// Returns &inputBuffer[inputLength] if the input buffer is valid.
/// <summary>
/// Given an input buffer <paramref name="pInputBuffer"/> of char length <paramref name="inputLength"/>,
/// returns a pointer to where the first invalid data appears in <paramref name="pInputBuffer"/>.
/// </summary>
/// <remarks>
/// Returns a pointer to the end of <paramref name="pInputBuffer"/> if the buffer is well-formed.
/// </remarks>
public static char *GetPointerToFirstInvalidChar(char *pInputBuffer, int inputLength, out long utf8CodeUnitCountAdjustment, out int scalarCountAdjustment)
{
Debug.Assert(inputLength >= 0, "Input length must not be negative.");
Debug.Assert(pInputBuffer != null || inputLength == 0, "Input length must be zero if input buffer pointer is null.");
// First, we'll handle the common case of all-ASCII. If this is able to
// consume the entire buffer, we'll skip the remainder of this method's logic.
int numAsciiCharsConsumedJustNow = (int)ASCIIUtility64.GetIndexOfFirstNonAsciiChar(pInputBuffer, (uint)inputLength);
Debug.Assert(0 <= numAsciiCharsConsumedJustNow && numAsciiCharsConsumedJustNow <= inputLength);
pInputBuffer += (uint)numAsciiCharsConsumedJustNow;
inputLength -= numAsciiCharsConsumedJustNow;
if (0u >= (uint)inputLength)
{
utf8CodeUnitCountAdjustment = 0;
scalarCountAdjustment = 0;
return(pInputBuffer);
}
// If we got here, it means we saw some non-ASCII data, so within our
// vectorized code paths below we'll handle all non-surrogate UTF-16
// code points branchlessly. We'll only branch if we see surrogates.
//
// We still optimistically assume the data is mostly ASCII. This means that the
// number of UTF-8 code units and the number of scalars almost matches the number
// of UTF-16 code units. As we go through the input and find non-ASCII
// characters, we'll keep track of these "adjustment" fixups. To get the
// total number of UTF-8 code units required to encode the input data, add
// the UTF-8 code unit count adjustment to the number of UTF-16 code units
// seen. To get the total number of scalars present in the input data,
// add the scalar count adjustment to the number of UTF-16 code units seen.
long tempUtf8CodeUnitCountAdjustment = 0;
int tempScalarCountAdjustment = 0;
if (Sse2.IsSupported)
{
if (inputLength >= Vector128 <ushort> .Count)
{
Vector128 <ushort> vector0080 = Vector128.Create((ushort)0x80);
Vector128 <ushort> vectorA800 = Vector128.Create((ushort)0xA800);
Vector128 <short> vector8800 = Vector128.Create(unchecked ((short)0x8800));
Vector128 <ushort> vectorZero = Vector128 <ushort> .Zero;
do
{
Vector128 <ushort> utf16Data = Sse2.LoadVector128((ushort *)pInputBuffer); // unaligned
uint mask;
// The 'charIsNonAscii' vector we're about to build will have the 0x8000 or the 0x0080
// bit set (but not both!) only if the corresponding input char is non-ASCII. Which of
// the two bits is set doesn't matter, as will be explained in the diagram a few lines
// below.
Vector128 <ushort> charIsNonAscii;
if (Sse41.IsSupported)
{
// sets 0x0080 bit if corresponding char element is >= 0x0080
charIsNonAscii = Sse41.Min(utf16Data, vector0080);
}
else
{
// sets 0x8000 bit if corresponding char element is >= 0x0080
charIsNonAscii = Sse2.AndNot(vector0080, Sse2.Subtract(vectorZero, Sse2.ShiftRightLogical(utf16Data, 7)));
}
#if DEBUG
// Quick check to ensure we didn't accidentally set both 0x8080 bits in any element.
uint debugMask = (uint)Sse2.MoveMask(charIsNonAscii.AsByte());
Debug.Assert((debugMask & (debugMask << 1)) == 0, "Two set bits shouldn't occur adjacent to each other in this mask.");
#endif // DEBUG
// sets 0x8080 bits if corresponding char element is >= 0x0800
Vector128 <ushort> charIsThreeByteUtf8Encoded = Sse2.Subtract(vectorZero, Sse2.ShiftRightLogical(utf16Data, 11));
mask = (uint)Sse2.MoveMask(Sse2.Or(charIsNonAscii, charIsThreeByteUtf8Encoded).AsByte());
// Each odd bit of mask will be 1 only if the char was >= 0x0080,
// and each even bit of mask will be 1 only if the char was >= 0x0800.
//
// Example for UTF-16 input "[ 0123 ] [ 1234 ] ...":
//
// ,-- set if char[1] is non-ASCII
// | ,-- set if char[0] is non-ASCII
// v v
// mask = ... 1 1 1 0
// ^ ^-- set if char[0] is >= 0x0800
// `-- set if char[1] is >= 0x0800
//
// (If the SSE4.1 code path is taken above, the meaning of the odd and even
// bits are swapped, but the logic below otherwise holds.)
//
// This means we can popcnt the number of set bits, and the result is the
// number of *additional* UTF-8 bytes that each UTF-16 code unit requires as
// it expands. This results in the wrong count for UTF-16 surrogate code
// units (we just counted that each individual code unit expands to 3 bytes,
// but in reality a well-formed UTF-16 surrogate pair expands to 4 bytes).
// We'll handle this in just a moment.
//
// For now, compute the popcnt but squirrel it away. We'll fold it in to the
// cumulative UTF-8 adjustment factor once we determine that there are no
// unpaired surrogates in our data. (Unpaired surrogates would invalidate
// our computed result and we'd have to throw it away.)
uint popcnt = (uint)BitOperations.PopCount(mask);
// Surrogates need to be special-cased for two reasons: (a) we need
// to account for the fact that we over-counted in the addition above;
// and (b) they require separate validation.
utf16Data = Sse2.Add(utf16Data, vectorA800);
mask = (uint)Sse2.MoveMask(Sse2.CompareLessThan(utf16Data.AsInt16(), vector8800).AsByte());
if (mask != 0)
{
// There's at least one UTF-16 surrogate code unit present.
