Guard against integer overflow (swiftlang#1703)

In a recent change we changed to use integer math for better performance. However, this approach doesn't work if the date offset of the input Date cannot be represented by a Int, which would trigger a swift runtime error.

Fix this by checking if the offset is representable as an Int, and fallback to the previous implementation with floating point math if it isn't.

168600685

Author: itingliu

Sources/FoundationEssentials/Calendar/Calendar_Gregorian.swift

@@ -1994,9 +1994,6 @@ internal final class _CalendarGregorian: _CalendarProtocol, @unchecked Sendable
         let timezoneOffset = timeZone.secondsFromGMT(for: d)
         let localDate = d + Double(timezoneOffset)
 
-        let dateOffsetInSeconds = localDate.timeIntervalSinceReferenceDate.rounded(.down)
-        let date = Date(timeIntervalSinceReferenceDate: dateOffsetInSeconds) // Round down the given date to seconds
-
         let hour: Int?
         let second: Int?
         let minute: Int?
@@ -2012,13 +2009,31 @@ internal final class _CalendarGregorian: _CalendarProtocol, @unchecked Sendable
         var day: Int?
 
         let timeComponents: Calendar.ComponentSet = [.hour, .minute, .second, .nanosecond]
+        let dateOffsetInSeconds = localDate.timeIntervalSinceReferenceDate.rounded(.down)
         if !components.isDisjoint(with: timeComponents) {
-            let totalSeconds = Int(dateOffsetInSeconds)
-            let secondsInDay = (totalSeconds % 86400 + 86400) % 86400
-
-            hour = secondsInDay / 3600
-            minute = (secondsInDay % 3600) / 60
-            second = secondsInDay % 60
+            let canUseIntegerMath = dateOffsetInSeconds < Double(Int.max) && dateOffsetInSeconds >= Double(Int.min)
+            if canUseIntegerMath {
+                let totalSeconds = Int(dateOffsetInSeconds)
+                let secondsInDay = (totalSeconds % 86400 + 86400) % 86400
+                
+                let tmp: Int
+                (hour, tmp) = secondsInDay.quotientAndRemainder(dividingBy: 3600)
+                (minute, second) = tmp.quotientAndRemainder(dividingBy: 60)
+            } else {
+                var timeInDay = dateOffsetInSeconds.remainder(dividingBy: 86400) // this has precision of one second
+                if (timeInDay < 0) {
+                    timeInDay += 86400
+                }
+                
+                hour = Int(timeInDay / 3600) // zero-based
+                timeInDay = timeInDay.truncatingRemainder(dividingBy: 3600.0)
+                
+                minute = Int(timeInDay / 60)
+                timeInDay = timeInDay.truncatingRemainder(dividingBy: 60.0)
+                
+                second = Int(timeInDay)
+            }
+            
             nanosecond = Int((localDate.timeIntervalSinceReferenceDate - dateOffsetInSeconds) * 1_000_000_000)
         } else {
             hour = nil
@@ -2041,6 +2056,7 @@ internal final class _CalendarGregorian: _CalendarProtocol, @unchecked Sendable
         }
 
         do {
+            let date = Date(timeIntervalSinceReferenceDate: dateOffsetInSeconds) // Round down the given date to seconds
             let useJulianRef = useJulianReference(date)
             let julianDay = try date.julianDay()
             let julianDayYMD = Self.yearMonthDayFromJulianDay(julianDay, useJulianRef: useJulianRef)

Tests/FoundationEssentialsTests/GregorianCalendarTests.swift

@@ -583,6 +583,19 @@ private struct GregorianCalendarTests {
             testAdding(.init(month: 2), to: date2, wrap: false, expected: Date(timeIntervalSince1970: 983404800)) // 2001-03-01 00:00:00 UTC, 2001-02-28 16:00:00 PT
         }
     }
+#if _pointerBitWidth(_64)
+    @Test func testAddLargeValue() throws {
+
+        let date = Date(timeIntervalSinceReferenceDate: 656157793.922098)
+        let calendar = Calendar(identifier: .gregorian)
+        let value = 578721382704613386
+
+        let allComponents: Set<Calendar.Component> = [.era, .year, .month, .day, .hour, .minute, .second, .nanosecond, .weekday, .weekdayOrdinal, .quarter, .weekOfMonth, .weekOfYear, .yearForWeekOfYear]
+        for component in allComponents {
+            _ = calendar.date(byAdding: component, value: value, to: date)
+        }
+    }
+#endif
 
     // MARK: - Ordinality