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Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

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Optimize DateTime constructors (DateToTicks and IsLeapYear) #46245

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Optimize DateToTicks and IsLeapYear
EgorBo Dec 19, 2020
69f28bf
Update DateTime.cs
EgorBo Dec 19, 2020
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8 changes: 5 additions & 3 deletions src/libraries/System.Private.CoreLib/src/System/DateTime.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -635,8 +635,8 @@ private static long DateToTicks(int year, int month, int day)
ThrowHelper.ThrowArgumentOutOfRange_BadYearMonthDay();
}

int y = year - 1;
int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
uint y = (uint)(year - 1);
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A similar optimization is part of #46245

uint n = y * 365 + y / 4 - y / 100 + y / 400 + (uint)days[month - 1] + (uint)day - 1;
return n * TicksPerDay;
}
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@EgorBo EgorBo Dec 19, 2020 •
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y is int but always is in the [1..9999] range so can be treated as unsigned (X /u C is faster than X / C) sharplab.io


Expand Down Expand Up @@ -1130,7 +1130,9 @@ public static bool IsLeapYear(int year)
{
ThrowHelper.ThrowArgumentOutOfRange_Year();
}
return (year & 3) == 0 && ((year & 15) == 0 || (year % 25) != 0);
return (year & 3) == 0 && ((year & 15) == 0 ||
// TODO: optimize "(uint)year % 25 != 0" in JIT to produce:
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Yes, we should fix the JIT instead of sprinkling manually generated magic div and mod everywhere. I had the same comment in #45479 (comment)

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ah didn't notice that pr 🙂

(year * -1030792151 > 171798691));
}
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https://godbolt.org/z/8qdPEK


// Constructs a DateTime from a string. The string must specify a
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