AK+LibCore+Kernel: Have fewer implementations of day_of_year

The JS tests pointed out that the implementation in DateTime
had an off-by-one in the month when doing the leap year check,
so this change fixes that bug.

6 files changed, 57 insertions, 60 deletions

diff --git a/AK/Time.cpp b/AK/Time.cpp
new file mode 100644
index 0000000000..63253f90b7
--- /dev/null
+++ b/AK/Time.cpp
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2020, The SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Assertions.h>
+#include <AK/Time.h>
+
+namespace AK {
+
+int day_of_year(int year, unsigned month, int day)
+{
+    ASSERT(month >= 1 && month <= 12);
+
+    static const int seek_table[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
+    int day_of_year = seek_table[month - 1] + day - 1;
+
+    if (is_leap_year(year) && month >= 3)
+        day_of_year++;
+
+    return day_of_year;
+}
+
+}
diff --git a/AK/Time.h b/AK/Time.h
index 309218747b..612b92f691 100644
--- a/AK/Time.h
+++ b/AK/Time.h
@@ -28,6 +28,13 @@
 
 namespace AK {
 
+// Month and day start at 1. Month must be >= 1 and <= 12.
+// The return value is 0-indexed, that is Jan 1 is day 0.
+// Day may be negative or larger than the number of days
+// in the given month. If day is negative enough, the result
+// can be negative.
+int day_of_year(int year, unsigned month, int day);
+
 inline bool is_leap_year(int year)
 {
     return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
@@ -161,6 +168,7 @@ inline bool operator!=(const TimespecType& a, const TimespecType& b)
 
 }
 
+using AK::day_of_year;
 using AK::is_leap_year;
 using AK::timespec_add;
 using AK::timespec_add_timeval;
diff --git a/Kernel/CMakeLists.txt b/Kernel/CMakeLists.txt
index ff9379d823..87befd7fc2 100644
--- a/Kernel/CMakeLists.txt
+++ b/Kernel/CMakeLists.txt
@@ -207,6 +207,7 @@ set(AK_SOURCES
     ../AK/StringImpl.cpp
     ../AK/StringUtils.cpp
     ../AK/StringView.cpp
+    ../AK/Time.cpp
 )
 
 set(ELF_SOURCES
diff --git a/Kernel/RTC.cpp b/Kernel/RTC.cpp
index 25f494bd98..bced1bf661 100644
--- a/Kernel/RTC.cpp
+++ b/Kernel/RTC.cpp
@@ -49,50 +49,6 @@ static bool update_in_progress()
     return CMOS::read(0x0a) & 0x80;
 }
 
-static unsigned days_in_months_since_start_of_year(unsigned month, unsigned year)
-{
-    ASSERT(month <= 11);
-    unsigned days = 0;
-    switch (month) {
-    case 11:
-        days += 30;
-        [[fallthrough]];
-    case 10:
-        days += 31;
-        [[fallthrough]];
-    case 9:
-        days += 30;
-        [[fallthrough]];
-    case 8:
-        days += 31;
-        [[fallthrough]];
-    case 7:
-        days += 31;
-        [[fallthrough]];
-    case 6:
-        days += 30;
-        [[fallthrough]];
-    case 5:
-        days += 31;
-        [[fallthrough]];
-    case 4:
-        days += 30;
-        [[fallthrough]];
-    case 3:
-        days += 31;
-        [[fallthrough]];
-    case 2:
-        if (is_leap_year(year))
-            days += 29;
-        else
-            days += 28;
-        [[fallthrough]];
-    case 1:
-        days += 31;
-    }
-    return days;
-}
-
 static u8 bcd_to_binary(u8 bcd)
 {
     return (bcd & 0x0F) + ((bcd >> 4) * 10);
@@ -149,8 +105,7 @@ time_t now()
     ASSERT(year >= 2018);
 
     return years_to_days_since_epoch(year) * 86400
-        + days_in_months_since_start_of_year(month - 1, year) * 86400
-        + (day - 1) * 86400
+        + day_of_year(year, month, day) * 86400
         + hour * 3600
         + minute * 60
         + second;
diff --git a/Libraries/LibC/time.cpp b/Libraries/LibC/time.cpp
index 7a49ec8a95..032da5b6f0 100644
--- a/Libraries/LibC/time.cpp
+++ b/Libraries/LibC/time.cpp
@@ -117,13 +117,7 @@ static time_t tm_to_time(struct tm* tm, long timezone_adjust_seconds)
     }
 
     int days = years_to_days_since_epoch(1900 + tm->tm_year);
-
-    tm->tm_yday = tm->tm_mday - 1;
-    for (int month = 0; month < tm->tm_mon; ++month)
-        tm->tm_yday += __days_per_month[month];
-    if (tm->tm_mon > 1 && is_leap_year(1900 + tm->tm_year))
-        ++tm->tm_yday;
-
+    tm->tm_yday = day_of_year(1900 + tm->tm_year, tm->tm_mon + 1, tm->tm_mday);
     days += tm->tm_yday;
 
     int seconds = tm->tm_hour * 3600 + tm->tm_min * 60 + tm->tm_sec;
diff --git a/Libraries/LibCore/DateTime.cpp b/Libraries/LibCore/DateTime.cpp
index a1cd35cc7b..c4062699cc 100644
--- a/Libraries/LibCore/DateTime.cpp
+++ b/Libraries/LibCore/DateTime.cpp
@@ -81,13 +81,7 @@ unsigned DateTime::days_in_month() const
 
 unsigned DateTime::day_of_year() const
 {
-    static const int seek_table[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
-    int day_of_year = seek_table[m_month - 1] + m_day;
-
-    if (is_leap_year() && m_month > 3)
-        day_of_year++;
-
-    return day_of_year - 1;
+    return ::day_of_year(m_year, m_month, m_day);
 }
 
 bool DateTime::is_leap_year() const