//! Prefetch locality hints for cache optimization.

use super::geometry::{TcbGeometry, TcbLevel};

/// Prefetch locality hint

#[derive(Debug, Clone, Copy)]

pub enum PrefetchLocality {

    /// Non-temporal (streaming, evict soon)

    NonTemporal,

    /// L3 cache

    T2,

    /// L2 cache

    T1,

    /// L1 cache (highest priority)

    T0,

}

/// Calculate optimal prefetch distance based on tile geometry and cache level

///

/// Per Ding & Kennedy (2004): distance = memory_latency / compute_time_per_iter

#[must_use]

pub fn optimal_prefetch_distance(geometry: &TcbGeometry, level: TcbLevel) -> usize {

    // Approximate cycles per micro-tile

    let compute_cycles = geometry.m as usize * geometry.n as usize * geometry.k as usize / 8;

    // Memory latency in cycles (approximate for modern x86)

    let mem_latency = match level {

        TcbLevel::Micro => 4,    // L1: ~4 cycles

        TcbLevel::Midi => 12,   // L2: ~12 cycles

        TcbLevel::Macro => 40,  // L3: ~40 cycles

    };

    // Distance = latency / compute_time, minimum 1

    (mem_latency / compute_cycles.max(1)).max(1)

}