29:null 2a:["$","title",null,{"children":"Simple Date Arithmetic | Sébastien Pierre | Observable"}] 2f:T4e3,From [Tomohiko Sakamoto](https://web.archive.org/web/20160617132013/https://wikicoding.org/wiki/c/Tomohiko_Sakamoto%27s_Algorithm/). - Jan 1st 1 AD is a Monday in Gregorian calendar. - Jan 0th 1 AD is a Sunday (It does not exist technically). - Every 4 years we have a leap year. - But xy00 cannot be a leap unless xy divides 4 with remainder 0. - `y/4 - y/100 + y/400` gives the number of leap years from 1AD to the given year. - As each year has 365 days (divides 7 with remainder 1), unless it is a leap year or the date is in Jan or Feb, the day of a given date changes by 1 each year. In other cases, it increases by 2. - `y -= m<3` If the month is neither Jan nor Feb, we do not count the 29th Feb (if it exists) of the given year. - So `y + y/4 - y/100 + y/400` gives the day of Jan 0th (Dec 31st of the previous year) of the year. (This gives the remainder with 7 of the number of days passed before the given year began.) Given an array `t` of tumber of days passed before the month `m+1` begins: - `t[m-1]+d` is the number of days passed in year `y` up to the given date. - `(y + y/4 - y/100 + y/400 + t[m-1] + d) % 7` is remainder of the number of days from Jan 0 1AD to the given date which will be the day (`0=Sunday`,`6=Saturday`). 30:[{"id":"604e9ca05d4403ee0989f57c2f9f11d4f2d94f7b4e2cfac3f08a6b1f538ea0a101ba0414680dce24e20a27a85178ab014b49c3e7cb4bb8fd99bcbef3363aa709","href":"https://static.observableusercontent.com/files/604e9ca05d4403ee0989f57c2f9f11d4f2d94f7b4e2cfac3f08a6b1f538ea0a101ba0414680dce24e20a27a85178ab014b49c3e7cb4bb8fd99bcbef3363aa709","name":"DALL·E 2023-12-04 14.30.29 - A simple architectural blueprint-style illustration depicting the process of converting a calendar date (YEAR_MONTH_DAY) into a numerical value and th.png","type":"image/png","lastModified":1701653447776.758,"size":1799438}] 2d:{"id":"449146d48f5956d6","slug":null,"title":"Simple Date Arithmetic","thumbnail":"49e3b8e7b5c25c76853ac31b4ed41e895e2facb91573182f4e68e995d0ccb899","access_level":"public","create_time":"$D2023-12-04T01:12:31.971Z","update_time":"$D2024-09-17T05:17:41.045Z","view_time":null,"first_public_time":"$D2023-12-04T01:12:31.971Z","fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"cc0ce9489265b441","login":"sebastien","name":"Sébastien Pierre","avatar_url":"https://avatars-next.observableusercontent.com/e328f33fe583d34ba96f68fa91d451af121df97e58a4f7b231c86f5293028a53","tier":"starter_2024"},"version":912,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"7083c0770e4c8937","login":"sebastien","name":"Sébastien Pierre","avatar_url":"https://avatars-next.observableusercontent.com/e328f33fe583d34ba96f68fa91d451af121df97e58a4f7b231c86f5293028a53","tier":null}],"members":[{"type":"individual","id":"7083c0770e4c8937","login":"sebastien","name":"Sébastien Pierre","avatar_url":"https://avatars-next.observableusercontent.com/e328f33fe583d34ba96f68fa91d451af121df97e58a4f7b231c86f5293028a53","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"subscribed":null,"forks":0,"collection":null,"type":"notebook","body":{"title":"Simple Date Arithmetic","cells":[{"id":0,"value":"# Simple Date Arithmetic","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":671,"value":"Working with dates is overly complicated. In this notebook, we introduce a format for managing dates and times as integers, and easily work with them. Having dates as integers makes has advantages for data visualisation and data processing, but the functions introduced here are meant to be of general purpose.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":15,"value":"viewof selectedDate = html``","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":19,"value":"html`\n\n\n\n\n\n

Tuple	`${JSON.stringify([\n selectedDate.getFullYear(),\n selectedDate.getMonth() + 1,\n selectedDate.getDate()\n])}`
Numeric date	`${JSON.stringify(\n datenum(\n selectedDate.getFullYear(),\n selectedDate.getMonth() + 1,\n selectedDate.getDate()\n )\n)}`