// Since we performed a pmovmskb operation on the result of a 16-bit pcmpgtw,
// the resulting bits of 'mask' will occur in pairs:
// - 00 if the corresponding UTF-16 char was not a surrogate code unit;
// - 11 if the corresponding UTF-16 char was a surrogate code unit.
//
// A UTF-16 high/low surrogate code unit has the bit pattern [ 11011q## ######## ],
// where # is any bit; q = 0 represents a high surrogate, and q = 1 represents
// a low surrogate. Since we added 0xA800 in the vectorized operation above,
// our surrogate pairs will now have the bit pattern [ 10000q## ######## ].
// If we logical right-shift each word by 3, we'll end up with the bit pattern
// [ 00010000 q####### ], which means that we can immediately use pmovmskb to
// determine whether a given char was a high or a low surrogate.
//
// Therefore the resulting bits of 'mask2' will occur in pairs:
// - 00 if the corresponding UTF-16 char was a high surrogate code unit;
// - 01 if the corresponding UTF-16 char was a low surrogate code unit;
// - ## (garbage) if the corresponding UTF-16 char was not a surrogate code unit.
// Since 'mask' already has 00 in these positions (since the corresponding char
// wasn't a surrogate), "mask AND mask2 == 00" holds for these positions.
uint mask2 = (uint)Sse2.MoveMask(Sse2.ShiftRightLogical(utf16Data, 3).AsByte());
// 'lowSurrogatesMask' has its bits occur in pairs:
// - 01 if the corresponding char was a low surrogate char,
// - 00 if the corresponding char was a high surrogate char or not a surrogate at all.
uint lowSurrogatesMask = mask2 & mask;
// 'highSurrogatesMask' has its bits occur in pairs:
// - 01 if the corresponding char was a high surrogate char,
// - 00 if the corresponding char was a low surrogate char or not a surrogate at all.
uint highSurrogatesMask = (mask2 ^ 0b_0101_0101_0101_0101u /* flip all even-numbered bits 00 <-> 01 */) & mask;
Debug.Assert((highSurrogatesMask & lowSurrogatesMask) == 0,
"A char cannot simultaneously be both a high and a low surrogate char.");
Debug.Assert(((highSurrogatesMask | lowSurrogatesMask) & 0b_1010_1010_1010_1010u) == 0,
"Only even bits (no odd bits) of the masks should be set.");
// Now check that each high surrogate is followed by a low surrogate and that each
// low surrogate follows a high surrogate. We make an exception for the case where
// the final char of the vector is a high surrogate, since we can't perform validation
// on it until the next iteration of the loop when we hope to consume the matching
// low surrogate.
highSurrogatesMask <<= 2;
if ((ushort)highSurrogatesMask != lowSurrogatesMask)
{
goto NonVectorizedLoop; // error: mismatched surrogate pair; break out of vectorized logic
}
if (highSurrogatesMask > ushort.MaxValue)
{
// There was a standalone high surrogate at the end of the vector.
// We'll adjust our counters so that we don't consider this char consumed.
highSurrogatesMask = (ushort)highSurrogatesMask; // don't allow stray high surrogate to be consumed by popcnt
popcnt -= 2; // the '0xC000_0000' bits in the original mask are shifted out and discarded, so account for that here
pInputBuffer--;
inputLength++;
}
// If we're 64-bit, we can perform the zero-extension of the surrogate pairs count for
// free right now, saving the extension step a few lines below. If we're 32-bit, the
// convertion to nuint immediately below is a no-op, and we'll pay the cost of the real
// 64 -bit extension a few lines below.
nuint surrogatePairsCountNuint = (uint)BitOperations.PopCount(highSurrogatesMask);
// 2 UTF-16 chars become 1 Unicode scalar
tempScalarCountAdjustment -= (int)surrogatePairsCountNuint;
// Since each surrogate code unit was >= 0x0800, we eagerly assumed
// it'd be encoded as 3 UTF-8 code units, so our earlier popcnt computation
// assumes that the pair is encoded as 6 UTF-8 code units. Since each
// pair is in reality only encoded as 4 UTF-8 code units, we need to
// perform this adjustment now.
if (PlatformDependent.Is64BitProcess)
{
// Since we've already zero-extended surrogatePairsCountNuint, we can directly
// sub + sub. It's more efficient than shl + sub.
tempUtf8CodeUnitCountAdjustment -= (long)surrogatePairsCountNuint;
tempUtf8CodeUnitCountAdjustment -= (long)surrogatePairsCountNuint;
}
else
{
// Take the hit of the 64-bit extension now.
tempUtf8CodeUnitCountAdjustment -= 2 * (uint)surrogatePairsCountNuint;
}
}
tempUtf8CodeUnitCountAdjustment += popcnt;
pInputBuffer += Vector128 <ushort> .Count;
inputLength -= Vector128 <ushort> .Count;
} while (inputLength >= Vector128 <ushort> .Count);
}
}
else if (Vector.IsHardwareAccelerated)
{
if (inputLength >= Vector <ushort> .Count)
{
Vector <ushort> vector0080 = new Vector <ushort>(0x0080);
Vector <ushort> vector0400 = new Vector <ushort>(0x0400);
Vector <ushort> vector0800 = new Vector <ushort>(0x0800);
Vector <ushort> vectorD800 = new Vector <ushort>(0xD800);
do
{
// The 'twoOrMoreUtf8Bytes' and 'threeOrMoreUtf8Bytes' vectors will contain
// elements whose values are 0xFFFF (-1 as signed word) iff the corresponding
// UTF-16 code unit was >= 0x0080 and >= 0x0800, respectively. By summing these
// vectors, each element of the sum will contain one of three values:
//
// 0x0000 ( 0) = original char was 0000..007F
// 0xFFFF (-1) = original char was 0080..07FF
// 0xFFFE (-2) = original char was 0800..FFFF
//
// We'll negate them to produce a value 0..2 for each element, then sum all the
// elements together to produce the number of *additional* UTF-8 code units
// required to represent this UTF-16 data. This is similar to the popcnt step
// performed by the SSE2 code path. This will overcount surrogates, but we'll
// handle that shortly.
