Optimize DateTime.Year/.DayOfYear properties; fix comments (#73277)

dotnet · Aug 6, 2022 · bf17dd6 · bf17dd6
1 parent 772444d
commit bf17dd6
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Showing 2 changed files with 41 additions and 37 deletions.
diff --git a/src/libraries/System.Private.CoreLib/src/System/DateTime.cs b/src/libraries/System.Private.CoreLib/src/System/DateTime.cs
@@ -109,9 +109,16 @@ public readonly partial struct DateTime
  // All OA dates must be less than (not <=) OADateMaxAsDouble
  private const double OADateMaxAsDouble = 2958466.0;
 
- // Euclidean Affine Functions Algorithm constants
+ // Euclidean Affine Functions Algorithm (EAF) constants
+
+ // Constants used for fast calculation of following subexpressions
+ // x / DaysPer4Years
+ // x % DaysPer4Years / 4
+ private const uint EafMultiplier = (uint)(((1UL << 32) + DaysPer4Years - 1) / DaysPer4Years); // 2,939,745
+ private const uint EafDivider = EafMultiplier * 4; // 11,758,980
+
  private const ulong TicksPer6Hours = TicksPerHour * 6;
- private const int March1BasedDayOfNewYear = 306; // Days between March 1 and January 1
+ private const int March1BasedDayOfNewYear = 306;  // Days between March 1 and January 1
 
  private static readonly uint[] s_daysToMonth365 = {
  0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
@@ -1347,13 +1354,13 @@ public DateTime Date
  // Cassio Neri, Lorenz Schneiderhttps - Euclidean Affine Functions and Applications to Calendar Algorithms - 2021
  internal void GetDate(out int year, out int month, out int day)
  {
- // y400 = number of whole 400-year periods since 3/1/0000
- // r1 = day number within 400-year period
- (uint y400, uint r1) = Math.DivRem(((uint)(UTicks / TicksPer6Hours) | 3U) + 1224, DaysPer400Years);
- ulong u2 = (ulong)Math.BigMul(2939745, (int)r1 | 3);
- ushort daySinceMarch1 = (ushort)((uint)u2 / 11758980);
+ // y100 = number of whole 100-year periods since 3/1/0000
+ // r1 = (day number within 100-year period) * 4
+ (uint y100, uint r1) = Math.DivRem(((uint)(UTicks / TicksPer6Hours) | 3U) + 1224, DaysPer400Years);
+ ulong u2 = (ulong)Math.BigMul((int)EafMultiplier, (int)r1 | 3);
+ ushort daySinceMarch1 = (ushort)((uint)u2 / EafDivider);
  int n3 = 2141 * daySinceMarch1 + 197913;
- year = (int)(100 * y400 + (uint)(u2 >> 32));
+ year = (int)(100 * y100 + (uint)(u2 >> 32));
  // compute month and day
  month = (ushort)(n3 >> 16);
  day = (ushort)n3 / 2141 + 1;
@@ -1410,10 +1417,10 @@ public int Day
  {
  get
  {
- // r1 = day number within 400-year period
+ // r1 = (day number within 100-year period) * 4
  uint r1 = (((uint)(UTicks / TicksPer6Hours) | 3U) + 1224) % DaysPer400Years;
- ulong u2 = (ulong)Math.BigMul(2939745, (int)r1 | 3);
- ushort daySinceMarch1 = (ushort)((uint)u2 / 11758980);
+ ulong u2 = (ulong)Math.BigMul((int)EafMultiplier, (int)r1 | 3);
+ ushort daySinceMarch1 = (ushort)((uint)u2 / EafDivider);
  int n3 = 2141 * daySinceMarch1 + 197913;
  // Return 1-based day-of-month
  return (ushort)n3 / 2141 + 1;
@@ -1430,22 +1437,8 @@ public int Day
  // Returns the day-of-year part of this DateTime. The returned value
  // is an integer between 1 and 366.
  //
- public int DayOfYear
- {
- get
- {
- // y400 = number of whole 400-year periods since 3/1/0000
- // r1 = day number within 400-year period
- (uint y400, uint r1) = Math.DivRem(((uint)(UTicks / TicksPer6Hours) | 3U) + 1224, DaysPer400Years);
- ulong u2 = (ulong)Math.BigMul(2939745, (int)r1 | 3);
- ushort daySinceMarch1 = (ushort)((uint)u2 / 11758980);
-
- int year = (int)(100 * y400 + (uint)(u2 >> 32)) + (daySinceMarch1 >= March1BasedDayOfNewYear ? 1 : 0);
- return daySinceMarch1 >= March1BasedDayOfNewYear // DatePartDayOfYear case
- ? daySinceMarch1 - March1BasedDayOfNewYear + 1 // rollover December 31
- : daySinceMarch1 + (366 - March1BasedDayOfNewYear) + (IsLeapYear(year) ? 1 : 0);
- }
- }
+ public int DayOfYear =>
+ 1 + (int)(((((uint)(UTicks / TicksPer6Hours) | 3U) % (uint)DaysPer400Years) | 3U) * EafMultiplier / EafDivider);
 
