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hellerve merged 1 commit into from
Aug 26, 2026
Merged

Compute UNIX timestamps in Long so they do not wrap past 2038 #27

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4 changes: 2 additions & 2 deletions docs/Datetime.html
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Original file line number Diff line number Diff line change
Expand Up @@ -411,7 +411,7 @@ <h3 id="from-unix-timestamp">
defn
</div>
<p class="sig">
(Fn [Int] Datetime)
(Fn [Long] Datetime)
</p>
<pre class="args">
(from-unix-timestamp ts)
Expand Down Expand Up @@ -1253,7 +1253,7 @@ <h3 id="to-unix-timestamp">
defn
</div>
<p class="sig">
(Fn [(Ref Datetime a)] Int)
(Fn [(Ref Datetime a)] Long)
</p>
<pre class="args">
(to-unix-timestamp dt)
Expand Down
86 changes: 68 additions & 18 deletions test/time.carp
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,21 @@
(let [billion (Uint64.from-long 1000000000l)]
(+ (* (Uint64.from-long secs) billion) (Uint64.from-long ns))))

; a Datetime with a time-of-day and no timezone.
(defn at [y mo d h mi s]
(Datetime.init y
mo
d
(Maybe.Just h)
(Maybe.Just mi)
(Maybe.Just s)
(Maybe.Nothing)
(Maybe.Nothing)))

; seconds since the epoch, from a day count and a time of day (see `nanos`).
(defn epoch-at [days tod]
(+ (* (Long.from-int days) 86400l) (Long.from-int tod)))

; n UTF-8 continuation bytes, which decode to no character at all.
(defn conts [n] (String.from-bytes &(Array.replicate n &128b)))

Expand Down Expand Up @@ -257,7 +272,7 @@
"different dates are not equal")