Date from numeric	`${JSON.stringify(\n numdate(\n datenum(\n selectedDate.getFullYear(),\n selectedDate.getMonth() + 1,\n selectedDate.getDate()\n )\n )\n)}`
Weekday	`${JSON.stringify(\n WeekDay.names[\n weekday(\n selectedDate.getFullYear(),\n selectedDate.getMonth() + 1,\n selectedDate.getDate()\n )\n ]\n)}`
Local Time zone offset	`${JSON.stringify(\n timezone()\n)}`

`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":94,"value":"## Dates as numbers\n","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":681,"value":"datenum(selectedDate)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":13,"value":"datenum = (y, m = 1, d = 1, h = 0, mn = 0, s = 0) => {\n if (y instanceof Date) {\n s = y.getSeconds();\n mn = y.getMinutes();\n h = y.getHours();\n m = y.getMonth() + 1;\n d = y.getDate();\n y = y.getFullYear();\n }\n return (\n datedays(y, m, d) * by.day.step +\n h * by.hour.step +\n mn * by.minute.step +\n s * by.second.step\n );\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":684,"value":"numdate(datenum(selectedDate))","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":688,"value":"datenum(selectedDate) \n","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":705,"value":" divmul(datenum(selectedDate), by.year.step)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":725,"value":"// Because of pre-gregorian dates, we have discrepancy between the step\n[1000 * by.year.step / by.day.step, datedays(1000)]","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":788,"value":"[1 * by.year.step / by.day.step, datedays(1582+1)-datedays(1582)]","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":823,"value":"datedays(1582)-datedays(1582-1)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":795,"value":"datedays(1582+1)-datedays(1582)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":827,"value":"leapyear(1582)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":828,"value":"","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":814,"value":"datedays(1582+2)-datedays(1582+1)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":810,"value":"datedays(2001)-datedays(2000)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":806,"value":"datedays(1)-datedays(0)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":709,"value":"datedays(2024, 2, 1) - datedays(2023,12,31)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":7,"value":"numdate = (n) => [\n div(n, by.year.step),\n div(n, by.month.step, by.month.period),\n 0\n]\n/*const g = div(n, MS_PER_DAY);\n let y = div(10000 * g + 14780, 3652425);\n let ddd = g - (365 * y + div(y, 4) - div(y, 100) + div(y, 400));\n if (ddd < 0) {\n y = y - 1;\n ddd = g - (365 * y + div(y, 4) - div(y, 100) + div(y, 400));\n }\n let mi = div(100 * ddd + 52, 3060);\n let mm = ((mi + 2) % 12) + 1;\n y = y + div(mi + 2, 12);\n let dd = ddd - div(mi * 306 + 5, 10) + 1;\n return [y, mm, dd];*/","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":486,"value":"datedays = (year, month, day) =>\n // 365 days a year,\n year * 365 +\n // plus one days for every leap year since,\n leaps(year - 1) +\n (month && month > 1 ? (isleap(year) ? LEAP_YEAR_DAYS : YEAR_DAYS)[(month - 1) % 12] : 0) +\n (day > 1 ? day - 1 : 0)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":543,"value":"// Number of leap years between 0AD and the given year, inclusively.\nleaps = (year) =>\n !year || year < 0\n ? 0\n : // Gregorian calendar\n Math.floor(year / 4) -\n Math.floor(year / 100) +\n Math.floor(year / 400) -\n // adjustment for missing leap years in 100, 200, 300, 500, 600, 700, 900, 1000, 1100, 1400\n (year >= 1582 ? 10 : 0)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":103,"value":"`date(n)` converts the given datenum `n` or `Date` into an `[y,m,d]` array, `date(y,m,d)` returns the date as `[y,m,d]-.