bxparks · bxparks · Nov 17, 2025 · Oct 23, 2025 · Oct 23, 2025 · Oct 24, 2025
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,6 +1,11 @@
 # Changelog
 
 - unreleased
+- 4.1.0 (2025-11-17, TZDB version 2025b)
+    - **Breaking** Replace `uint8_t ZonedExtra.type()` with `Resolved
+      ZonedExtra.resolved()`
+        - `ZonedExtra::resolved()` has the same behavior and semantics as
+          `ZonedDateTime.resolved()`
 - 4.0.0 (2025-10-21, TZDB version 2025b)
     - See [MIGRATING.md](MIGRATING.md) on breaking API changes, and how to
       migrate.

diff --git a/MIGRATING.md b/MIGRATING.md
@@ -2,16 +2,31 @@
 
 ## Table of Contents
 
-* [Migrating to v4.0.0](#MigratingToVersion400)
-* [Migrating to v3.0.0](#MigratingToVersion300)
-* [Migrating to v2.3.0](#MigratingToVersion220)
-* [Migrating to v2.2.0](#MigratingToVersion220)
-* [Migrating to v2.1.0](#MigratingToVersion210)
-* [Migrating to v2.0.0](#MigratingToVersion200)
-* [Migrating to v1.9.0](#MigratingToVersion190)
-* [Migrating to v1.8.0](#MigratingToVersion180)
-
-<a name="MigratingToVersion400"></a>
+* [Migrating to v4.1.0](#migrating-to-v410)
+* [Migrating to v4.0.0](#migrating-to-v400)
+* [Migrating to v3.0.0](#migrating-to-v300)
+* [Migrating to v2.3.0](#migrating-to-v230)
+* [Migrating to v2.2.0](#migrating-to-v220)
+* [Migrating to v2.1.0](#migrating-to-v210)
+* [Migrating to v2.0.0](#migrating-to-v200)
+* [Migrating to v1.9.0](#migrating-to-v190)
+* [Migrating to v1.8.0](#migrating-to-v180)
+
+## Migrating to v4.1.0
+
+The `uint8_t ZonedExtra::type()` function is replaced with `Resolved
+ZonedExtra::resolved()` which returns an enum of type `Resolved`. The new
+function has exactly the same behavior and semantics as
+`ZonedDateTime::resolved()` which simplifies the implementation and the usage of
+the library.
+
+Here is the mapping from the old values to the new enum:
+
+- `kTypeNotFound` -> `Resolved::kError`
+- `kTypeExact` -> `Resolved::kUnique`
+- `kTypeGap` -> `Resolved::kGapEarlier` or `Resolved::kGapLater`
+- `kTypeOverlap` -> `Resolved::kOverlapEarlier` or `Resolved::kOverlapLater`
+
 ## Migrating to v4.0.0
 
 These changes were originally intended for 3.0.0, but I ran out of time, so I
@@ -93,7 +108,6 @@ the `resolved` parameter which is an enum type of `Resolved`. It has 5 options:
 If the calling code does not care about how an ambiguity was resolved, then this
 parameter can be ignored.
 
-<a name="MigratingToVersion300"></a>
 ## Migrating to v3.0.0
 
 ### Info Container Class
@@ -126,7 +140,6 @@ which may have leaked out is `ace_time::internal::kAbbrevSize` which is the size
 of the string buffer needed to hold the longest TimeZone abbreviation (e.g.
 "PST"). This constant is now at `ace_time::kAbbrevSize`.
 
-<a name="MigratingToVersion230"></a>
 ## Migrating to v2.3.0
 
 The internal implementation details of various classes have changed
@@ -210,7 +223,6 @@ we can be confident that all algorithms (`BasicZoneProcessor`,
 `zonedbx`, `zonedbc`) in the AceTime library are consistent with these third
 party libraries.
 