(assert-equal test
0
0l
(Datetime.to-unix-timestamp
&(Datetime.init 1970
1
Expand All @@ -271,7 +286,7 @@
; midnight EST (UTC-5) is 05:00 UTC, i.e. 18000 seconds past the epoch; the
; timezone offset must be subtracted from the wall-clock, not added
(assert-equal test
18000
18000l
(Datetime.to-unix-timestamp
&(Datetime.init 1970
1
Expand All @@ -284,7 +299,7 @@
"to-unix-timestamp subtracts a negative (west-of-UTC) offset")
; 1970-01-02 00:00 at UTC+5 is 1970-01-01 19:00 UTC = 86400 - 18000 = 68400
(assert-equal test
68400
68400l
(Datetime.to-unix-timestamp
&(Datetime.init 1970
1
Expand All @@ -304,7 +319,7 @@
(Maybe.Just 0)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 0)
&(Datetime.from-unix-timestamp 0l)
"from-unix-timestamp 0 is epoch")
; Feb 29 leap year round-trip (1972 is a leap year, ts = 68169600)
(assert-equal test
Expand Down Expand Up @@ -353,7 +368,7 @@
; is one non-leap year (365 days) past the epoch; this input previously
; SIGABRTed in both directions.
(assert-equal test
31536000
31536000l
(Datetime.to-unix-timestamp
&(Datetime.init 1971
1
Expand All @@ -373,12 +388,12 @@
(Maybe.Just 0)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 31536000)
&(Datetime.from-unix-timestamp 31536000l)
"from-unix-timestamp of 1971-01-01")
; 2023-12-31 23:59:59 (one second before 2024) previously produced a day-ZERO
; date of 2024-1-0
(assert-equal test
1704067199
1704067199l
(Datetime.to-unix-timestamp
&(Datetime.init 2023
12
Expand All @@ -398,11 +413,11 @@
(Maybe.Just 59)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 1704067199)
&(Datetime.from-unix-timestamp 1704067199l)
"from-unix-timestamp of 2023-12-31 23:59:59")
; 1000000000 is 2001-09-09 01:46:40 UTC
(assert-equal test
1000000000
1000000000l
(Datetime.to-unix-timestamp
&(Datetime.init 2001
9
Expand All @@ -422,11 +437,11 @@
(Maybe.Just 40)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 1000000000)
&(Datetime.from-unix-timestamp 1000000000l)
"from-unix-timestamp of 2001-09-09 01:46:40")
; the 32-bit time_t maximum: 2038-01-19 03:14:07 UTC = 2147483647
(assert-equal test
2147483647
2147483647l
(Datetime.to-unix-timestamp
&(Datetime.init 2038
1
Expand All @@ -446,12 +461,47 @@
(Maybe.Just 7)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 2147483647)
&(Datetime.from-unix-timestamp 2147483647l)
"from-unix-timestamp at the 32-bit boundary")
(assert-equal test
(+ (Long.from-int Int.MAX) 1l)
(Datetime.to-unix-timestamp &(at 2038 1 19 3 14 8))
"to-unix-timestamp one second past the 32-bit maximum")
(assert-equal test
&@"2038-01-19 03:14:08"
&(stamp &(Datetime.from-unix-timestamp (+ (Long.from-int Int.MAX) 1l)))
"from-unix-timestamp one second past the 32-bit maximum")
; 2100-01-01 is 47482 days past the epoch, 2262-04-11 is 106751
(assert-equal test
(epoch-at 47482 0)
(Datetime.to-unix-timestamp &(at 2100 1 1 0 0 0))
"to-unix-timestamp of 2100-01-01")
(assert-equal test
&@"2100-01-01 00:00:00"
&(stamp &(Datetime.from-unix-timestamp (epoch-at 47482 0)))
"from-unix-timestamp of 2100-01-01")
(assert-equal test
(epoch-at 106751 0)
(Datetime.to-unix-timestamp &(at 2262 4 11 0 0 0))
"to-unix-timestamp of 2262-04-11")
(assert-equal test
&@"2262-04-11 12:34:56"
&(stamp
&(Datetime.from-unix-timestamp
(Datetime.to-unix-timestamp &(at 2262 4 11 12 34 56))))
"from-unix-timestamp round-trips a date past 2038")
(assert-equal test
(- (Long.from-int Int.MIN) 1l)
(Datetime.to-unix-timestamp &(at 1901 12 13 20 45 51))
"to-unix-timestamp one second before the 32-bit minimum")
(assert-equal test
&@"1901-12-13 20:45:51"
&(stamp &(Datetime.from-unix-timestamp (- (Long.from-int Int.MIN) 1l)))
"from-unix-timestamp one second before the 32-bit minimum")
; negative timestamps (pre-1970). / and mod truncate toward zero in Carp, so
; the time-of-day must be floored to stay in 0..86399.
(assert-equal test
-1
-1l
(Datetime.to-unix-timestamp
&(Datetime.init 1969
12
Expand All @@ -471,7 +521,7 @@
(Maybe.Just 59)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp -1)
&(Datetime.from-unix-timestamp -1l)
"from-unix-timestamp of -1 is one second before the epoch")
(assert-equal test
&(Datetime.init 1969
Expand All @@ -482,7 +532,7 @@
(Maybe.Just 0)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp -86400)
&(Datetime.from-unix-timestamp -86400l)
"from-unix-timestamp of -86400 is exactly one day before the epoch")
(assert-equal test
&(Datetime.init 1969
Expand All @@ -507,7 +557,7 @@
; leap-day boundary, cross-checked against known UTC values: 1972-02-29 is
; 68169600 and the following day 1972-03-01 is exactly 86400 seconds later
(assert-equal test
68169600
68169600l
(Datetime.to-unix-timestamp
&(Datetime.init 1972
2
Expand All @@ -527,10 +577,10 @@
(Maybe.Just 0)
(Maybe.Nothing)
(Maybe.Nothing))
&(Datetime.from-unix-timestamp 68169600)
&(Datetime.from-unix-timestamp 68169600l)
"from-unix-timestamp of the leap day 1972-02-29")
(assert-equal test
68256000
68256000l
(Datetime.to-unix-timestamp
&(Datetime.init 1972
3
Expand Down
11 changes: 7 additions & 4 deletions time.carp
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Original file line number Diff line number Diff line change
Expand Up @@ -382,15 +382,18 @@ a UNIX timestamp, i.e. the number of seconds elapsed since the 1st of January,
mm (Maybe.from @(minutes dt) 0)
ss (Maybe.from @(seconds dt) 0)]
(-
(+ (* days DAY) (+ (* hh HOUR) (+ (* mm MINUTE) ss)))
(Long.to-int @(Timezone.delta &tz)))))
(+
(* (Long.from-int days) (Long.from-int DAY))
(Long.from-int (+ (* hh HOUR) (+ (* mm MINUTE) ss))))
@(Timezone.delta &tz))))

(doc from-unix-timestamp "returns the `Datetime` equivalent to the UNIX
timestamp `ts`, i.e. the number of seconds elapsed since the 1st of January,
1970.")
(defn from-unix-timestamp [ts]
(let-do [days (/ ts DAY)
secs (- ts (* days DAY))]
(let-do [day-secs (Long.from-int DAY)
days (Long.to-int (/ ts day-secs))
secs (Long.to-int (- ts (* (Long.from-int days) day-secs)))]
; / and mod truncate toward zero, so a negative ts can leave secs
; negative; borrow a day so the time-of-day stays in 0..86399
(when-do (< secs 0) (set! days (Int.dec days)) (set! secs (+ secs DAY)))
Expand Down