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Fix tick.alpha.interval/divide-by #206

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Merged
henryw374 merged 2 commits into from
Nov 19, 2025
Merged

Fix tick.alpha.interval/divide-by #206

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6c2ca5a
Add test for ti/divide-by failure from issue #203
dgr Nov 18, 2025
776ac67
Fix ti/divide-by (divide-by-divisor) #203
dgr Nov 18, 2025
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31 changes: 29 additions & 2 deletions src/tick/alpha/interval.cljc
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Original file line number Diff line number Diff line change
Expand Up @@ -706,8 +706,35 @@
;; Bound by given interval, last will become a remainder.
(map (juxt identity #(t/min (p/forward-duration % period) (t/end ival))))))

(defn divide-by-divisor [ival divisor]
(divide-by-duration ival (cljc.java-time.duration/divided-by (t/duration ival) divisor)))
(defn divide-by-divisor
"Divides the interval specified by `ival` into `divisor` spaced
intervals. The `divisor` must be a positive integer. The calculated
subintervals are exact down to the nearest nanosecond."
[ival divisor]
(assert (pos? divisor))
(assert (integer? divisor))
(let [total-nanos (t/nanos (t/duration ival))
original-beginning (:tick/beginning ival)]
;; Note the algorithm here. We do not calculate a constant
;; duration for each sub-interval. That ends up truncating
;; fractional nanoseconds which can cause us problems with the
;; last interval if we just add the durations togther n
;; times. Instead, we calculate the total duration of the original
;; interval in nanoseconds and compute the ending point of each
;; subinterval as i/n * total duration. The duration of each
;; sub-interval may differ by plus/minus one nanosecond, but the
;; ending point is exactly the end of the original interval (i.e.,
;; n/n * total duration = 1 * total duration = total duration).
(loop [i 1
sub-intervals []
beginning original-beginning]
(let [duration-to-end (t/new-duration (/ (* i total-nanos) divisor) :nanos)
end (t/>> original-beginning duration-to-end)]
(if (= i divisor)
(clojure.core/conj sub-intervals [beginning end])
(recur (inc i)
(clojure.core/conj sub-intervals [beginning end])
end))))))

(defprotocol IDivisibleInterval
(divide-interval [divisor ival] "Divide an interval by a given divisor"))
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6 changes: 5 additions & 1 deletion test/tick/alpha/interval_test.cljc
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Original file line number Diff line number Diff line change
Expand Up @@ -717,7 +717,11 @@
(is (= 2 (count (ti/divide-by t/year-month (ti/bounds (t/date "2017-09-10") (t/date "2017-10-10"))))))
(is (= 3 (count (ti/divide-by t/year (ti/bounds (t/date-time "2017-09-10T12:00") (t/year "2019"))))))
(is (= 3 (count (ti/divide-by t/year (ti/bounds (t/date-time "2017-09-10T12:00") (t/year-month "2019-02"))))))
(is (= 24 (count (ti/divide-by (t/new-duration 1 :hours) (t/date "2017-09-10"))))))
(is (= 24 (count (ti/divide-by (t/new-duration 1 :hours) (t/date "2017-09-10")))))
;; Issue #203
(is (= 17 (count (ti/divide-by 17
(ti/new-interval #time/zoned-date-time "2025-07-09T09:33-04:00"
#time/zoned-date-time "2025-07-09T14:30-04:00"))))))

;; TODO: Divide by duration

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