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Add missing fast path for DateTime format "G" #129374

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Add missing fast path for DateTime format "G" #129374

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29 changes: 29 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1007,6 +1007,22 @@ internal static unsafe string Format(DateTime dateTime, string? format, IFormatP
format = dtfi.FullDateTimePattern;
break;

// For invariant DateTime ToString("G"), the expanded pattern is
// "MM/dd/yyyy HH:mm:ss" which is exactly what TryFormatInvariantG
// produces in the NullOffset case. Take the same fast path that
// ToString(InvariantCulture) (null format) already uses.
case 'G':
dtfi = DateTimeFormatInfo.GetInstance(provider);
if (offset.Ticks == NullOffset && ReferenceEquals(dtfi, DateTimeFormatInfo.InvariantInfo))
{
str = string.FastAllocateString(FormatInvariantGMinLength);
TryFormatInvariantG(dateTime, offset, new Span<char>(ref str.GetRawStringData(), str.Length), out charsWritten);
Debug.Assert(charsWritten == FormatInvariantGMinLength);
return str;
}
format = dtfi.GeneralLongTimePattern;
break;

// All other standard formats
default:
dtfi = DateTimeFormatInfo.GetInstance(provider);
Expand Down Expand Up @@ -1098,6 +1114,19 @@ internal static bool TryFormat<TChar>(DateTime dateTime, Span<TChar> destination
format = dtfi.FullDateTimePattern;
break;

// For invariant DateTime ToString("G"), the expanded pattern is
// "MM/dd/yyyy HH:mm:ss" which is exactly what TryFormatInvariantG
// produces in the NullOffset case. Take the same fast path that
// ToString(InvariantCulture) (null format) already uses.
case 'G':
dtfi = DateTimeFormatInfo.GetInstance(provider);
if (offset.Ticks == NullOffset && ReferenceEquals(dtfi, DateTimeFormatInfo.InvariantInfo))
{
return TryFormatInvariantG(dateTime, offset, destination, out charsWritten);
}
format = dtfi.GeneralLongTimePattern;
break;

// All other standard formats
default:
dtfi = DateTimeFormatInfo.GetInstance(provider);
Expand Down
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