Vector <ushort> utf16Data = Unsafe.ReadUnaligned <Vector <ushort> >(pInputBuffer);
Vector <ushort> twoOrMoreUtf8Bytes = Vector.GreaterThanOrEqual(utf16Data, vector0080);
Vector <ushort> threeOrMoreUtf8Bytes = Vector.GreaterThanOrEqual(utf16Data, vector0800);
Vector <nuint> sumVector = (Vector <nuint>)(Vector <ushort> .Zero - twoOrMoreUtf8Bytes - threeOrMoreUtf8Bytes);
// We'll try summing by a natural word (rather than a 16-bit word) at a time,
// which should halve the number of operations we must perform.
nuint popcnt = 0;
for (int i = 0; i < Vector <nuint> .Count; i++)
{
popcnt += sumVector[i];
}
uint popcnt32 = (uint)popcnt;
if (PlatformDependent.Is64BitProcess)
{
popcnt32 += (uint)(popcnt >> 32);
}
// As in the SSE4.1 paths, compute popcnt but don't fold it in until we
// know there aren't any unpaired surrogates in the input data.
popcnt32 = (ushort)popcnt32 + (popcnt32 >> 16);
// Now check for surrogates.
utf16Data -= vectorD800;
Vector <ushort> surrogateChars = Vector.LessThan(utf16Data, vector0800);
if (surrogateChars != Vector <ushort> .Zero)
{
// There's at least one surrogate (high or low) UTF-16 code unit in
// the vector. We'll build up additional vectors: 'highSurrogateChars'
// and 'lowSurrogateChars', where the elements are 0xFFFF iff the original
// UTF-16 code unit was a high or low surrogate, respectively.
Vector <ushort> highSurrogateChars = Vector.LessThan(utf16Data, vector0400);
Vector <ushort> lowSurrogateChars = Vector.AndNot(surrogateChars, highSurrogateChars);
// We want to make sure that each high surrogate code unit is followed by
// a low surrogate code unit and each low surrogate code unit follows a
// high surrogate code unit. Since we don't have an equivalent of pmovmskb
// or palignr available to us, we'll do this as a loop. We won't look at
// the very last high surrogate char element since we don't yet know if
// the next vector read will have a low surrogate char element.
if (lowSurrogateChars[0] != 0)
{
goto Error; // error: start of buffer contains standalone low surrogate char
}
ushort surrogatePairsCount = 0;
for (int i = 0; i < Vector <ushort> .Count - 1; i++)
{
surrogatePairsCount -= highSurrogateChars[i]; // turns into +1 or +0
if (highSurrogateChars[i] != lowSurrogateChars[i + 1])
{
goto NonVectorizedLoop; // error: mismatched surrogate pair; break out of vectorized logic
}
}
if (highSurrogateChars[Vector <ushort> .Count - 1] != 0)
{
// There was a standalone high surrogate at the end of the vector.
// We'll adjust our counters so that we don't consider this char consumed.
pInputBuffer--;
inputLength++;
popcnt32 -= 2;
}
nint surrogatePairsCountNint = (nint)surrogatePairsCount; // zero-extend to native int size
// 2 UTF-16 chars become 1 Unicode scalar
tempScalarCountAdjustment -= (int)surrogatePairsCountNint;
// Since each surrogate code unit was >= 0x0800, we eagerly assumed
// it'd be encoded as 3 UTF-8 code units. Each surrogate half is only
// encoded as 2 UTF-8 code units (for 4 UTF-8 code units total),
// so we'll adjust this now.
tempUtf8CodeUnitCountAdjustment -= surrogatePairsCountNint;
tempUtf8CodeUnitCountAdjustment -= surrogatePairsCountNint;
}
tempUtf8CodeUnitCountAdjustment += popcnt32;
pInputBuffer += Vector <ushort> .Count;
inputLength -= Vector <ushort> .Count;
} while (inputLength >= Vector <ushort> .Count);
}
}
NonVectorizedLoop:
// Vectorization isn't supported on our current platform, or the input was too small to benefit
// from vectorization, or we saw invalid UTF-16 data in the vectorized code paths and need to
// drain remaining valid chars before we report failure.
for (; inputLength > 0; pInputBuffer++, inputLength--)
{
uint thisChar = pInputBuffer[0];
if (thisChar <= 0x7F)
{
continue;
}
// Bump adjustment by +1 for U+0080..U+07FF; by +2 for U+0800..U+FFFF.
// This optimistically assumes no surrogates, which we'll handle shortly.
tempUtf8CodeUnitCountAdjustment += (thisChar + 0x0001_F800u) >> 16;
if (!UnicodeUtility.IsSurrogateCodePoint(thisChar))
{
continue;
}
// Found a surrogate char. Back out the adjustment we made above, then
// try to consume the entire surrogate pair all at once. We won't bother
// trying to interpret the surrogate pair as a scalar value; we'll only
// validate that its bit pattern matches what's expected for a surrogate pair.
tempUtf8CodeUnitCountAdjustment -= 2;
if (inputLength == 1)
{
goto Error; // input buffer too small to read a surrogate pair
}
thisChar = Unsafe.ReadUnaligned <uint>(pInputBuffer);
if (((thisChar - (BitConverter.IsLittleEndian ? 0xDC00_D800u : 0xD800_DC00u)) & 0xFC00_FC00u) != 0)
{
goto Error; // not a well-formed surrogate pair
}
tempScalarCountAdjustment--; // 2 UTF-16 code units -> 1 scalar
tempUtf8CodeUnitCountAdjustment += 2; // 2 UTF-16 code units -> 4 UTF-8 code units
pInputBuffer++; // consumed one extra char
inputLength--;
}
Error:
// Also used for normal return.
utf8CodeUnitCountAdjustment = tempUtf8CodeUnitCountAdjustment;
scalarCountAdjustment = tempScalarCountAdjustment;
return(pInputBuffer);
}
// Returns &inputBuffer[inputLength] if the input buffer is valid.