-<a name="MigratingToVersion220"></a>
 ## Migrating to v2.2
 
 ### Immutable TimeZone class
@@ -250,10 +262,8 @@ TimeZone newTz = TimeZone::forTimeOffset(
 ZonedDateTime newDt = zdt.convertToTimeZone(newTz);
 ```
 
-<a name="MigratingToVersion210"></a>
 ## Migrating to v2.1
 
-<a name="UnifiedLinks"></a>
 ### Unified Links
 
 Over the years, I implemented 4 different versions of the Link entries:
@@ -307,7 +317,6 @@ only 2 methods which apply only to Link time zones:
     * Prints the name of the target Zone if the current zone is a link.
     * It prints nothing is `isLink()` is false.
 
-<a name="ZonedExtra"></a>
 ### ZonedExtra
 
 The `ZonedExtra` class was created to replace 3 ad-hoc query methods on the
@@ -333,10 +342,8 @@ The `ZonedExtra` object provides access to other meta-information about the time
 zone at that particular time. See the [ZonedExtra](USER_GUIDE.md#ZonedExtra)
 section in the `USER_GUIDE.md` for more detailed information about this class.
 
-<a name="MigratingToVersion200"></a>
 ## Migrating to v2.0
 
-<a name="HighLevel200"></a>
 ### High Level
 
 The primary purpose of AceTime v2 is to extend the range of years supported by
@@ -390,7 +397,6 @@ increase of 2.5-3.5 kiB of flash memory would be negligible on those processors.
 Some backwards incompatible changes were necessary from v1 to v2. These are
 explained in detail in the next section.
 
-<a name="Details200"></a>
 ### Details
 
 AceTime v2 implements the following major changes and features:
@@ -491,7 +497,6 @@ number of options:
    The next time the device is rebooted, the date and time will use the
    new epoch year instead of the old epoch year.
 
-<a name="Motivation200"></a>
 ### Background Motivation
 
 Using 32-bit integer field for epochSeconds gives a range of about 136 years.
@@ -515,13 +520,11 @@ The updated AceTime v2 is designed to support a 100-year interval from
 range needs to extended even further in the future, the "current epoch year" is
 made adjustable by the client application.
 
-<a name="MigratingToVersion190"></a>
 ## Migrating to v1.9.0
 
 The `ZoneManager` hierarchy (containing `ManualZoneManager`, `BasicZoneManager`,
 and `ExtendedZoneManager`) was refactored from v1.8.0 to v1.9.0.
 
-<a name="ConfiguringZoneManagers"></a>
 ### Configuring the Zone Managers
 
 In v1.8, the `ZoneManager` was an abstract interface class with 7 pure virtual
@@ -588,7 +591,6 @@ ExtendedoneManager zoneManager(
     zoneProcessorCache);
 ```
 
-<a name="UsingZoneManagers"></a>
 ### Using the Zone Managers
 
 In v1.8, the `ZoneManager` was the parent interface class of all polymorphic
@@ -652,7 +654,6 @@ It is assumed that most applications will hard code either the
 `BasicZoneManager` or the `ExtendedZoneManager`, and will not need this level
 of configuration.
 
-<a name="LinkManagers"></a>
 ### Link Managers
 
 In v1.8, the `LinkManager` was an interface class with pure virtual methods:
@@ -684,7 +685,6 @@ The `BasicLinkManager` and `ExtendedLinkManager` should be used directly,
 instead of through the `LinkManager` interface. Since Link Managers were
 introduced only in v1.8, I expect almost no one to be affected by this.
 
-<a name="MigratingToVersion180"></a>
 ## Migrating to v1.8.0
 
 Three breaking changes were made from v1.7.5 to v1.8.0:
@@ -708,7 +708,6 @@ Three breaking changes were made from v1.7.5 to v1.8.0:
 The following subsections show how to migrate client application from
 AceTime v1.7.5 to AceTime v1.8.0.
 
