/// <summary>
/// Formats a Guid as a UTF8 string.
/// </summary>
/// <param name="value">Value to format</param>
/// <param name="destination">Buffer to write the UTF8-formatted value to</param>
/// <param name="bytesWritten">Receives the length of the formatted text in bytes</param>
/// <param name="format">The standard format to use</param>
/// <returns>
/// true for success. "bytesWritten" contains the length of the formatted text in bytes.
/// false if buffer was too short. Iteratively increase the size of the buffer and retry until it succeeds.
/// </returns>
/// <remarks>
/// Formats supported:
/// D (default) nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn
/// B {nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn}
/// P (nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn)
/// N nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
/// </remarks>
/// <exceptions>
/// <cref>System.FormatException</cref> if the format is not valid for this data type.
/// </exceptions>
public static bool TryFormat(Guid value, Span <byte> destination, out int bytesWritten, StandardFormat format = default)
{
const int INSERT_DASHES = unchecked ((int)0x80000000);
const int NO_DASHES = 0;
const int INSERT_CURLY_BRACES = (CloseBrace << 16) | (OpenBrace << 8);
const int INSERT_ROUND_BRACES = (CloseParen << 16) | (OpenParen << 8);
const int NO_BRACES = 0;
const int LEN_GUID_BASE = 32;
const int LEN_ADD_DASHES = 4;
const int LEN_ADD_BRACES = 2;
// This is a 32-bit value whose contents (where 0 is the low byte) are:
// 0th byte: minimum required length of the output buffer,
// 1st byte: the ASCII byte to insert for the opening brace position (or 0 if no braces),
// 2nd byte: the ASCII byte to insert for the closing brace position (or 0 if no braces),
// 3rd byte: high bit set if dashes are to be inserted.
//
// The reason for keeping a single flag instead of separate vars is that we can avoid register spillage
// as we build up the output value.
int flags;
switch (FormattingHelpers.GetSymbolOrDefault(format, 'D'))
{
case 'D': // nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn
flags = INSERT_DASHES + NO_BRACES + LEN_GUID_BASE + LEN_ADD_DASHES;
break;
case 'B': // {nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn}
flags = INSERT_DASHES + INSERT_CURLY_BRACES + LEN_GUID_BASE + LEN_ADD_DASHES + LEN_ADD_BRACES;
break;
case 'P': // (nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn)
flags = INSERT_DASHES + INSERT_ROUND_BRACES + LEN_GUID_BASE + LEN_ADD_DASHES + LEN_ADD_BRACES;
break;
case 'N': // nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
flags = NO_BRACES + NO_DASHES + LEN_GUID_BASE;
break;
default:
return(ThrowHelper.TryFormatThrowFormatException(out bytesWritten));
}
// At this point, the low byte of flags contains the minimum required length
if ((byte)flags > destination.Length)
{
bytesWritten = 0;
return(false);
}
bytesWritten = (byte)flags;
flags >>= 8;
// At this point, the low byte of flags contains the opening brace char (if any)
if ((byte)flags != 0)
{
destination[0] = (byte)flags;
destination = destination.Slice(1);
}
flags >>= 8;
// At this point, the low byte of flags contains the closing brace char (if any)
// And since we're performing arithmetic shifting the high bit of flags is set (flags is negative) if dashes are required
DecomposedGuid guidAsBytes = default;
guidAsBytes.Guid = value;
// When a GUID is blitted, the first three components are little-endian, and the last component is big-endian.
// The line below forces the JIT to hoist the bounds check for the following segment.
// The JIT will optimize away the read, but it cannot optimize away the bounds check
// because it may have an observable side effect (throwing).
// We use 8 instead of 7 so that we also capture the dash if we're asked to insert one.
{ var unused = destination[8]; }
FormattingHelpers.WriteHexByte(guidAsBytes.Byte03, destination, 0, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte02, destination, 2, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte01, destination, 4, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte00, destination, 6, FormattingHelpers.HexCasing.Lowercase);
if (flags < 0 /* use dash? */)
{
destination[8] = Dash;
destination = destination.Slice(9);
}
else
{
destination = destination.Slice(8);
}
{ var unused = destination[4]; }
FormattingHelpers.WriteHexByte(guidAsBytes.Byte05, destination, 0, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte04, destination, 2, FormattingHelpers.HexCasing.Lowercase);
if (flags < 0 /* use dash? */)
{
destination[4] = Dash;
destination = destination.Slice(5);
}
else
{
destination = destination.Slice(4);
}
{ var unused = destination[4]; }
FormattingHelpers.WriteHexByte(guidAsBytes.Byte07, destination, 0, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte06, destination, 2, FormattingHelpers.HexCasing.Lowercase);
if (flags < 0 /* use dash? */)
{
destination[4] = Dash;
destination = destination.Slice(5);
}
else
{
destination = destination.Slice(4);
}
{ var unused = destination[4]; }
FormattingHelpers.WriteHexByte(guidAsBytes.Byte08, destination, 0, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte09, destination, 2, FormattingHelpers.HexCasing.Lowercase);
if (flags < 0 /* use dash? */)
{
destination[4] = Dash;
destination = destination.Slice(5);
}
else
{
destination = destination.Slice(4);
}
{ var unused = destination[11]; } // can't hoist bounds check on the final brace (if exists)
FormattingHelpers.WriteHexByte(guidAsBytes.Byte10, destination, 0, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte11, destination, 2, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte12, destination, 4, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte13, destination, 6, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte14, destination, 8, FormattingHelpers.HexCasing.Lowercase);
FormattingHelpers.WriteHexByte(guidAsBytes.Byte15, destination, 10, FormattingHelpers.HexCasing.Lowercase);
if ((byte)flags != 0)
{
destination[12] = (byte)flags;
}
return(true);
}