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":187,"value":"date = (y,m=undefined,d=undefined) => (\n m === undefined && d === undefined && typeof (y === \"number\") && y >= 86400000 ? datenum.date(y) : y instanceof Date ? [y.getFullYear(), y.getMonth()+1, y.getDate()] : [y, m||1, d||1]\n \n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":531,"value":"15638400000 / 31557600000","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":533,"value":"((datedays(2024, 3, 28) - datedays(2024)) * by.day.step) / by.month.step","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":664,"value":"datedays(2024, 1, 1) - datedays(2023, 12, 31)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":635,"value":"div(datenum(2024, 1, 28), by.month.step, by.month.period, by.month.offset) + 1","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":625,"value":"div(\n datenum(2024, 3, 28) - datenum(2024),\n by.month.step,\n by.month.period,\n by.month.offset\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":579,"value":"{\n const year = 2024;\n const month = 0;\n const day = 0;\n return (\n (year - 1) * 365 +\n // plus one days for every leap year since,\n leaps(year - 1)\n );\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":199,"value":"## Granularity","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":421,"value":"We define the granularity of time using the following attributes:\n- The `step`, which is how many milliseconds (on average) each step takes. This is straightforward for simply periodic values, but for months and years the value depends on a more complicated logic (based on the rhythm of leap years)\n- The `period`, which determines how many values go in a period.\n- The `offset` indicates the first value. For months it's `1` so that you can have a month `12` with a period of `12`\n- The `index` which is the index of the value in a timetuple array like `[year,month,day,...]`\n- The `suffix`, which is the typical suffixed used for display","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":411,"value":"{\n const fields = Object.keys(\n Object.keys(by).reduce((r, k) => Object.assign(r, by[k]), {})\n );\n return $table(\n [\"Field\", ...fields],\n ...Object.keys(by).map((k) => [k, ...fields.map((_) => by[k][_])])\n );\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":830,"value":"Second = ({ index: 6, step: 1_000, offset: 0, suffix: \"s\", period: 60 }) ","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":834,"value":"Minute = ({ index: 5, step: 1_000 * 60, offset: 0, suffix: \"m\", period: 60 })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":841,"value":"Hour = ({ index: 4, step: 1_000 * 60 * 60, offset: 0, suffix: \"h\", period: 24 })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":844,"value":"Day = ({\n index: 3,\n step: 1_000 * 60 * 60 * 24,\n offset: 1,\n suffix: \"d\",\n period: 30.4375\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":847,"value":"Week = ({ index: 2, step: 1_000 * 60 * 60 * 24 * 7, offset: 1, suffix: \"w\" })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":850,"value":"Month = (/* \n sum([31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31] * 3 + [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]) / (12*4) \n >>> 1_000*60*60*24/ 48.0\n 1800000.0\n >>> 1_000*60*30\n 1800000\n */\n{ index: 1, step: 1461 * 1800000, period: 12, offset: 1, suffix: \"M\" })","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":854,"value":"Year = ({\n index: 0,\n step: (365 * 3 + 366) * 1_000 * 60 * 60 * 6 /* 24/4 === 6 */,\n offset: 0,\n suffix: \"Y\"\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":201,"value":"by = Object.freeze({\n second: Second,\n minute: Minute ,\n hour: Hour,\n day: Day,\n week: Week,\n month: Month,\n year: Year,\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":878,"value":"{\n const today = new Date().getTime() + Year.step * 1970;\n const daysInYear = today % Year.step;\n\n return md`\n| Grain | Units |\n| :------- | :----- |\n| Seconds per minute | \\`${Minute.step / Second.step}\\` |\n| Minutes per hour | \\`${Hour.step / Minute.step}\\` |\n| Hours per day | \\`${Day.step / Hour.step}\\` |\n| Days per month | \\`${Month.step / Day.step}\\` |\n| Days per year | \\`${Year.step / Day.step}\\` |\n| Months per year | \\`${Year.step / Month.step}\\` |\n| Years since EPOCH | \\`${new Date(0).getTime() / Year.step}\\` |\n| Year from today since EPOCH | \\`${new