-<a name="MigratingToAceTimeClock"></a>
 ### Migrating to AceTimeClock
 
 For AceTime v1.8.0, the clock classes under the `ace_time::clock` namespace have
@@ -738,7 +737,6 @@ using namespace ace_time;
 using namespace ace_time::clock;
 ```
 
-<a name="MigratingTheDS3231Clock"></a>
 ### Migrating the DS3231Clock
 
 For AceTime v1.8.0, the `DS3231Clock` class was converted into a template class
@@ -834,7 +832,6 @@ consumption by 1500 bytes on an AVR processor. The flash consumption can be
 reduced by 2000 bytes if the "fast" version `SimpleWireFastInterface` is used
 instead.
 
-<a name="MigratingToLinkManagers"></a>
 ### Migrating to LinkManagers
 
 In v1.7.5, [thin links](USER_GUIDE.md#ThinLinks) were activated by adding the

diff --git a/README.md b/README.md
@@ -53,6 +53,18 @@ epoch of 1970-01-01 is provided through conversion functions of the `time_t`
 type. Only the 64-bit version of the `time_t` type is supported to avoid the
 [Year 2038 Problem](https://en.wikipedia.org/wiki/Year_2038_problem).
 
+The library does *not* support [leap
+seconds](https://en.wikipedia.org/wiki/Leap_second) and ignores them. Instead it
+uses [UNIX time](https://en.wikipedia.org/wiki/Unix_time) (aka POSIX time) where
+the *POSIX second* is variable in duration compared to the [SI
+second](https://en.wikipedia.org/wiki/Second). During a leap second, a POSIX
+second is conceptually equal to 2 SI seconds, and the POSIX clock changes from
+`23:59:58` to `23:59:59`, then is held for 2 seconds before rolling over to
+`00:00:00`. Most real-time clock (RTC) chips do not support leap seconds either,
+so the final `23:59:59` second will be held for only one second instead of two,
+so a clock using AceTime with such an RTC chip will be off by one second after a
+leap second compared to the atomic UTC clock.
+
 The companion library [AceTimeClock](https://github.com/bxparks/AceTimeClock)
 provides Clock classes to retrieve the time from more accurate sources, such as
 an [NTP](https://en.wikipedia.org/wiki/Network_Time_Protocol) server, or a
@@ -81,14 +93,14 @@ This library can be an alternative to the Arduino Time
 (https://github.com/JChristensen/Timezone) libraries.
 
 **Major Changes in v4.0**: Rename `LocalDate` to `PlainDate`; `LocalTime` to
-`PlainTime`; `LocalDateTime` to `PlainDateTime. Backwards compatible macros are
+`PlainTime`; `LocalDateTime` to `PlainDateTime`. Backwards compatible macros are
 provided, so most existing programs should still compile. See [Migrating to
 v4.0](MIGRATING.md#MigratingToVersion400) for more details. Add `zonedb2025` and
 `zonedbx2025` databases which contain DST transitions for year >= 2025, which
 reduces flash memory size. Replace `fold` parameter with `disambiguate` (input)
 and `resolved` (output) parameters.
 
-**Version**: 4.0.0 (2025-10-21, TZDB 2025b) \
+**Version**: 4.1.0 (2025-11-17, TZDB 2025b) \
 **Changelog**: [CHANGELOG.md](CHANGELOG.md) \
 **Migration**: [MIGRATING.md](MIGRATING.md) \
 **User Guide**: [USER_GUIDE.md](USER_GUIDE.md)
@@ -509,6 +521,7 @@ until 2200.
 - [C++11/14/17 Hinnant date](https://github.com/HowardHinnant/date) library
 - [GNU libc time](https://www.gnu.org/software/libc/libc.html) library
 - [C# Noda Time](https://nodatime.org) library
+- [Python whenever](https://pypi.org/project/whenever/)
 - [acetimec](https://github.com/bxparks/acetimec) - C version of AceTime
 - [acetimego](https://github.com/bxparks/acetimego) - Go or TinyGo version of
   AceTime

diff --git a/USER_GUIDE.md b/USER_GUIDE.md
@@ -19,7 +19,7 @@ The IANA TZ database is programmatically generated into 5 predefined databases:
 ranges, and are designed to work with different `ZoneProcessor` and
 `ZoneManager` classes.
 
-**Version**: 4.0.0 (2025-10-21, TZDB 2025b)
+**Version**: 4.1.0 (2025-11-17, TZDB 2025b)
 
 **Related Documents**:
 
@@ -1616,7 +1616,7 @@ class ZonedExtra {
         const char* abbrev);
 
     bool isError() const;
-    uint8_t type() const;
+    Resolved resolved() const;
 
     TimeOffset timeOffset() const; // stdOffset + dstOffset
     TimeOffset stdOffset() const;
@@ -1640,9 +1640,10 @@ methods on the `ZonedExtra` class:
    uint8_t hour, uint8_t minute, uint8_t second, const TimeZone& tz,
    Disambiguate disambiguate = Disambiguate::kCompatible)`
 
-Often the `ZonedDateTime` will be created first from the epochSeconds, then the
-`ZonedExtra` will be created to access additional information about the time
-zone at that particular epochSeconds (e.g. abbreviation):
+Often the `ZonedDateTime` will be created first using the `forComponents()` or
+`forEpochSeconds()` function, then the `ZonedExtra` will be created to access
+additional information about the time zone at that particular epochSeconds or
+components (e.g. abbreviation):
 
