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Streamline bool.TryParse/Format #64782

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merged 2 commits into from
Feb 7, 2022
Merged

Streamline bool.TryParse/Format #64782

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f34b0b2
Streamline bool.TryParse/Format
stephentoub Feb 4, 2022
1fd41cf
Factor out the failure path and add length checks
stephentoub Feb 7, 2022
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95 changes: 44 additions & 51 deletions src/libraries/System.Private.CoreLib/src/System/Boolean.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,10 @@
**
===========================================================*/

using System.Buffers.Binary;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;

namespace System
Expand Down Expand Up @@ -99,10 +101,7 @@ public bool TryFormat(Span<char> destination, out int charsWritten)
{
if ((uint)destination.Length > 3) // uint cast, per https://github.com/dotnet/runtime/issues/10596
{
destination[0] = 'T';
destination[1] = 'r';
destination[2] = 'u';
destination[3] = 'e';
BinaryPrimitives.WriteUInt64LittleEndian(MemoryMarshal.AsBytes(destination), 0x65007500720054); // "True"
charsWritten = 4;
return true;
}
Expand All @@ -111,10 +110,7 @@ public bool TryFormat(Span<char> destination, out int charsWritten)
{
if ((uint)destination.Length > 4)
{
destination[0] = 'F';
destination[1] = 'a';
destination[2] = 'l';
destination[3] = 's';
BinaryPrimitives.WriteUInt64LittleEndian(MemoryMarshal.AsBytes(destination), 0x73006C00610046); // "Fals"
destination[4] = 'e';
charsWritten = 5;
return true;
Expand Down Expand Up @@ -191,24 +187,14 @@ public int CompareTo(bool value)

// Custom string compares for early application use by config switches, etc
//
internal static bool IsTrueStringIgnoreCase(ReadOnlySpan<char> value)
{
return value.Length == 4 &&
(value[0] == 't' || value[0] == 'T') &&
(value[1] == 'r' || value[1] == 'R') &&
(value[2] == 'u' || value[2] == 'U') &&
(value[3] == 'e' || value[3] == 'E');
}
internal static bool IsTrueStringIgnoreCase(ReadOnlySpan<char> value) =>
value.Length == 4 &&
(BinaryPrimitives.ReadUInt64LittleEndian(MemoryMarshal.AsBytes(value)) | 0x0020002000200020) == 0x65007500720074; // "true" as a ulong, each char |'d with 0x0020 for case-insensitivity

internal static bool IsFalseStringIgnoreCase(ReadOnlySpan<char> value)
{
return value.Length == 5 &&
(value[0] == 'f' || value[0] == 'F') &&
(value[1] == 'a' || value[1] == 'A') &&
(value[2] == 'l' || value[2] == 'L') &&
(value[3] == 's' || value[3] == 'S') &&
(value[4] == 'e' || value[4] == 'E');
}
internal static bool IsFalseStringIgnoreCase(ReadOnlySpan<char> value) =>
value.Length == 5 &&
(((BinaryPrimitives.ReadUInt64LittleEndian(MemoryMarshal.AsBytes(value)) | 0x0020002000200020) == 0x73006C00610066) & // "fals" as a ulong, each char |'d with 0x0020 for case-insensitivity
((value[4] | 0x20) == 'e'));

// Determines whether a String represents true or false.
//
Expand All @@ -223,19 +209,18 @@ public static bool Parse(ReadOnlySpan<char> value) =>

// Determines whether a String represents true or false.
//
public static bool TryParse([NotNullWhen(true)] string? value, out bool result)
{
if (value == null)
{
result = false;
return false;
}

return TryParse(value.AsSpan(), out result);
}
public static bool TryParse([NotNullWhen(true)] string? value, out bool result) =>
TryParse(value.AsSpan(), out result);

public static bool TryParse(ReadOnlySpan<char> value, out bool result)
{
// Boolean.{Try}Parse allows for optional whitespace/null values before and
// after the case-insensitive "true"/"false", but we don't expect those to
// be the common case. We check for "true"/"false" case-insensitive in the
// fast, inlined call path, and then only if neither match do we fall back
// to trimming and making a second post-trimming attempt at matching those
// same strings.

if (IsTrueStringIgnoreCase(value))
{
result = true;
Expand All @@ -248,33 +233,41 @@ public static bool TryParse(ReadOnlySpan<char> value, out bool result)
return true;
}

// Special case: Trim whitespace as well as null characters.
value = TrimWhiteSpaceAndNull(value);
return TryParseUncommon(value, out result);

if (IsTrueStringIgnoreCase(value))
static bool TryParseUncommon(ReadOnlySpan<char> value, out bool result)
{
result = true;
return true;
}
// With "true" being 4 characters, even if we trim something from <= 4 chars,
// it can't possibly match "true" or "false".
int originalLength = value.Length;
if (originalLength >= 5)
{
value = TrimWhiteSpaceAndNull(value);
if (value.Length != originalLength)
{
// Something was trimmed. Try matching again.
if (IsTrueStringIgnoreCase(value))
{
result = true;
return true;
}

result = false;
return IsFalseStringIgnoreCase(value);
}
}

if (IsFalseStringIgnoreCase(value))
{
result = false;
return true;
return false;
}

result = false;
return false;
}

private static ReadOnlySpan<char> TrimWhiteSpaceAndNull(ReadOnlySpan<char> value)
{
const char nullChar = (char)0x0000;

int start = 0;
while (start < value.Length)
{
if (!char.IsWhiteSpace(value[start]) && value[start] != nullChar)
if (!char.IsWhiteSpace(value[start]) && value[start] != '\0')
{
break;
}
Expand All @@ -284,7 +277,7 @@ private static ReadOnlySpan<char> TrimWhiteSpaceAndNull(ReadOnlySpan<char> value
int end = value.Length - 1;
while (end >= start)
{
if (!char.IsWhiteSpace(value[end]) && value[end] != nullChar)
if (!char.IsWhiteSpace(value[end]) && value[end] != '\0')
{
break;
}
Expand Down