/// <summary>
/// Given an input buffer <paramref name="pInputBuffer"/> of byte length <paramref name="inputLength"/>,
/// returns a pointer to where the first invalid data appears in <paramref name="pInputBuffer"/>.
/// </summary>
/// <remarks>
/// Returns a pointer to the end of <paramref name="pInputBuffer"/> if the buffer is well-formed.
/// </remarks>
public static byte *GetPointerToFirstInvalidByte(byte *pInputBuffer, int inputLength, out int utf16CodeUnitCountAdjustment, out int scalarCountAdjustment)
{
Debug.Assert(inputLength >= 0, "Input length must not be negative.");
Debug.Assert(pInputBuffer != null || inputLength == 0, "Input length must be zero if input buffer pointer is null.");
// First, try to drain off as many ASCII bytes as we can from the beginning.
{
nuint numAsciiBytesCounted = ASCIIUtility64.GetIndexOfFirstNonAsciiByte(pInputBuffer, (uint)inputLength);
pInputBuffer += numAsciiBytesCounted;
// Quick check - did we just end up consuming the entire input buffer?
// If so, short-circuit the remainder of the method.
inputLength -= (int)numAsciiBytesCounted;
if (0u >= inputLength)
{
utf16CodeUnitCountAdjustment = 0;
scalarCountAdjustment = 0;
return(pInputBuffer);
}
}
#if DEBUG
// Keep these around for final validation at the end of the method.
byte *pOriginalInputBuffer = pInputBuffer;
int originalInputLength = inputLength;
#endif
// Enregistered locals that we'll eventually out to our caller.
int tempUtf16CodeUnitCountAdjustment = 0;
int tempScalarCountAdjustment = 0;
if (inputLength < sizeof(uint))
{
goto ProcessInputOfLessThanDWordSize;
}
byte *pFinalPosWhereCanReadDWordFromInputBuffer = pInputBuffer + (uint)inputLength - sizeof(uint);
// Begin the main loop.
#if DEBUG
byte *pLastBufferPosProcessed = null; // used for invariant checking in debug builds
#endif
while (pInputBuffer <= pFinalPosWhereCanReadDWordFromInputBuffer)
{
// Read 32 bits at a time. This is enough to hold any possible UTF8-encoded scalar.
uint thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
AfterReadDWord:
#if DEBUG
Debug.Assert(pLastBufferPosProcessed < pInputBuffer, "Algorithm should've made forward progress since last read.");
pLastBufferPosProcessed = pInputBuffer;
#endif
// First, check for the common case of all-ASCII bytes.
if (ASCIIUtility.AllBytesInUInt32AreAscii(thisDWord))
{
// We read an all-ASCII sequence.
pInputBuffer += sizeof(uint);
// If we saw a sequence of all ASCII, there's a good chance a significant amount of following data is also ASCII.
// Below is basically unrolled loops with poor man's vectorization.
// Below check is "can I read at least five DWORDs from the input stream?"
// n.b. Since we incremented pInputBuffer above the below subtraction may result in a negative value,
// hence using nint instead of nuint.
if ((nint)(void *)Unsafe.ByteOffset(ref *pInputBuffer, ref *pFinalPosWhereCanReadDWordFromInputBuffer) >= 4 * sizeof(uint))
{
// We want reads in the inner loop to be aligned. So let's perform a quick
// ASCII check of the next 32 bits (4 bytes) now, and if that succeeds bump
// the read pointer up to the next aligned address.
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
if (!ASCIIUtility.AllBytesInUInt32AreAscii(thisDWord))
{
goto AfterReadDWordSkipAllBytesAsciiCheck;
}
pInputBuffer = (byte *)((nuint)(pInputBuffer + 4) & ~(nuint)3);
// At this point, the input buffer offset points to an aligned DWORD. We also know that there's
// enough room to read at least four DWORDs from the buffer. (Heed the comment a few lines above:
// the original 'if' check confirmed that there were 5 DWORDs before the alignment check, and
// the alignment check consumes at most a single DWORD.)
byte *pInputBufferFinalPosAtWhichCanSafelyLoop = pFinalPosWhereCanReadDWordFromInputBuffer - 3 * sizeof(uint); // can safely read 4 DWORDs here
uint mask;
do
{
if (Sse2.IsSupported && Bmi1.IsSupported)
{
// pInputBuffer is 32-bit aligned but not necessary 128-bit aligned, so we're
// going to perform an unaligned load. We don't necessarily care about aligning
// this because we pessimistically assume we'll encounter non-ASCII data at some
// point in the not-too-distant future (otherwise we would've stayed entirely
// within the all-ASCII vectorized code at the entry to this method).