  // Returns the hash code for this DateTime.
  //
@@ -1501,10 +1494,10 @@ public int Month
  {
  get
  {
- // r1 = day number within 400-year period
+ // r1 = (day number within 100-year period) * 4
  uint r1 = (((uint)(UTicks / TicksPer6Hours) | 3U) + 1224) % DaysPer400Years;
- ulong u2 = (ulong)Math.BigMul(2939745, (int)r1 | 3);
- ushort daySinceMarch1 = (ushort)((uint)u2 / 11758980);
+ ulong u2 = (ulong)Math.BigMul((int)EafMultiplier, (int)r1 | 3);
+ ushort daySinceMarch1 = (ushort)((uint)u2 / EafDivider);
  int n3 = 2141 * daySinceMarch1 + 197913;
  return (ushort)(n3 >> 16) - (daySinceMarch1 >= March1BasedDayOfNewYear ? 12 : 0);
  }
@@ -1560,13 +1553,10 @@ public int Year
  {
  get
  {
- // y400 = number of whole 400-year periods since 3/1/0000
- // r1 = day number within 400-year period
- (uint y400, uint r1) = Math.DivRem(((uint)(UTicks / TicksPer6Hours) | 3U) + 1224, DaysPer400Years);
- ulong u2 = (ulong)Math.BigMul(2939745, (int)r1 | 3);
- ushort daySinceMarch1 = (ushort)((uint)u2 / 11758980);
-
- return (int)(100 * y400 + (uint)(u2 >> 32)) + (daySinceMarch1 >= March1BasedDayOfNewYear ? 1 : 0);
+ // y100 = number of whole 100-year periods since 1/1/0001
+ // r1 = (day number within 100-year period) * 4
+ (uint y100, uint r1) = Math.DivRem(((uint)(UTicks / TicksPer6Hours) | 3U), DaysPer400Years);
+ return 1 + (int)(100 * y100 + (r1 | 3) / DaysPer4Years);
  }
  }
 

diff --git a/src/libraries/System.Runtime/tests/System/DateTimeTests.cs b/src/libraries/System.Runtime/tests/System/DateTimeTests.cs
@@ -811,6 +811,20 @@ public void DayOfYear_Get_ReturnsExpected()
  Assert.Equal(170, dateTime.DayOfYear);
  }
 
+ [Fact]
+ public void DayOfYear_Random()
+ {
+ var random = new Random(2022);
+ var tries = 1000;
+ for (int i = 0; i < tries; ++i)
+ {
+ var dateTime = new DateTime(random.NextInt64(DateTime.MaxValue.Ticks));
+ var startOfYear = new DateTime(dateTime.Year, 1, 1);
+ var expectedDayOfYear = 1 + (dateTime - startOfYear).Days;
+ Assert.Equal(expectedDayOfYear, dateTime.DayOfYear);
+ }
+ }
+
  [Fact]
  public void TimeOfDay_Get_ReturnsExpected()
  {