Function histogram

packages/effect/src/internal/metric/hook.ts:139–218

(key: MetricKey.MetricKey.Histogram)

/** @internal */
export const histogram = (key: MetricKey.MetricKey.Histogram): MetricHook.MetricHook.Histogram => {
  const bounds = key.keyType.boundaries.values
  const size = bounds.length
  const values = new Uint32Array(size + 1)
  // NOTE: while 64-bit floating point precision shoule be enough for any
  // practical histogram boundary values, there is still a small chance that
  // precision will be lost with very large / very small numbers. If we find
  // that is the case, a more complex approach storing the histogram boundary
  // values as a tuple of `[original: string, numeric: number]` may be warranted
  const boundaries = new Float64Array(size)
  let count = 0
  let sum = 0
  let min = Number.MAX_VALUE
  let max = Number.MIN_VALUE

  pipe(
    bounds,
    Arr.sort(number.Order),
    Arr.map((n, i) => {
      boundaries[i] = n
    })
  )

  // Insert the value into the right bucket with a binary search
  const update = (value: number) => {
    let from = 0
    let to = size
    while (from !== to) {
      const mid = Math.floor(from + (to - from) / 2)
      const boundary = boundaries[mid]
      if (value <= boundary) {
        to = mid
      } else {
        from = mid
      }
      // The special case when to / from have a distance of one
      if (to === from + 1) {
        if (value <= boundaries[from]) {
          to = from
        } else {
          from = to
        }
      }
    }
    values[from] = values[from]! + 1
    count = count + 1
    sum = sum + value
    if (value < min) {
      min = value
    }
    if (value > max) {
      max = value
    }
  }

  const getBuckets = (): ReadonlyArray<readonly [number, number]> => {
    const builder: Array<readonly [number, number]> = Arr.allocate(size) as any
    let cumulated = 0