mask = (uint)Sse2.MoveMask(Sse2.LoadVector128((byte *)pInputBuffer));
if (mask != 0)
{
goto Sse2LoopTerminatedEarlyDueToNonAsciiData;
}
}
else
{
if (!ASCIIUtility.AllBytesInUInt32AreAscii(((uint *)pInputBuffer)[0] | ((uint *)pInputBuffer)[1]))
{
goto LoopTerminatedEarlyDueToNonAsciiDataInFirstPair;
}
if (!ASCIIUtility.AllBytesInUInt32AreAscii(((uint *)pInputBuffer)[2] | ((uint *)pInputBuffer)[3]))
{
goto LoopTerminatedEarlyDueToNonAsciiDataInSecondPair;
}
}
pInputBuffer += 4 * sizeof(uint); // consumed 4 DWORDs
} while (pInputBuffer <= pInputBufferFinalPosAtWhichCanSafelyLoop);
continue; // need to perform a bounds check because we might be running out of data
Sse2LoopTerminatedEarlyDueToNonAsciiData:
Debug.Assert(BitConverter.IsLittleEndian);
Debug.Assert(Sse2.IsSupported);
Debug.Assert(Bmi1.IsSupported);
// The 'mask' value will have a 0 bit for each ASCII byte we saw and a 1 bit
// for each non-ASCII byte we saw. We can count the number of ASCII bytes,
// bump our input counter by that amount, and resume processing from the
// "the first byte is no longer ASCII" portion of the main loop.
Debug.Assert(mask != 0);
pInputBuffer += Bmi1.TrailingZeroCount(mask);
if (pInputBuffer > pFinalPosWhereCanReadDWordFromInputBuffer)
{
goto ProcessRemainingBytesSlow;
}
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer); // no longer guaranteed to be aligned
goto BeforeProcessTwoByteSequence;
LoopTerminatedEarlyDueToNonAsciiDataInSecondPair:
pInputBuffer += 2 * sizeof(uint); // consumed 2 DWORDs
LoopTerminatedEarlyDueToNonAsciiDataInFirstPair:
// We know that there's *at least* two DWORDs of data remaining in the buffer.
// We also know that one of them (or both of them) contains non-ASCII data somewhere.
// Let's perform a quick check here to bypass the logic at the beginning of the main loop.
thisDWord = *(uint *)pInputBuffer; // still aligned here
if (ASCIIUtility.AllBytesInUInt32AreAscii(thisDWord))
{
pInputBuffer += sizeof(uint); // consumed 1 more DWORD
thisDWord = *(uint *)pInputBuffer; // still aligned here
}
goto AfterReadDWordSkipAllBytesAsciiCheck;
}
continue; // not enough data remaining to unroll loop - go back to beginning with bounds checks
}
AfterReadDWordSkipAllBytesAsciiCheck:
Debug.Assert(!ASCIIUtility.AllBytesInUInt32AreAscii(thisDWord)); // this should have been handled earlier
// Next, try stripping off ASCII bytes one at a time.
// We only handle up to three ASCII bytes here since we handled the four ASCII byte case above.
{
uint numLeadingAsciiBytes = ASCIIUtility.CountNumberOfLeadingAsciiBytesFromUInt32WithSomeNonAsciiData(thisDWord);
pInputBuffer += numLeadingAsciiBytes;
if (pFinalPosWhereCanReadDWordFromInputBuffer < pInputBuffer)
{
goto ProcessRemainingBytesSlow; // Input buffer doesn't contain enough data to read a DWORD
}
else
{
// The input buffer at the current offset contains a non-ASCII byte.
// Read an entire DWORD and fall through to multi-byte consumption logic.
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
}
}
BeforeProcessTwoByteSequence:
// At this point, we suspect we're working with a multi-byte code unit sequence,
// but we haven't yet validated it for well-formedness.
// The masks and comparands are derived from the Unicode Standard, Table 3-6.
// Additionally, we need to check for valid byte sequences per Table 3-7.
// Check the 2-byte case.
thisDWord -= (BitConverter.IsLittleEndian) ? 0x0000_80C0u : 0xC080_0000u;
if (0u >= (thisDWord & (BitConverter.IsLittleEndian ? 0x0000_C0E0u : 0xE0C0_0000u)))
{
// Per Table 3-7, valid sequences are:
// [ C2..DF ] [ 80..BF ]
//
// Due to our modification of 'thisDWord' above, this becomes:
// [ 02..1F ] [ 00..3F ]
//
// We've already checked that the leading byte was originally in the range [ C0..DF ]
// and that the trailing byte was originally in the range [ 80..BF ], so now we only need
// to check that the modified leading byte is >= [ 02 ].
if ((BitConverter.IsLittleEndian && (byte)thisDWord < 0x02u) ||
(!BitConverter.IsLittleEndian && thisDWord < 0x0200_0000u))
{
goto Error; // overlong form - leading byte was [ C0 ] or [ C1 ]
}
ProcessTwoByteSequenceSkipOverlongFormCheck:
// Optimization: If this is a two-byte-per-character language like Cyrillic or Hebrew,
// there's a good chance that if we see one two-byte run then there's another two-byte
// run immediately after. Let's check that now.
// On little-endian platforms, we can check for the two-byte UTF8 mask *and* validate that
// the value isn't overlong using a single comparison. On big-endian platforms, we'll need
// to validate the mask and validate that the sequence isn't overlong as two separate comparisons.
if ((BitConverter.IsLittleEndian && Utf8Utility.UInt32EndsWithValidUtf8TwoByteSequenceLittleEndian(thisDWord)) ||
(!BitConverter.IsLittleEndian && (Utf8Utility.UInt32EndsWithUtf8TwoByteMask(thisDWord) && !Utf8Utility.UInt32EndsWithOverlongUtf8TwoByteSequence(thisDWord))))
{
// We have two runs of two bytes each.
pInputBuffer += 4;
tempUtf16CodeUnitCountAdjustment -= 2; // 4 UTF-8 code units -> 2 UTF-16 code units (and 2 scalars)
if (pInputBuffer <= pFinalPosWhereCanReadDWordFromInputBuffer)
{
// Optimization: If we read a long run of two-byte sequences, the next sequence is probably
// also two bytes. Check for that first before going back to the beginning of the loop.
