPGAResult>, SamplerError> {
        // Placeholder implementation
        let n = qubo.shape()[0];
        Ok(vec![FPGAResult {
            spins: vec![-1; n],
            positions: vec![0.0; n],
            momenta: vec![0.0; n],
            energy: -80.0,
            iterations: 5000,
        }])
    }

    /// Convert FPGA result to sample result
    fn convert_result(
        &self,
        fpga_result: &FPGAResult,
        var_map: &HashMap<String, usize>,
    ) -> SampleResult {
        let mut assignments = HashMap::new();

        for (var_name, &idx) in var_map {
            if idx < fpga_result.spins.len() {
                // Convert spin (-1/+1) to binary (0/1)
                assignments.insert(var_name.clone(), fpga_result.spins[idx] > 0);
            }
        }

        SampleResult {
            assignments,
            energy: fpga_result.energy,
            occurrences: 1,
        }
    }
}

#[derive(Debug, Clone)]
struct FPGAResult {
    /// Spin configuration
    spins: Vec<i8>,
    /// Position variables (for SBM)
    positions: Vec<f64>,
    /// Momentum variables (for SBM)
    momenta: Vec<f64>,
    /// Solution energy
    energy: f64,
    /// Number of iterations
    iterations: u32,
}

impl Sampler for FPGASampler {
    fn run_qubo(
        &self,
        model: &(Array2<f64>, HashMap<String, usize>),
        shots: usize,
    ) -> SamplerResult<Vec<SampleResult>> {
        let (qubo, var_map) = model;

        // Check problem size
        if qubo.shape()[0] > self.max_problem_size {
            return Err(SamplerError::InvalidModel(format!(
                "Problem size {} exceeds FPGA capacity {}",
                qubo.shape()[0],
                self.max_problem_size
            )));
        }

        // Execute on FPGA
        let fpga_results = self.execute_on_fpga(qubo, shots)?;

        // Convert results
        let mut results: Vec<SampleResult> = fpga_results
            .iter()
            .map(|r| self.convert_result(r, var_map))
            .collect();

        // Sort by energy
        results.sort_by(|a, b| {
            a.energy
                .partial_cmp(&b.energy)
                .unwrap_or(std::cmp::Ordering::Equal)
        });

        Ok(results)
    }

    fn run_hobo(
        &self,
        _hobo: &(scirs2_core::ndarray::ArrayD<f64>, HashMap<String, usize>),
        _shots: usize,
    ) -> SamplerResult<Vec<SampleResult>> {
        Err(SamplerError::NotImplemented(
            "HOBO not supported by FPGA hardware".to_string(),
        ))
    }
}

impl Drop for FPGASampler {
    fn drop(&mut self) {
        // Clean up FPGA resources
        if let Some(device) = &*self.device.borrow() {
            // Release device
            println!("Releasing FPGA device {}", device.device_id);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_fpga_config() {
        let mut config = FPGAConfig::default();
        assert_eq!(config.clock_frequency, 300);
        assert_eq!(config.parallelism.spin_updaters, 64);

        match config.platform {
            FPGAPlatform::XilinxAlveo { ref model } => {
                assert_eq!(model, "U280");
            }
            _ => panic!("Wrong platform"),
        }
    }

    #[test]
    fn test_max_problem_size() {
        let mut config = FPGAConfig::default();
        let sampler = FPGASampler::new(config);
        assert_eq!(sampler.max_problem_size, 8192);

        let custom_config = FPGAConfig {
            platform: FPGAPlatform::Custom {
                vendor: "Test".to_string(),
                model: "Small".to_string(),
                resources: FPGAResources {
                    logic_elements: 100000,
                    dsp_blocks: 100,
                    on_chip_memory: 10,
                    memory_bandwidth: 10.0,
                },
            },
            ..FPGAConfig::default()
        };

        let custom_sampler = FPGASampler::new(custom_config);
        assert_eq!(custom_sampler.max_problem_size, 1000);
    }
}