[API Proposal]: Utf8Formatter/Utf8Parser should have UInt128 and Int128 overloads

[krwq]

Background and motivation

As I started looking into #73500 I realized Utf8Formatter/Utf8Parser are missing UInt128/Int128 overloads and therefore we need to unnecessarily do UTF16 <--> UTF8 conversion.

cc: @tannergooding

API Proposal

namespace System.Buffers.Text;

public static partial class Utf8Formatter
{
    public static bool TryFormat(UInt128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
    public static bool TryFormat(Int128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
}

public static partial class Utf8Parser
{
    public static bool TryParse(System.ReadOnlySpan<byte> source, out UInt128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
    public static bool TryParse(System.ReadOnlySpan<byte> source, out Int128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
}

API Usage

if (Utf8Parser.TryParse(someUtf8Span, out UInt128 value, out int bytesConsumed) && someUtf8Span.Length == bytesConsumed)
{
    Console.WriteLine($"Successfully parsed UInt128 value: {value}");
}

UInt128 value = ...;
bool result = Utf8Formatter.TryFormat(value, utf8Output, out int bytesWritten);

// and similar for Int128

Alternative Designs

No response

Risks

No response

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Issue Details

---

Background and motivation

As I started looking into #73500 I realized Utf8Formatter/Utf8Parser are missing UInt128/Int128 overloads and therefore we need to unnecessarily do UTF16 <--> UTF8 conversion.

cc: @tannergooding

API Proposal

namespace System.Buffers.Text;

public static partial class Utf8Formatter
{
    public static bool TryFormat(UInt128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
    public static bool TryFormat(Int128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
}

public static partial class Utf8Parser
{
    public static bool TryParse(System.ReadOnlySpan<byte> source, out UInt128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
    public static bool TryParse(System.ReadOnlySpan<byte> source, out Int128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
}

API Usage

if (Utf8Parser.TryParse(someUtf8Span, out UInt128 value, out int bytesConsumed) && someUtf8Span.Length == bytesConsumed)
{
    Console.WriteLine($"Successfully parsed UInt128 value: {value}");
}

UInt128 value = ...;
bool result = Utf8Formatter.TryFormat(value, utf8Output, out int bytesWritten);

// and similar for Int128

Alternative Designs

No response

Risks

No response

Author:	krwq
Assignees:	-
Labels:	api-suggestion, area-System.Buffers
Milestone:	-

[bartonjs]

Video

Looks good as proposed

namespace System.Buffers.Text;

public static partial class Utf8Formatter
{
    public static bool TryFormat(UInt128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
    public static bool TryFormat(Int128 value, System.Span<byte> destination, out int bytesWritten, System.Buffers.StandardFormat format = default(System.Buffers.StandardFormat)) { throw null; }
}

public static partial class Utf8Parser
{
    public static bool TryParse(System.ReadOnlySpan<byte> source, out UInt128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
    public static bool TryParse(System.ReadOnlySpan<byte> source, out Int128 value, out int bytesConsumed, char standardFormat = '\0') { throw null; }
}

[hrrrrustic]

@krwq @tannergooding
I'm trying to implement this API, but there are a lot of usages Convert.ChangeType and Convert.ToIntXX in the tests. Unfortunately, these methods are not support {U}Int128, is it by design or just nobody asked for this? Does this methods kind of obsolete and should be workarounded or I should create an issue with API proposal?

For Convert.ChangeType U{Int128} should implement IConvertible
For Convert.ToIntXX just add new methods

Btw, why U{Int128} returns a new instance every time in properties like {Max/Min}Value or NegativeOne? Other number types returns private consts or static readonly fields

runtime/src/libraries/System.Private.CoreLib/src/System/Int128.cs

Line 1191 in 7fdd4ee

public static Int128 MinValue => new Int128(0x8000_0000_0000_0000, 0);