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
if (BitConverter.IsLittleEndian)
{
if (Utf8Utility.UInt32BeginsWithValidUtf8TwoByteSequenceLittleEndian(thisDWord))
{
// The next sequence is a valid two-byte sequence.
goto ProcessTwoByteSequenceSkipOverlongFormCheck;
}
}
else
{
if (Utf8Utility.UInt32BeginsWithUtf8TwoByteMask(thisDWord))
{
if (Utf8Utility.UInt32BeginsWithOverlongUtf8TwoByteSequence(thisDWord))
{
goto Error; // The next sequence purports to be a 2-byte sequence but is overlong.
}
goto ProcessTwoByteSequenceSkipOverlongFormCheck;
}
}
// If we reached this point, the next sequence is something other than a valid
// two-byte sequence, so go back to the beginning of the loop.
goto AfterReadDWord;
}
else
{
goto ProcessRemainingBytesSlow; // Running out of data - go down slow path
}
}
// The buffer contains a 2-byte sequence followed by 2 bytes that aren't a 2-byte sequence.
// Unlikely that a 3-byte sequence would follow a 2-byte sequence, so perhaps remaining
// bytes are ASCII?
tempUtf16CodeUnitCountAdjustment--; // 2-byte sequence + (some number of ASCII bytes) -> 1 UTF-16 code units (and 1 scalar) [+ trailing]
if (Utf8Utility.UInt32ThirdByteIsAscii(thisDWord))
{
if (Utf8Utility.UInt32FourthByteIsAscii(thisDWord))
{
pInputBuffer += 4;
}
else
{
pInputBuffer += 3;
// A two-byte sequence followed by an ASCII byte followed by a non-ASCII byte.
// Read in the next DWORD and jump directly to the start of the multi-byte processing block.
if (pInputBuffer <= pFinalPosWhereCanReadDWordFromInputBuffer)
{
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
goto BeforeProcessTwoByteSequence;
}
}
}
else
{
pInputBuffer += 2;
}
continue;
}
// Check the 3-byte case.
// We need to restore the C0 leading byte we stripped out earlier, then we can strip out the expected E0 byte.
thisDWord -= (BitConverter.IsLittleEndian) ? (0x0080_00E0u - 0x0000_00C0u) : (0xE000_8000u - 0xC000_0000u);
if (0u >= (thisDWord & (BitConverter.IsLittleEndian ? 0x00C0_C0F0u : 0xF0C0_C000u)))
{
ProcessThreeByteSequenceWithCheck:
// We assume the caller has confirmed that the bit pattern is representative of a three-byte
// sequence, but it may still be overlong or surrogate. We need to check for these possibilities.
//
// Per Table 3-7, valid sequences are:
// [ E0 ] [ A0..BF ] [ 80..BF ]
// [ E1..EC ] [ 80..BF ] [ 80..BF ]
// [ ED ] [ 80..9F ] [ 80..BF ]
// [ EE..EF ] [ 80..BF ] [ 80..BF ]
//
// Big-endian examples of using the above validation table:
// E0A0 = 1110 0000 1010 0000 => invalid (overlong ) patterns are 1110 0000 100# ####
// ED9F = 1110 1101 1001 1111 => invalid (surrogate) patterns are 1110 1101 101# ####
// If using the bitmask ......................................... 0000 1111 0010 0000 (=0F20),
// Then invalid (overlong) patterns match the comparand ......... 0000 0000 0000 0000 (=0000),
// And invalid (surrogate) patterns match the comparand ......... 0000 1101 0010 0000 (=0D20).
//
// It's ok if the caller has manipulated 'thisDWord' (e.g., by subtracting 0xE0 or 0x80)
// as long as they haven't touched the bits we're about to use in our mask checking below.
if (BitConverter.IsLittleEndian)
{
// The "overlong or surrogate" check can be implemented using a single jump, but there's
// some overhead to moving the bits into the correct locations in order to perform the
// correct comparison, and in practice the processor's branch prediction capability is
// good enough that we shouldn't bother. So we'll use two jumps instead.
// Can't extract this check into its own helper method because JITter produces suboptimal
// assembly, even with aggressive inlining.
// Code below becomes 5 instructions: test, jz, lea, test, jz
if ((0u >= (thisDWord & 0x0000_200Fu)) || (0u >= ((thisDWord - 0x0000_200Du) & 0x0000_200Fu)))
{
goto Error; // overlong or surrogate
}
}
else
{
if ((0u >= (thisDWord & 0x0F20_0000u)) || (0u >= ((thisDWord - 0x0D20_0000u) & 0x0F20_0000u)))
{
goto Error; // overlong or surrogate
}
}
ProcessSingleThreeByteSequenceSkipOverlongAndSurrogateChecks:
// Occasionally one-off ASCII characters like spaces, periods, or newlines will make their way
// in to the text. If this happens strip it off now before seeing if the next character
// consists of three code units.
// Branchless: consume a 3-byte UTF-8 sequence and optionally an extra ASCII byte hanging off the end
nint asciiAdjustment;
if (BitConverter.IsLittleEndian)
{
asciiAdjustment = (int)thisDWord >> 31; // smear most significant bit across entire value
}
else
{
asciiAdjustment = (nint)(sbyte)thisDWord >> 7; // smear most significant bit of least significant byte across entire value
}
// asciiAdjustment = 0 if fourth byte is ASCII; -1 otherwise
// Please *DO NOT* reorder the below two lines. It provides extra defense in depth in case this method
// is ever changed such that pInputBuffer becomes a 'ref byte' instead of a simple 'byte*'. It's valid
// to add 4 before backing up since we already checked previously that the input buffer contains at
// least a DWORD's worth of data, so we're not going to run past the end of the buffer where the GC can
// no longer track the reference. However, we can't back up before adding 4, since we might back up to
// before the start of the buffer, and the GC isn't guaranteed to be able to track this.
pInputBuffer += 4; // optimistically, assume consumed a 3-byte UTF-8 sequence plus an extra ASCII byte
pInputBuffer += asciiAdjustment; // back up if we didn't actually consume an ASCII byte
tempUtf16CodeUnitCountAdjustment -= 2; // 3 (or 4) UTF-8 bytes -> 1 (or 2) UTF-16 code unit (and 1 [or 2] scalar)
SuccessfullyProcessedThreeByteSequence:
if (PlatformDependent.Is64BitProcess && BitConverter.IsLittleEndian)
{
// x64 little-endian optimization: A three-byte character could indicate CJK text,
// which makes it likely that the character following this one is also CJK.
