/// <summary>Writes an Int32 at the end, and advance the cursor</summary>
/// <param name="writer">Target buffer</param>
/// <param name="value">Signed DWORD, 32 bits, High Endian</param>
public static void WriteInt32(ref SliceWriter writer, int value)
{
if (value <= 255)
{
if (value == 0)
{ // zero
writer.WriteByte(FdbTupleTypes.IntZero);
return;
}
if (value > 0)
{ // 1..255: frequent for array index
writer.WriteByte2(FdbTupleTypes.IntPos1, (byte)value);
return;
}
if (value > -256)
{ // -255..-1
writer.WriteByte2(FdbTupleTypes.IntNeg1, (byte)(255 + value));
return;
}
}
WriteInt64Slow(ref writer, (long)value);
}
/// <summary>Writes an UInt8 at the end, and advance the cursor</summary>
/// <param name="writer">Target buffer</param>
/// <param name="value">Unsigned BYTE, 32 bits</param>
public static void WriteInt8(ref SliceWriter writer, byte value)
{
if (value == 0)
{ // zero
writer.WriteByte(FdbTupleTypes.IntZero);
}
else
{ // 1..255: frequent for array index
writer.WriteByte2(FdbTupleTypes.IntPos1, value);
}
}
/// <summary>Writes a null value at the end, and advance the cursor</summary>
public static void WriteNil(ref SliceWriter writer)
{
writer.WriteByte(FdbTupleTypes.Nil);
}
private static unsafe bool TryWriteUnescapedUtf8String(ref SliceWriter writer, char* chars, int count)
{
Contract.Requires(chars != null && count >= 0);
// Several observations:
// * Most strings will be keywords or ASCII-only with no zeroes. These can be copied directly to the buffer
// * We will only attempt to optimze strings that don't have any 00 to escape to 00 FF. For these, we will fallback to converting to byte[] then escaping.
// * Since .NET's strings are UTF-16, the max possible UNICODE value to encode is 0xFFFF, which takes 3 bytes in UTF-8 (EF BF BF)
// * Most western europe languages have only a few non-ASCII chars here and there, and most of them will only use 2 bytes (ex: 'é' => 'C3 A9')
// * More complex scripts with dedicated symbol pages (kanjis, arabic, ....) will take 2 or 3 bytes for each charecter.
// We will first do a pass to check for the presence of 00 and non-ASCII chars
// => if we find at least on 00, we fallback to escaping the result of Encoding.UTF8.GetBytes()
// => if we find only ASCII (1..127) chars, we have an optimized path that will truncate the chars to bytes
// => if not, we will use an UTF8Encoder to convert the string to UTF-8, in chunks, using a small buffer allocated on the stack
#region First pass: look for \0 and non-ASCII chars
// fastest way to check for non-ASCII, is to OR all the chars together, and look at bits 7 to 15. If they are not all zero, there is at least ONE non-ASCII char.
// also, we abort as soon as we find a \0
char* ptr = chars;
char* end = chars + count;
char mask = '\0', c;
while (ptr < end && (c = *ptr) != '\0') { mask |= c; ++ptr; }
if (ptr < end) return false; // there is at least one \0 in the string
// bit 7-15 all unset means the string is pure ASCII
if ((mask >> 7) == 0)
{ // => directly dump the chars to the buffer
WriteUnescapedAsciiChars(ref writer, chars, count);
return true;
}
#endregion
#region Second pass: encode the string to UTF-8, in chunks
// Here we know that there is at least one unicode char, and that there are no \0
// We will tterate through the string, filling as much of the buffer as possible
bool done;
int charsUsed, bytesUsed;
int remaining = count;
ptr = chars;
// We need at most 3 * CHUNK_SIZE to encode the chunk
// > For small strings, we will allocated exactly string.Length * 3 bytes, and will be done in one chunk
// > For larger strings, we will call encoder.Convert(...) until it says it is done.
const int CHUNK_SIZE = 1024;
int bufLen = Encoding.UTF8.GetMaxByteCount(Math.Min(count, CHUNK_SIZE));
byte* buf = stackalloc byte[bufLen];
// We can not really predict the final size of the encoded string, but:
// * Western languages have a few chars that usually need 2 bytes. If we pre-allocate 50% more bytes, it should fit most of the time, without too much waste
// * Eastern langauges will have all chars encoded to 3 bytes. If we also pre-allocated 50% more, we should only need one resize of the buffer (150% x 2 = 300%), which is acceptable
writer.EnsureBytes(checked(2 + count + (count >> 1))); // preallocate 150% of the string + 2 bytes
writer.UnsafeWriteByte(FdbTupleTypes.Utf8);
var encoder = Encoding.UTF8.GetEncoder();
// note: encoder.Convert() tries to fill up the buffer as much as possible with complete chars, and will set 'done' to true when all chars have been converted.
do
{
encoder.Convert(ptr, remaining, buf, bufLen, true, out charsUsed, out bytesUsed, out done);
if (bytesUsed > 0)
{
writer.WriteBytes(buf, bytesUsed);
}
remaining -= charsUsed;
ptr += charsUsed;
}
while (!done);
Contract.Assert(remaining == 0 && ptr == end);
// close the string
writer.WriteByte(0x00);
#endregion
return true;
}
/// <summary>Writes a char array encoded in UTF-8</summary>
internal static unsafe void WriteChars(ref SliceWriter writer, char[] value, int offset, int count)
{
Contract.Requires(offset >= 0 && count >= 0);
if (count == 0)
{
if (value == null)
{ // "00"
writer.WriteByte(FdbTupleTypes.Nil);
}
else
{ // "02 00"
writer.WriteByte2(FdbTupleTypes.Utf8, 0x00);
}
}
else
{
fixed (char* chars = value)
{
if (TryWriteUnescapedUtf8String(ref writer, chars + offset, count)) return;
}
// the string contains \0 chars, we need to do it the hard way
WriteNulEscapedBytes(ref writer, FdbTupleTypes.Utf8, Encoding.UTF8.GetBytes(value, 0, count));
}
}
/// <summary>Writes a string encoded in UTF-8</summary>
public static unsafe void WriteString(ref SliceWriter writer, string value)
{
if (value == null)
{ // "00"
writer.WriteByte(FdbTupleTypes.Nil);
}
else if (value.Length == 0)
{ // "02 00"
writer.WriteByte2(FdbTupleTypes.Utf8, 0x00);
}
else
{
fixed(char* chars = value)
{
if (!TryWriteUnescapedUtf8String(ref writer, chars, value.Length))
{ // the string contains \0 chars, we need to do it the hard way
WriteNulEscapedBytes(ref writer, FdbTupleTypes.Utf8, Encoding.UTF8.GetBytes(value));
}
}
}
}
/// <summary>Writes a binary string</summary>
public static void WriteBytes(ref SliceWriter writer, byte[] value)
{
if (value == null)
{
writer.WriteByte(FdbTupleTypes.Nil);
}
else
{
WriteNulEscapedBytes(ref writer, FdbTupleTypes.Bytes, value);
}
}
/// <summary>Writes an UInt64 at the end, and advance the cursor</summary>
/// <param name="writer">Target buffer</param>
/// <param name="value">Signed QWORD, 64 bits, High Endian</param>
public static void WriteUInt64(ref SliceWriter writer, ulong value)
{
if (value <= 255)
{
if (value == 0)
{ // 0
writer.WriteByte(FdbTupleTypes.IntZero);
}
else
{ // 1..255
writer.WriteByte2(FdbTupleTypes.IntPos1, (byte)value);
}
}
else
{ // >= 256
WriteUInt64Slow(ref writer, value);
}
}