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[WIP] Improve performance of Utf8Parser.TryParseInt32D #32843

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[WIP] Improve performance of Utf8Parser.TryParseInt32D #32843

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463e10b
Improve performance of Utf8Parser.TryParseInt32D
GrabYourPitchforks Feb 25, 2020
1520da4
PR feedback
GrabYourPitchforks Feb 26, 2020
b1f86ac
Further optimize switch statement
GrabYourPitchforks Feb 26, 2020
4b0d1cc
Undo unnecessary changes
GrabYourPitchforks Mar 19, 2020
c6fee52
Merge remote-tracking branch 'origin/master' into utf8tryparse_2
GrabYourPitchforks Mar 19, 2020
6ea552d
Use unsigned instead of signed indexes
GrabYourPitchforks Mar 20, 2020
2441650
Improve performance of int.Parse
GrabYourPitchforks Mar 20, 2020
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28 changes: 28 additions & 0 deletions src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Utf8Parser/ParserHelpers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,13 @@
using System.Runtime.CompilerServices;
using Internal.Runtime.CompilerServices;

#pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
#if TARGET_64BIT
using nuint = System.UInt64;
#else
using nuint = System.UInt32;
#endif

namespace System.Buffers.Text
{
internal static class ParserHelpers
Expand Down Expand Up @@ -55,6 +62,27 @@ public static bool IsDigit(int i)
return (uint)(i - '0') <= ('9' - '0');
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
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do we have to force the inlining of this method? I would assume that JIT is going to do this even without it

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BTW I've used https://godbolt.org/z/imxPHx to see if we could use some magic bit operation to get the same effect, but it looks like no ;)

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The codegen turns this into three instructions: add, cmp, jcc. I'd say that's fairly efficient. :)

public static bool TryConvertToDigit(int byteValue, out int digit)
{
digit = byteValue - '0';
return (uint)digit <= 9;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static bool TryGetDigitAt(ReadOnlySpan<byte> source, nuint index, out int digit)
{
if (source.TryGetElementAt(index, out byte tempByte) && TryConvertToDigit(tempByte, out digit))
{
return true;
}
else
{
digit = default;
return false;
}
}

//
// Enable use of ThrowHelper from TryParse() routines without introducing dozens of non-code-coveraged "value= default; bytesConsumed = 0; return false" boilerplate.
//
Expand Down
157 changes: 75 additions & 82 deletions .../System.Private.CoreLib/src/System/Buffers/Text/Utf8Parser/Utf8Parser.Integer.Signed.D.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,15 @@
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Diagnostics;

#pragma warning disable SA1121 // explicitly using type aliases instead of built-in types
#if TARGET_64BIT
using nuint = System.UInt64;
#else
using nuint = System.UInt32;
#endif

namespace System.Buffers.Text
{
public static partial class Utf8Parser
Expand Down Expand Up @@ -194,144 +203,128 @@ private static bool TryParseInt16D(ReadOnlySpan<byte> source, out short value, o

private static bool TryParseInt32D(ReadOnlySpan<byte> source, out int value, out int bytesConsumed)
{
if (source.Length < 1)
if (source.IsEmpty)
goto FalseExit;

int sign = 1;
int index = 0;
int num = source[index];
if (num == '-')
{
sign = -1;
index++;
if ((uint)index >= (uint)source.Length)
goto FalseExit;
num = source[index];
}
else if (num == '+')
{
index++;
if ((uint)index >= (uint)source.Length)
goto FalseExit;
num = source[index];
}
int sign = 0;
nuint index = 0;
int answer = source[0];

int answer = 0;
TryAgain:

if (ParserHelpers.IsDigit(num))
if (ParserHelpers.TryConvertToDigit(answer, out answer))
{
if (num == '0')
if (answer == 0)
{
do
{
index++;
if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
} while (num == '0');
if (!ParserHelpers.IsDigit(num))
goto Done;
if (!source.TryGetElementAt(index, out byte thisByte))
goto ReturnZero;
answer = thisByte;
} while (answer == '0');
if (!ParserHelpers.TryConvertToDigit(answer, out answer))
goto ReturnZero;
}

answer = num - '0';
index++;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out int num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
answer = 10 * answer + num - '0';
answer = 10 * answer + num;

// Potential overflow
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if ((uint)index >= (uint)source.Length)
goto Done;
num = source[index];
if (!ParserHelpers.IsDigit(num))
if (!ParserHelpers.TryGetDigitAt(source, index, out num))
goto Done;
index++;
if (answer > int.MaxValue / 10)
goto FalseExit; // Overflow
answer = answer * 10 + num - '0';
// if sign < 0, (-1 * sign + 1) / 2 = 1
// else, (-1 * sign + 1) / 2 = 0
if ((uint)answer > (uint)int.MaxValue + (-1 * sign + 1) / 2)
answer = answer * 10 + num;

// if sign = 0, checks answer against 0x7FFFFFFF (int.MaxValue)
// if sign = -1, checks answer against 0x80000000 (int.MinValue)
if ((uint)answer > (uint)(int.MaxValue - sign))
goto FalseExit; // Overflow

if ((uint)index >= (uint)source.Length)
goto Done;
if (!ParserHelpers.IsDigit(source[index]))

if (!ParserHelpers.TryGetDigitAt(source, index, out _))
goto Done;

// Guaranteed overflow
goto FalseExit;
}
else
{
if (answer == '-' - '0')
{
sign = -1;
}
else if (answer != '+' - '0')
{
goto FalseExit;
}

if (index != 0 || (uint)1 >= (uint)source.Length)
{
goto FalseExit;
}

answer = source[1];
index++;
goto TryAgain;
}

FalseExit:
bytesConsumed = default;
value = default;
return false;

ReturnZero:
answer = 0;

Done:
bytesConsumed = index;
value = answer * sign;
bytesConsumed = (int)index;

// If sign = 0, value = (answer ^ 0) - 0 = answer
// If sign = -1, value = (answer ^ -1) - (-1) = ~answer + 1 = -answer
Debug.Assert(sign == 0 || sign == -1);
value = (answer ^ sign) - sign;
return true;
}

Expand Down
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