Date().getTime() / Year.step}\\` \n| Current Year | \\`${today / Year.step}\\` \n| Days in Year | \\`${daysInYear / Day.step}\\`\n| Current Month | \\`${((today / Month.step) % Month.period) + Month.offset}\\` \n| Current Day | \\`${((daysInYear * 1000) % (Day.period * 1000)) / 1000}\\` \n`;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":866,"value":"viewof periodDate = html``","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":868,"value":"{\n const origin = new Date(0);\n const delta = periodDate.getTime() - origin.getTime();\n return Object.keys(by).reduce((r, grain) => {\n const g = by[grain];\n let v = Math.floor(delta / g.step);\n let w = (g.period ? v % g.period : v) + (g.offset || 0);\n r[grain] = `${w}${g.suffix}`;\n return r;\n }, {});\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":429,"value":"Noting here that the steps for `months` and `years` are calculated as follows:\n- For **months**, we calculate the average duration of a month over 4 years (we consider the turn of century non leap year negligible). A normal year has `365` days, a leap year has `366`, so the average is `(365*3+366)/4/12=${(365*3+366)/4/12}`, which then multiplied by the value of day is `${((365*3+366)/4/12)*by.day.step}`\n- For **years** it's the same with the number of days `(365*3+366)/4=${(365*3+366)/4}`, which then multiplied by the value of day is `${((365*3+366)/4)*by.day.step}`","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":242,"value":"## Snapping","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":275,"value":"snap = (nd, grain) => {\n switch (grain) {\n default:\n return divmul(nd, grain.value);\n }\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":395,"value":"_snapDate = datenum(2024, 7, 12, 17, 52, 38)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":355,"value":"$$table(\n [\"Date\", numdate(_snapDate)],\n [\"Year\", datenum(_snapDate)],\n [\n \"Year\",\n divmul(_snapDate, by.year.step),\n numdate(divmul(_snapDate, by.year.step))\n ],\n [\n \"Month\",\n divmul(_snapDate, by.month.step),\n numdate(divmul(_snapDate, by.month.step))\n ],\n [\n \"Week\",\n divmul(_snapDate, by.week.step),\n numdate(divmul(_snapDate, by.week.step))\n ],\n [\n \"Day\",\n divmul(_snapDate, by.day.step),\n numdate(divmul(_snapDate, by.day.step))\n ],\n [\n \"Hour\",\n divmul(_snapDate, by.hour.step),\n numdate(divmul(_snapDate, by.hour.step))\n ]\n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":365,"value":"numdate(63865216800000)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":284,"value":"snap(datenum(2024, 7, 15, 5, 21), by.day)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":300,"value":"dt0 = datenum(2024, 7, 15, 5, 21) - datenum(2024, 7, 14)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":304,"value":"63883036800000 / 86400000","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":250,"value":"## Delta\n","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":254,"value":"dist = (d0, d1=undefined) => {\n // Just one argument, we break down by granularity and return the result\n if (d1 === undefined) {\n const res={};\n for (k of by) {\n res[k] = d0/ by[k].period;\n }\n return res;\n } else {\n const dt = d1 - d0;\n const ds = dt % by.second.period;\n const dM =\n }\n \n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":107,"value":"## Leap years\n","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":495,"value":"Leap years is sort of periodical, and what defines the number of days since 0AD for a given year. Calculating the distance in days since year 0 is the basis of our date calculation.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":88,"value":"isleap = (year) =>\n year < 0 || year % 4 !== 0\n ? false\n : year <= 1582\n ? year % 4 === 0\n : (year % 4 === 0) && (year % 100 !== 0 || year % 400 === 0)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":222,"value":"// Returns the number of days in the year, or since the beginning of the year if the days was given\nyeardays = (year, month) =>\n month === undefined\n ? isleap(year)\n ? 