// We'll try to process several three-byte sequences at a time.
// The check below is really "can we read 9 bytes from the input buffer?" since 'pFinalPos...' is already offset
// n.b. The subtraction below could result in a negative value (since we advanced pInputBuffer above), so
// use nint instead of nuint.
if ((nint)(pFinalPosWhereCanReadDWordFromInputBuffer - pInputBuffer) >= 5)
{
ulong thisQWord = Unsafe.ReadUnaligned <ulong>(pInputBuffer);
// Stage the next 32 bits into 'thisDWord' so that it's ready for us in case we need to jump backward
// to a previous location in the loop. This offers defense against reading main memory again (which may
// have been modified and could lead to a race condition).
thisDWord = (uint)thisQWord;
// Is this three 3-byte sequences in a row?
// thisQWord = [ 10yyyyyy 1110zzzz | 10xxxxxx 10yyyyyy 1110zzzz | 10xxxxxx 10yyyyyy 1110zzzz ] [ 10xxxxxx ]
// ---- CHAR 3 ---- --------- CHAR 2 --------- --------- CHAR 1 --------- -CHAR 3-
if ((thisQWord & 0xC0F0_C0C0_F0C0_C0F0ul) == 0x80E0_8080_E080_80E0ul && Utf8Utility.IsUtf8ContinuationByte(in pInputBuffer[8]))
{
// Saw a proper bitmask for three incoming 3-byte sequences, perform the
// overlong and surrogate sequence checking now.
// Check the first character.
// If the first character is overlong or a surrogate, fail immediately.
if ((0u >= ((uint)thisQWord & 0x200Fu)) || (0u >= (((uint)thisQWord - 0x200Du) & 0x200Fu)))
{
goto Error;
}
// Check the second character.
// At this point, we now know the first three bytes represent a well-formed sequence.
// If there's an error beyond here, we'll jump back to the "process three known good bytes"
// logic.
thisQWord >>= 24;
if ((0u >= ((uint)thisQWord & 0x200Fu)) || (0u >= (((uint)thisQWord - 0x200Du) & 0x200Fu)))
{
goto ProcessSingleThreeByteSequenceSkipOverlongAndSurrogateChecks;
}
// Check the third character (we already checked that it's followed by a continuation byte).
thisQWord >>= 24;
if ((0u >= ((uint)thisQWord & 0x200Fu)) || (0u >= (((uint)thisQWord - 0x200Du) & 0x200Fu)))
{
goto ProcessSingleThreeByteSequenceSkipOverlongAndSurrogateChecks;
}
pInputBuffer += 9;
tempUtf16CodeUnitCountAdjustment -= 6; // 9 UTF-8 bytes -> 3 UTF-16 code units (and 3 scalars)
goto SuccessfullyProcessedThreeByteSequence;
}
// Is this two 3-byte sequences in a row?
// thisQWord = [ ######## ######## | 10xxxxxx 10yyyyyy 1110zzzz | 10xxxxxx 10yyyyyy 1110zzzz ]
// --------- CHAR 2 --------- --------- CHAR 1 ---------
if ((thisQWord & 0xC0C0_F0C0_C0F0ul) == 0x8080_E080_80E0ul)
{
// Saw a proper bitmask for two incoming 3-byte sequences, perform the
// overlong and surrogate sequence checking now.
// Check the first character.
// If the first character is overlong or a surrogate, fail immediately.
if ((0u >= ((uint)thisQWord & 0x200Fu)) || (0u >= (((uint)thisQWord - 0x200Du) & 0x200Fu)))
{
goto Error;
}
// Check the second character.
// At this point, we now know the first three bytes represent a well-formed sequence.
// If there's an error beyond here, we'll jump back to the "process three known good bytes"
// logic.
thisQWord >>= 24;
if ((0u >= ((uint)thisQWord & 0x200Fu)) || (0u >= (((uint)thisQWord - 0x200Du) & 0x200Fu)))
{
goto ProcessSingleThreeByteSequenceSkipOverlongAndSurrogateChecks;
}
pInputBuffer += 6;
tempUtf16CodeUnitCountAdjustment -= 4; // 6 UTF-8 bytes -> 2 UTF-16 code units (and 2 scalars)
// The next byte in the sequence didn't have a 3-byte marker, so it's probably
// an ASCII character. Jump back to the beginning of loop processing.
continue;
}
if (Utf8Utility.UInt32BeginsWithUtf8ThreeByteMask(thisDWord))
{
// A single three-byte sequence.
goto ProcessThreeByteSequenceWithCheck;
}
else
{
// Not a three-byte sequence; perhaps ASCII?
goto AfterReadDWord;
}
}
}
if (pInputBuffer <= pFinalPosWhereCanReadDWordFromInputBuffer)
{
thisDWord = Unsafe.ReadUnaligned <uint>(pInputBuffer);
// Optimization: A three-byte character could indicate CJK text, which makes it likely
// that the character following this one is also CJK. We'll check for a three-byte sequence
// marker now and jump directly to three-byte sequence processing if we see one, skipping
// all of the logic at the beginning of the loop.
