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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
namespace System;
internal readonly partial struct Value
{
/// <summary>
/// Allows packing some <see cref="DateTimeOffset"/> values into a single <see cref="ulong"/>.
/// </summary>
private readonly struct PackedDateTimeOffset
{
// HHHHHMMT TTT...
//
// HHHHH - hour bits 1-31
// MM - minutes flag
// T - ticks bit
// 00 - :00
// 01 - :15
// 10 - :30
// 11 - :45
// Base local tick time 1800 [DateTime(1800, 1, 1).Ticks]
private const ulong BaseTicks = 567709344000000000;
private const ulong MaxTicks = BaseTicks + TickMask;
// Hours go from -14 to 14. We add 14 to get our number to store.
private const int HourOffset = 14;
private const ulong TickMask = 0b00000001_11111111_11111111_11111111__11111111_11111111_11111111_11111111;
private const ulong MinuteMask = 0b00000110_00000000_00000000_00000000__00000000_00000000_00000000_00000000;
private const ulong HourMask = 0b11111000_00000000_00000000_00000000__00000000_00000000_00000000_00000000;
private const int MinuteShift = 57;
private const int HourShift = 59;
private readonly ulong _data;
private PackedDateTimeOffset(ulong data) => _data = data;
public static bool TryCreate(DateTimeOffset dateTime, TimeSpan offset, out PackedDateTimeOffset packed)
{
bool result = false;
packed = default;
ulong ticks = (ulong)dateTime.Ticks;
if (ticks is > BaseTicks and < MaxTicks)
{
int minutes = offset.Minutes;
if (minutes % 15 == 0)
{
ulong data = (ulong)(minutes / 15) << MinuteShift;
int hours = offset.Hours + HourOffset;
// Only valid offset hours are -14 to 14
Debug.Assert(hours is >= 0 and <= 28);
data |= (ulong)hours << HourShift;
data |= ticks - BaseTicks;
packed = new(data);
result = true;
}
}
return result;
}
public DateTimeOffset Extract()
{
TimeSpan offset = new(
(int)(((_data & HourMask) >> HourShift) - HourOffset),
(int)((_data & MinuteMask) >> MinuteShift),
0);
return new((long)((_data & TickMask) + BaseTicks), offset);
}
}
}
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