Struct Histogram 

pub struct Histogram<V> {
    pub name: &'static str,
    pub unit: &'static str,
    pub description: &'static str,
    /* private fields */
}

A histogram instrument with branchless base-2 exponential bucket pick.

32 buckets span [2^-10, 2^22) — roughly [0.001, 4_000_000). Values outside that range saturate to bucket 0 or bucket 31. V is the observed value type: f64 for latencies/sizes, u64 for counts.

v1 baseline: single bucket slab per instrument; tag identity is accepted for API symmetry but not accumulated. C9 will shard by attr-set.

Fields

name: &'static str

unit: &'static str

description: &'static str

Implementations

impl<V> Histogram<V>

pub const fn new(name: &'static str) -> Self

pub const fn unit(self, unit: &'static str) -> Self

pub const fn description(self, desc: &'static str) -> Self

pub const fn exponential_base(self, base: f64) -> Self

Set the exponential base. Only 2.0 is supported for the branchless bucket pick; other bases will fall back to bucket 0.

pub const fn exponential_min(self, min: f64) -> Self

Set the lower bound of bucket 0 (must be a power of 2 for the fast path).

pub fn count(&self) -> u64

Return the total observation count.

pub fn sum(&self) -> f64

Return the running sum as f64.

pub fn bucket_snapshot(&self) -> [u64; 32]

Return a snapshot of per-bucket counts.

pub fn snapshot_and_reset(&self) -> (u64, u64, [u64; 32])

Snapshot all state (count, sum_bits, bucket counts) and reset atomics to zero.

Called by the drainer at snapshot time. Each atomic is swapped to 0 — any observations racing the swap appear in the NEXT snapshot window (not lost).

impl Histogram<f64>

pub fn record(&self, value: f64)

Record an f64 observation. Negative values are treated as their absolute magnitude for bucket assignment.

impl Histogram<u64>

pub fn record(&self, value: u64)

Record a u64 observation (cast to f64 for bucket assignment).