public void TryReadTo_ForEachDesc(byte value)
{
var bts = new byte[] { 0, 1, 2, 3, 4, 5 };
var remaining = new Span <byte>(bts);
int escapeCount = 0;
for (int i = remaining.Length; i > 0 && remaining[i - 1].Equals(value); i--, escapeCount++)
{
}
var result = SpanHelpers.LastIndexNotOf(
ref MemoryMarshal.GetReference(remaining),
value,
remaining.Length);
int escapeCount1 = result != -1 ? remaining.Length - result - 1 : remaining.Length;
Assert.Equal(escapeCount, escapeCount1);
}
/// <summary>Try to read everything up to the given <paramref name="delimiter"/>, ignoring delimiters that are
/// preceded by <paramref name="delimiterEscape"/>.</summary>
/// <param name="sequence">The read data, if any.</param>
/// <param name="delimiter">The delimiter to look for.</param>
/// <param name="delimiterEscape">If found prior to <paramref name="delimiter"/> it will skip that occurrence.</param>
/// <param name="advancePastDelimiter">True to move past the <paramref name="delimiter"/> if found.</param>
/// <returns>True if the <paramref name="delimiter"/> was found.</returns>
public bool TryReadTo(out ReadOnlySequence <byte> sequence, byte delimiter, byte delimiterEscape, bool advancePastDelimiter = true)
{
ByteBufferReader copy = this;
ReadOnlySpan <byte> remaining = UnreadSpan;
bool priorEscape = false;
while (_moreData)
{
int index = SpanHelpers.IndexOf(ref MemoryMarshal.GetReference(remaining), delimiter, remaining.Length);
uint uIndex = (uint)index;
if (SharedConstants.TooBigOrNegative >= uIndex) // index != -1
{
if (0u >= uIndex && priorEscape) // index == 0
{
// We were in the escaped state, so skip this delimiter
priorEscape = false;
Advance(index + 1);
remaining = UnreadSpan;
continue;
}
else if (uIndex > 0u && remaining[index - 1] == delimiterEscape) // 此时 index 为非负值
{
// This delimiter might be skipped
// Count our escapes
var idx = SpanHelpers.LastIndexNotOf(
ref MemoryMarshal.GetReference(remaining),
delimiterEscape,
index);
int escapeCount = SharedConstants.TooBigOrNegative >= (uint)idx ? index - idx - 1 : index;
if (escapeCount == index && priorEscape)
{
// Started and ended with escape, increment once more
escapeCount++;
}
priorEscape = false;
if ((escapeCount & 1) != 0)
{
// Odd escape count means we're in the escaped state, so skip this delimiter
Advance(index + 1);
remaining = UnreadSpan;
continue;
}
}
// Found the delimiter. Move to it, slice, then move past it.
if (uIndex > 0u)
{
Advance(index);
} // 此时 index 为非负值
sequence = _sequence.Slice(copy.Position, Position);
if (advancePastDelimiter)
{
Advance(1);
}
return(true);
}
// No delimiter, need to check the end of the span for odd number of escapes then advance
{
var remainingLen = remaining.Length;
var idx = SpanHelpers.LastIndexNotOf(
ref MemoryMarshal.GetReference(remaining),
delimiterEscape,
remainingLen);
int escapeCount = SharedConstants.TooBigOrNegative >= (uint)idx ? remainingLen - idx - 1 : remainingLen;
if (priorEscape && escapeCount == remainingLen)
{
escapeCount++;
}
priorEscape = escapeCount % 2 != 0;
}
// Nothing in the current span, move to the end, checking for the skip delimiter
Advance(remaining.Length);
remaining = _currentSpan;
}
// Didn't find anything, reset our original state.
this = copy;
sequence = default;
return(false);
}
private bool TryReadToSlow(out ReadOnlySequence <byte> sequence, byte delimiter, byte delimiterEscape, int index, bool advancePastDelimiter)
{
ByteBufferReader copy = this;
ReadOnlySpan <byte> remaining = UnreadSpan;
bool priorEscape = false;
do
{
uint uIndex = (uint)index;
if (SharedConstants.TooBigOrNegative >= uIndex) // index >= 0
{
if (0u >= uIndex && priorEscape) // index == 0
{
// We were in the escaped state, so skip this delimiter
priorEscape = false;
Advance(index + 1);
remaining = UnreadSpan;
goto Continue;
}
else if (index > 0 && remaining[index - 1] == delimiterEscape)
{
// This delimiter might be skipped
// Count our escapes
int escapeCount = 1;
var idx = SpanHelpers.LastIndexNotOf(
ref MemoryMarshal.GetReference(remaining),
delimiterEscape,
index - 1);
if ((uint)idx > SharedConstants.TooBigOrNegative && priorEscape) // i < 0
{
// Started and ended with escape, increment once more
escapeCount++;
}
escapeCount += index - 2 - idx;
if ((escapeCount & 1) != 0)
{
// An odd escape count means we're currently escaped,
// skip the delimiter and reset escaped state.
Advance(index + 1);
priorEscape = false;
remaining = UnreadSpan;
goto Continue;
}
}
// Found the delimiter. Move to it, slice, then move past it.
AdvanceCurrentSpan(index);
sequence = _sequence.Slice(copy.Position, Position);
if (advancePastDelimiter)
{
Advance(1);
}
return(true);
}
else
{
// No delimiter, need to check the end of the span for odd number of escapes then advance
var remainingLen = remaining.Length;
if ((uint)remainingLen > 0u && remaining[remainingLen - 1] == delimiterEscape)
{
int escapeCount = 1;
var idx = SpanHelpers.LastIndexNotOf(
ref MemoryMarshal.GetReference(remaining),
delimiterEscape,
remainingLen - 1);
escapeCount += remainingLen - 2 - idx;
if ((uint)idx > SharedConstants.TooBigOrNegative && priorEscape) // idx < 0
{
priorEscape = 0u >= (uint)(escapeCount & 1); // equivalent to incrementing escapeCount before setting priorEscape
}
else
{
priorEscape = (escapeCount & 1) != 0;
}
}
else
{
priorEscape = false;
}
}
// Nothing in the current span, move to the end, checking for the skip delimiter
AdvanceCurrentSpan(remaining.Length);
remaining = _currentSpan;
Continue:
index = SpanHelpers.IndexOf(ref MemoryMarshal.GetReference(remaining), delimiter, remaining.Length);
} while (!End);
// Didn't find anything, reset our original state.
this = copy;
sequence = default;
return(false);
}