if (Utf8Utility.UInt32BeginsWithUtf8ThreeByteMask(thisDWord))
{
goto ProcessThreeByteSequenceWithCheck; // Found another [not yet validated] three-byte sequence; process
}
else
{
goto AfterReadDWord; // Probably ASCII punctuation or whitespace; go back to start of loop
}
}
else
{
goto ProcessRemainingBytesSlow; // Running out of data
}
}
// Assume the 4-byte case, but we need to validate.
if (BitConverter.IsLittleEndian)
{
thisDWord &= 0xC0C0_FFFFu;
// After the above modifications earlier in this method, we expect 'thisDWord'
// to have the structure [ 10000000 00000000 00uuzzzz 00010uuu ]. We'll now
// perform two checks to confirm this. The first will verify the
// [ 10000000 00000000 00###### ######## ] structure by taking advantage of two's
// complement representation to perform a single *signed* integer check.
if ((int)thisDWord > unchecked ((int)0x8000_3FFF))
{
goto Error; // didn't have three trailing bytes
}
// Now we want to confirm that 0x01 <= uuuuu (otherwise this is an overlong encoding)
// and that uuuuu <= 0x10 (otherwise this is an out-of-range encoding).
thisDWord = BitOperations.RotateRight(thisDWord, 8);
// Now, thisDWord = [ 00010uuu 10000000 00000000 00uuzzzz ].
// The check is now a simple add / cmp / jcc combo.
if (!UnicodeUtility.IsInRangeInclusive(thisDWord, 0x1080_0010u, 0x1480_000Fu))
{
goto Error; // overlong or out-of-range
}
}
else
{
thisDWord -= 0x80u;
// After the above modifications earlier in this method, we expect 'thisDWord'
// to have the structure [ 00010uuu 00uuzzzz 00yyyyyy 00xxxxxx ]. We'll now
// perform two checks to confirm this. The first will verify the
// [ ######## 00###### 00###### 00###### ] structure.
if ((thisDWord & 0x00C0_C0C0u) != 0)
{
goto Error; // didn't have three trailing bytes
}
// Now we want to confirm that 0x01 <= uuuuu (otherwise this is an overlong encoding)
// and that uuuuu <= 0x10 (otherwise this is an out-of-range encoding).
// This is a simple range check. (We don't care about the low two bytes.)
if (!UnicodeUtility.IsInRangeInclusive(thisDWord, 0x1010_0000u, 0x140F_FFFFu))
{
goto Error; // overlong or out-of-range
}
}
// Validation of 4-byte case complete.
pInputBuffer += 4;
tempUtf16CodeUnitCountAdjustment -= 2; // 4 UTF-8 bytes -> 2 UTF-16 code units
tempScalarCountAdjustment--; // 2 UTF-16 code units -> 1 scalar
continue; // go back to beginning of loop for processing
}
goto ProcessRemainingBytesSlow;
ProcessInputOfLessThanDWordSize:
Debug.Assert(inputLength < 4);
nuint inputBufferRemainingBytes = (uint)inputLength;
goto ProcessSmallBufferCommon;
ProcessRemainingBytesSlow:
inputBufferRemainingBytes = (nuint)(void *)Unsafe.ByteOffset(ref *pInputBuffer, ref *pFinalPosWhereCanReadDWordFromInputBuffer) + 4;
ProcessSmallBufferCommon:
Debug.Assert(inputBufferRemainingBytes < 4);
while (inputBufferRemainingBytes > 0)
{
uint firstByte = pInputBuffer[0];
if ((byte)firstByte < 0x80u)
{
// 1-byte (ASCII) case
pInputBuffer++;
inputBufferRemainingBytes--;
continue;
}
else if (inputBufferRemainingBytes >= 2)
{
uint secondByte = pInputBuffer[1]; // typed as 32-bit since we perform arithmetic (not just comparisons) on this value
if ((byte)firstByte < 0xE0u)
{
// 2-byte case
if ((byte)firstByte >= 0xC2u && Utf8Utility.IsLowByteUtf8ContinuationByte(secondByte))
{
pInputBuffer += 2;
tempUtf16CodeUnitCountAdjustment--; // 2 UTF-8 bytes -> 1 UTF-16 code unit (and 1 scalar)
inputBufferRemainingBytes -= 2;
continue;
}
}
else if (inputBufferRemainingBytes >= 3)
{
if ((byte)firstByte < 0xF0u)
{
if ((byte)firstByte == 0xE0u)
{
if (!UnicodeUtility.IsInRangeInclusive(secondByte, 0xA0u, 0xBFu))
{
goto Error; // overlong encoding
}
}
else if ((byte)firstByte == 0xEDu)
{
if (!UnicodeUtility.IsInRangeInclusive(secondByte, 0x80u, 0x9Fu))
{
goto Error; // would be a UTF-16 surrogate code point
}
}
else
{
if (!Utf8Utility.IsLowByteUtf8ContinuationByte(secondByte))
{
goto Error; // first trailing byte doesn't have proper continuation marker
}
}
if (Utf8Utility.IsUtf8ContinuationByte(in pInputBuffer[2]))
{
pInputBuffer += 3;
tempUtf16CodeUnitCountAdjustment -= 2; // 3 UTF-8 bytes -> 2 UTF-16 code units (and 2 scalars)
inputBufferRemainingBytes -= 3;
continue;
}
}
}
}
// Error - no match.
goto Error;
}
// If we reached this point, we're out of data, and we saw no bad UTF8 sequence.
#if DEBUG
// Quick check that for the success case we're going to fulfill our contract of returning &inputBuffer[inputLength].
Debug.Assert(pOriginalInputBuffer + originalInputLength == pInputBuffer, "About to return an unexpected value.");
#endif
Error:
// Report back to our caller how far we got before seeing invalid data.
// (Also used for normal termination when falling out of the loop above.)
utf16CodeUnitCountAdjustment = tempUtf16CodeUnitCountAdjustment;
scalarCountAdjustment = tempScalarCountAdjustment;
return(pInputBuffer);
}