Struct ValueTextCache 

pub(crate) struct ValueTextCache {
    pub(crate) slots: Vec<ValueSlot>,
    pub(crate) formula: CalibrationFormula,
    pub(crate) generation: u32,
    pub(crate) lookups: u32,
    pub(crate) hits: u32,
    pub(crate) bypass: u32,
}

Remembers the raw_value,calibrated_value text of recently written raw values.

Values come from a 16-bit converter and repeat heavily (the archive stores them dictionary-encoded), while formatting two f64 with Display is the largest cost of a CSV row. This direct-mapped table, keyed by the raw value’s bits under the current calibration formula, lets a repeated value be copied instead. The text is exactly what write!(out, "{raw},{calibrated}") produces, because a cached entry is that output, and a calibrated value is a pure function of the raw bits and the formula’s coefficients (compared bit for bit, so -0.0 and 0.0 coefficients are different formulas). A different formula starts a new generation, which empties the table without touching it. Data with few repeats (a wide-ranging signal) would only pay for the lookups, so after a window of VALUE_CACHE_WINDOW lookups with fewer than a quarter hits the table is bypassed for VALUE_CACHE_BYPASS rows.

Fields

slots: Vec<ValueSlot>

Slots, allocated on first use.

formula: CalibrationFormula

Formula the current generation’s texts were calibrated with.

generation: u32

Current generation, never 0.

lookups: u32

Lookups in the current window.

hits: u32

Hits in the current window.

bypass: u32

Rows still to format without the table.

Implementations

impl ValueTextCache

pub(crate) fn new() -> Self

Creates an empty cache.

pub(crate) fn write( &mut self, out: &mut Vec<u8>, raw: f64, spec: &CalibrationSpec, ) -> usize

Appends {raw},{calibrated} to out, calibrated being formula applied to raw.

Returns

Where the calibrated text starts in out; it runs to the end of out.