Editorial: Move regulating and balancing logic into ISODateSurpasses

polyfill/lib/calendar.mjs

@@ -131,7 +131,19 @@ function calendarDateWeekOfYear(id, isoDate) {
   return { week: woy, year: yow };
 }
 
-function ISODateSurpasses(sign, y1, m1, d1, isoDate2) {
+function ISODateSurpasses(sign, baseDate, isoDate2, years, months, weeks, days) {
+  const yearMonth = ES.BalanceISOYearMonth(baseDate.year + years, baseDate.month + months);
+  let y1 = yearMonth.year;
+  let m1 = yearMonth.month;
+  let d1 = baseDate.day;
+  if (weeks !== 0 || days !== 0) {
+    const regulatedDate = ES.RegulateISODate(y1, m1, d1, 'constrain');
+    ({
+      year: y1,
+      month: m1,
+      day: d1
+    } = ES.BalanceISODate(regulatedDate.year, regulatedDate.month, regulatedDate.day + 7 * weeks + days));
+  }
   if (y1 !== isoDate2.year) {
     if (sign * (y1 - isoDate2.year) > 0) return true;
   } else if (m1 !== isoDate2.month) {
@@ -192,25 +204,22 @@ impl['iso8601'] = {
 
     let years = 0;
     let months = 0;
-    let intermediate;
     if (largestUnit === 'year' || largestUnit === 'month') {
       // We can skip right to the neighbourhood of the correct number of years,
       // it'll be at least one less than two.year - one.year (unless it's zero)
       let candidateYears = two.year - one.year;
       if (candidateYears !== 0) candidateYears -= sign;
       // loops at most twice
-      while (!ISODateSurpasses(sign, one.year + candidateYears, one.month, one.day, two)) {
+      while (!ISODateSurpasses(sign, one, two, candidateYears, 0, 0, 0)) {
         years = candidateYears;
         candidateYears += sign;
       }
 
       let candidateMonths = sign;
-      intermediate = ES.BalanceISOYearMonth(one.year + years, one.month + candidateMonths);
       // loops at most 12 times
-      while (!ISODateSurpasses(sign, intermediate.year, intermediate.month, one.day, two)) {
+      while (!ISODateSurpasses(sign, one, two, years, candidateMonths, 0, 0)) {
         months = candidateMonths;
         candidateMonths += sign;
-        intermediate = ES.BalanceISOYearMonth(intermediate.year, intermediate.month + sign);
       }
 
       if (largestUnit === 'month') {
@@ -219,7 +228,7 @@ impl['iso8601'] = {
       }
     }
 
-    intermediate = ES.BalanceISOYearMonth(one.year + years, one.month + months);
+    const intermediate = ES.BalanceISOYearMonth(one.year + years, one.month + months);
     const constrained = ES.ConstrainISODate(intermediate.year, intermediate.month, one.day);
 
     let weeks = 0;