 ```C++
 ExtendedZoneProcessor zoneProcessor;
@@ -1654,9 +1655,11 @@ ZonedDateTime zdt = ZonedDateTime::forEpochSeconds(epochSeconds, tz);
 ZonedExtra ze = ZonedExtra::forEpochSeconds(epochSeconds, tz);
 ```
 
-The `ZonedExtra::type()` parameter identifies whether the given time instant
-corresponded to a DST gap, or a DST overlap, or an exact match with no
-duplicates.
+The `ZonedExtra::resolved()` parameter indicates how `forComponents()` function
+resolved a gap or an overlap according to the `disambiguate` parameter. For the
+`forEpochSeconds()` function, the resolved parameter will always be
+`Resolved::kUnique`. If the `ZonedExtra` instance is an error, then `resolved()`
+will return `Resolved::kError`.
 
 The `ZonedExtra::stdOffset()` is the standard offset of the timezone at the
 given time instant. For example, for `America/Los_Angeles` this will return
@@ -1683,10 +1686,12 @@ abbreviation is 6 characters long.
 
 The `ZonedExtra::reqStdOffset()` and `ZonedExtra::reqDstOffset()` are relevant
 and different from the corresponding `stdOffset()` and `dstOffset()` only if the
-`type()` is `kTypeGap`. This occurs only if the `ZonedExtra::forComponents()`
-factory method is used. The `reqStdOffset()` and `reqDstOffset()` are
-derived from the transition line that is used to select the earlier or later
-`PlainDateTime` instance to `epochSeconds`.
+requested `PlainDateTime` was in a gap. In other words, if the
+`ZonedExtra::resolved()` is `Resolved::kGapBefore` or `Resolved::kGapAfter`.
+This occurs only if the `ZonedExtra::forComponents()` factory method is used.
+The `reqStdOffset()` and `reqDstOffset()` are derived from the transition line
+that is used to select the earlier or later `PlainDateTime` instance to
+`epochSeconds`.
 
 The `isError()` method returns true if the given `PlainDateTime` or
 `epochSeconds` represents an error condition.
@@ -2155,10 +2160,11 @@ by JavaScript Temporal and the Python whenever libraries.
 
 #### Factory Methods with Disambiguation
 
-There are 2 main factory methods on `ZonedDateTime`: `forEpochSeconds()` and
-`forComponents()`. The `disambiguate` parameter applies to only the
-`forComponents()` method. The `forEpochSeconds()` function always corresponds to
-a unique `ZonedDateTime` object and does not need a `disambiguate` argument.
+The `ZonedDateTime` and `ZonedExtra` classes have 2 factory methods:
+`forEpochSeconds()` and `forComponents()`. The `disambiguate` parameter applies
+to only the `forComponents()` method. The `forEpochSeconds()` function always
+corresponds to a unique `ZonedDateTime` object and does not need a
+`disambiguate` argument.
 
 The `disambiguate` parameter is an enum type that takes 4 values:
 
@@ -2178,12 +2184,14 @@ then the `disambiguate` parameter has no effect, because it maps to a unique
 
 #### Resolved Disambiguation
 
-When the `forComponents()` method returns a `ZonedDateTime`, it is sometimes
-useful to know how the `disambiguate` parameter selected the result. The
-`ZonedDateTime` object exposes a `ZonedDateTime::resolved()` variable. It
