---

This section details on the original issue you should resolve

<issue_title>CharSearchValuesPolyfill._ascii should be 128 bits length</issue_title>
<issue_description>### Description

runtime/src/libraries/Common/src/System/Buffers/SearchValuesPolyfills.cs

Line 42 in be9df76

private readonly uint[] _ascii = new uint[8];

_ascii should be uint[4], otherwise this would not work:

runtime/src/libraries/Common/src/System/Buffers/SearchValuesPolyfills.cs

Line 75 in be9df76

if (offset < (uint)lookup.Length)

Reproduction Steps

I copied the source of CharSearchValuesPolyfill out to show the issue:

using System.Text;

char c = (char)200;
CharSearchValuesPolyfill searchValues = new([c]);
Console.WriteLine(searchValues.Contains(c));

class CharSearchValuesPolyfill
{
    private readonly uint[] _ascii = new uint[8];
    private readonly string _nonAscii;

    public CharSearchValuesPolyfill(ReadOnlySpan<char> values)
    {
        StringBuilder? nonAscii = null;

        foreach (char c in values)
        {
            if (c < 128)
            {
                uint offset = (uint)(c >> 5);
                uint significantBit = 1u << c;
                _ascii[offset] |= significantBit;
            }
            else
            {
                nonAscii ??= new();
                nonAscii.Append(c);
            }
        }

        _nonAscii = nonAscii?.ToString() ?? string.Empty;
    }

    public bool Contains(char value)
    {
        uint offset = (uint)(value >> 5);
        uint significantBit = 1u << value;
        uint[] lookup = _ascii;

        if (offset < (uint)lookup.Length)
        {
            return (lookup[offset] & significantBit) != 0;
        }
        else
        {
            return NonAsciiContains(value);
        }
    }

    private bool NonAsciiContains(char value)
    {
        foreach (char c in _nonAscii)
        {
            if (c == value)
            {
                return true;
            }
        }

        return false;
    }
}

Expected behavior

Prints True.

Actual behavior

Prints False.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response</issue_description>

Comments on the Issue (you are @copilot in this section)