spec/calendar.html

@@ -563,34 +563,26 @@ <h1>
           1. Let _years_ be 0.
           1. If _largestUnit_ is ~year~, then
             1. Let _candidateYears_ be _sign_.
-            1. Repeat, while ISODateSurpasses(_sign_, _one_.[[Year]] + _candidateYears_, _one_.[[Month]], _one_.[[Day]], _two_) is *false*,
+            1. Repeat, while ISODateSurpasses(_sign_, _one_, _two_, _candidateYears_, 0, 0, 0) is *false*,
               1. Set _years_ to _candidateYears_.
               1. Set _candidateYears_ to _candidateYears_ + _sign_.
           1. Let _months_ be 0.
           1. If _largestUnit_ is ~year~ or _largestUnit_ is ~month~, then
             1. Let _candidateMonths_ be _sign_.
-            1. Let _intermediate_ be BalanceISOYearMonth(_one_.[[Year]] + _years_, _one_.[[Month]] + _candidateMonths_).
-            1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _one_.[[Day]], _two_) is *false*,
+            1. Repeat, while ISODateSurpasses(_sign_, _one_, _two_, _years_, _candidateMonths_, 0, 0) is *false*,
               1. Set _months_ to _candidateMonths_.
               1. Set _candidateMonths_ to _candidateMonths_ + _sign_.
-              1. Set _intermediate_ to BalanceISOYearMonth(_intermediate_.[[Year]], _intermediate_.[[Month]] + _sign_).
-          1. Set _intermediate_ to BalanceISOYearMonth(_one_.[[Year]] + _years_, _one_.[[Month]] + _months_).
-          1. Let _constrained_ be ! RegulateISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _one_.[[Day]], ~constrain~).
           1. Let _weeks_ be 0.
           1. If _largestUnit_ is ~week~, then
             1. Let _candidateWeeks_ be _sign_.
-            1. Set _intermediate_ to BalanceISODate(_constrained_.[[Year]], _constrained_.[[Month]], _constrained_.[[Day]] + 7 × _candidateWeeks_).
-            1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]], _two_) is *false*,
+            1. Repeat, while ISODateSurpasses(_sign_, _one_, _two_, _years_, _months_, _candidateWeeks_, 0) is *false*,
               1. Set _weeks_ to _candidateWeeks_.
               1. Set _candidateWeeks_ to _candidateWeeks_ + sign.
-              1. Set _intermediate_ to BalanceISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]] + 7 × _sign_).
           1. Let _days_ be 0.
           1. Let _candidateDays_ be _sign_.
-          1. Set _intermediate_ to BalanceISODate(_constrained_.[[Year]], _constrained_.[[Month]], _constrained_.[[Day]] + 7 × _weeks_ + _candidateDays_).
-          1. Repeat, while ISODateSurpasses(_sign_, _intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]], _two_) is *false*,
+          1. Repeat, while ISODateSurpasses(_sign_, _one_, _two_, _years_, _months_, _weeks_, _candidateDays_) is *false*,
             1. Set _days_ to _candidateDays_.
             1. Set _candidateDays_ to _candidateDays_ + _sign_.
-            1. Set _intermediate_ to BalanceISODate(_intermediate_.[[Year]], _intermediate_.[[Month]], _intermediate_.[[Day]] + _sign_).
           1. Return ! CreateDateDurationRecord(_years_, _months_, _weeks_, _days_).
         1. Return NonISODateUntil(_calendar_, _one_, _two_, _largestUnit_).
       </emu-alg>

spec/plaindate.html

@@ -694,21 +694,34 @@ <h1>
       <h1>
         ISODateSurpasses (
           _sign_: -1 or 1,
-          _y1_: an integer,
-          _m1_: an integer,
-          _d1_: an integer,
+          _baseDate_: an ISO Date Record,
           _isoDate2_: an ISO Date Record,
+          _years_: an integer,
+          _months_: an integer,
+          _weeks_: an integer,
+          _days_: an integer,
         ): a Boolean
       </h1>
       <dl class="header">
         <dt>description</dt>
         <dd>
-          The return value indicates whether the date denoted by _y1_, _m1_, _d1_ surpasses that denoted by _isoDate2_ in the direction denoted by _sign_.
-          The former date does not have to exist.
+          The return value indicates whether the date _isoDate1_, the result of adding the duration denoted by _years_, _months_, _weeks_, and _days_ to _baseDate_, surpasses _isoDate2_ in the direction denoted by _sign_.
+          If _weeks_ and _days_ are both zero, then _isoDate1_ need not exist (for example, it could be February 30).
           Note that this operation is specific to date difference calculations and is not the same as CompareISODate.
         </dd>
       </dl>
       <emu-alg>
+        1. Let _yearMonth_ be BalanceISOYearMonth(_baseDate_.[[Year]] + _years_, _baseDate_.[[Month]] + _months_).
+        1. If _weeks_ is not 0 or _days_ is not 0, then
+          1. Let _regulatedDate_ be ! RegulateISODate(_yearMonth_.[[Year]], _yearMonth_.[[Month]], _baseDate_.[[Day]], ~constrain~).
+          1. Let _balancedDate_ be BalanceISODate(_regulatedDate_.[[Year]], _regulatedDate_.[[Month]], _regulatedDate_.[[Day]] + 7 * _weeks_ + _days_).
+          1. Let _y1_ be _balancedDate_.[[Year]].
+          1. Let _m1_ be _balancedDate_.[[Month]].
+          1. Let _d1_ be _balancedDate_.[[Day]].
+        1. Else,
+          1. Let _y1_ be _yearMonth_.[[Year]].
+          1. Let _m1_ be _yearMonth_.[[Month]].
+          1. Let _d1_ be _baseDate_.[[Day]].
         1. If _y1_ ≠ _isoDate2_.[[Year]], then
           1. If _sign_ × (_y1_ - _isoDate2_.[[Year]]) > 0, return *true*.
         1. Else if _m1_ ≠ _isoDate2_.[[Month]], then