Struct CacheCostParams 

pub struct CacheCostParams {
    pub c_miss_us: f64,
    pub c_mem_per_byte: f64,
    pub item_bytes: f64,
    pub working_set_n: f64,
    pub zipf_alpha: f64,
    pub budget_max_bytes: f64,
}

Parameters for the glyph/cell cache cost model.

Fields

c_miss_us: f64

Cost of a cache miss in µs (rasterize + upload).

c_mem_per_byte: f64

Opportunity cost per byte of atlas memory (µs/byte/frame).

item_bytes: f64

Average item size in bytes (slot area including padding).

working_set_n: f64

Working set size (number of distinct glyphs in a typical session).

zipf_alpha: f64

Zipf exponent for access frequency distribution. α > 1 means heavy-tail (few glyphs dominate); typical terminal ≈ 1.2–1.8.

budget_max_bytes: f64

Maximum allowed cache budget in bytes.

Implementations

impl CacheCostParams

pub fn miss_rate(&self, budget_bytes: f64) -> f64

Compute the miss rate under LRU with IRM/Zipf workload.

Approximation: miss_rate(B) ≈ 1 − min(1, (capacity / N))^(1/α) where capacity = B / item_bytes.

pub fn total_cost(&self, budget_bytes: f64) -> f64

Total cost J(B) = c_miss × miss_rate(B) × N_accesses + c_mem × B.

We normalize to per-frame cost assuming working_set_n accesses/frame.

pub fn evaluate(&self, budget_bytes: f64) -> CacheCostPoint

Evaluate a single point on the cost surface.

pub fn optimal_budget(&self) -> f64

Compute the optimal cache budget analytically.

From dJ/dB = 0:

B* = item_bytes × N × (c_miss / (α × c_mem_per_byte × item_bytes × N))^(α/(1+α))

clamped to [item_bytes, budget_max_bytes].

pub fn optimize(&self) -> CacheCostResult

Run the full optimization and produce evidence.

Trait Implementations

impl Clone for CacheCostParams

fn clone(&self) -> CacheCostParams

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for CacheCostParams

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for CacheCostParams

fn default() -> Self

Returns the “default value” for a type.