366\n : 365\n : isleap(year)\n ? YEAR_DAYS[month - 1]\n : LEAP_YEAR_DAYS[month - 1]","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":227,"value":"monthdays = (year, month) =>\n month === 2 ? (isleap(year) ? 29 : 28) : month % 2 === 0 ? 30 : 31","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":207,"value":"## Week Day","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":109,"value":"$2f","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":111,"value":"weekday = (year, month, day, firstDay = 0) => {\n const s = div(year, 100);\n let sday =\n 1720996.5 -\n s +\n div(s, 4) +\n Math.floor(365.25 * year) +\n Math.floor(30.6001 * (month + 1)) +\n day;\n sday -= div(sday, 7) * 7;\n const wday = (Math.floor(sday) + 1) % 7;\n // We adjust based on the first day. In US calendars, the first day\n // is Sunday (==6), so we shift the result by one day, as there\n // is now 1 more day to reach Monday (the canonical 0).\n return (wday + (7 - firstDay)) % 7;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":114,"value":"WeekDay = Enum(\n \"Monday\",\n \"Tuesday\",\n \"Wednesday\",\n \"Thursday\",\n \"Friday\",\n \"Saturday\",\n \"Sunday\"\n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":84,"value":"## Timezones","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":90,"value":"\n// The timezone offset is in milliseconds, the same unit as `datenum`\ntimezone = () => new Date().getTimezoneOffset() * MS_PER_MINUTE","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":502,"value":"## Constants","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":163,"value":"MS_PER_MINUTE = 1000 * 60","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":145,"value":"// We want to stay in integer divisions, where the baseline is the millisecond. This is the value that represents a day.\nMS_PER_DAY = 1000 * 60 * 60 * 24","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":504,"value":"YEAR_MONTHS = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":510,"value":"YEAR_DAYS = YEAR_MONTHS.reduce(\n (r, v, i) => ((r[i] = i === 0 ? 0 : r[i - 1] + YEAR_MONTHS[i - 1]), r),\n new Array(12)\n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":506,"value":"LEAP_YEAR_MONTHS = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":514,"value":"LEAP_YEAR_DAYS = YEAR_MONTHS.reduce(\n (r, v, i) => ((r[i] = i === 0 ? 0 : r[i - 1] + YEAR_MONTHS[i - 1]), r),\n new Array(12)\n)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":92,"value":"## Utilities\n","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":80,"value":"All divisions need to be *integer division*, so we introduce `div` for readability.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":39,"value":"div = (v, k, p, offset = 0) =>\n p ? ((Math.floor(v / k) - offset) % p) + offset : Math.floor(v / k)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":278,"value":"divmul = (v, k) => div(v, k) * k","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":359,"value":"$$table = (...rows) => html`\n${rows\n .map(\n ([header, ...cols]) =>\n `${cols.map(v=>``).join(\"\")}`\n )\n .join(\"\")}

${header}	`${JSON.stringify(v)}`

`","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":382,"value":"","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":118,"value":"Enum = (...names) =>(\n {values:Object.freeze(names.reduce((r,v,i)=>(\n r[v] = i, r\n ), {})),names}\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined"},{"id":351,"value":"## References\n","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"},{"id":353,"value":"- The core arithmetic is based on Gary Katch date algorithm presenter [here](https://web.archive.org/web/20170507133619/https://alcor.concordia.ca/~gpkatch/gdate-algorithm.html) with the supporting method [here](https://web.archive.org/web/20161203020157/http://alcor.concordia.ca/~gpkatch/gdate-method.html)\n- The week day algorithm is based on (Tomohiko Sakamoto's algorithm)[https://web.archive.org/web/20160617132013/https://wikicoding.org/wiki/c/Tomohiko_Sakamoto%27s_Algorithm/]","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined"}],"files":"$W30","stdlib":"1","titling":"auto"}} 2e:"$2d:body"