-takes 5 values:
+The `ZonedDateTime::forComponents()` method and the
+`ZonedExtra::forComponents()` functions accept the `disambiguate` parameter to
+control what happens during a gap or an overlap. The resulting `ZonedDateTime`
+or `ZonedExtra` exposes a `resolved()` function that returns an enum of type
+`Resolved` which takes 6 values:
 
-- `Resolved::kUnique` - the ZonedDateTime is unique
+- `Resolved::kError` - the result was not found or an error occurred
+- `Resolved::kUnique` - the ZonedDateTime or ZonedExtra is unique
 - `Resolved::kOverlapEarlier` - the earlier time in an overlap was selected
 - `Resolved::kOverlapLater` - the later time in an overlap was selected
 - `Resolved::kGapEarlier` - the earlier time in a gap was selected

diff --git a/docs/README.md b/docs/README.md
@@ -1,7 +1,24 @@
 # Documentation
 
-* The `html` directory contains the programmatically generated
-  [Doxygen docs](https://bxparks.github.io/AceTime/html/) which are viewable on
-  GitHub Pages.
-* The other files are various subsections of the User Guide which are linked
-  from the main [README.md](../README.md).
+The main [README.md](../README.md) and [USER_GUIDE.md](../USER_GUIDE.md)
+contain the majority of the documentation.
+
+This directory contains scripts to generate [doxygen](https://www.doxygen.nl/)
+documentation from the embedded docstrings in the code.
+
+First, install doxygen and GNU Make if you don't already have them, with
+something like the following on an Ubuntu Linux machine:
+
+```
+$ sudo apt install doxygen make
+```
+
+Second, run the `make` command to generate the HTML files under the `html`
+directory:
+
+```
+$ cd docs
+$ make
+```
+
+Third, open the `./docs/html/index.html` file in your web browser.
diff --git a/docs/doxygen.cfg b/docs/doxygen.cfg
@@ -38,7 +38,7 @@ PROJECT_NAME           = AceTime
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 3.0.0
+PROJECT_NUMBER         = 4.1.0
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a

diff --git a/examples/AutoBenchmark/Benchmark.cpp b/examples/AutoBenchmark/Benchmark.cpp
@@ -127,7 +127,7 @@ void disableOptimization(uint32_t value) {
 }
 
 void disableOptimization(const ZonedExtra& extra) {
-  guard ^= extra.type() & 0xff;
+  guard ^= (uint8_t)extra.resolved() & 0xff;
   guard ^= extra.timeOffset().toMinutes() & 0xff;
   guard ^= *extra.abbrev();
 }

diff --git a/library.properties b/library.properties
@@ -1,5 +1,5 @@
 name=AceTime
-version=4.0.0
+version=4.1.0
 author=Brian T. Park <[email protected]>
 maintainer=Brian T. Park <[email protected]>
 sentence=Date, time, timezone classes for Arduino supporting the full IANA TZ Database to convert epoch seconds to date and time components in different time zones.

diff --git a/src/AceTime.h b/src/AceTime.h
@@ -77,7 +77,7 @@
 #include "zonedbc/zone_registry.h"
 
 // Version format: xxyyzz == "xx.yy.zz"
-#define ACE_TIME_VERSION 40000
-#define ACE_TIME_VERSION_STRING "4.0.0"
+#define ACE_TIME_VERSION 40100
+#define ACE_TIME_VERSION_STRING "4.1.0"
 
 #endif