Add m-esr52 at 52.6.0

1 files changed, 1067 insertions, 0 deletions

diff --git a/image/decoders/nsBMPDecoder.cpp b/image/decoders/nsBMPDecoder.cpp
new file mode 100644
index 000000000..1f0449e4e
--- /dev/null
+++ b/image/decoders/nsBMPDecoder.cpp
@@ -0,0 +1,1067 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This is a cross-platform BMP Decoder, which should work everywhere,
+// including big-endian machines like the PowerPC.
+//
+// BMP is a format that has been extended multiple times. To understand the
+// decoder you need to understand this history. The summary of the history
+// below was determined from the following documents.
+//
+// - http://www.fileformat.info/format/bmp/egff.htm
+// - http://www.fileformat.info/format/os2bmp/egff.htm
+// - http://fileformats.archiveteam.org/wiki/BMP
+// - http://fileformats.archiveteam.org/wiki/OS/2_BMP
+// - https://en.wikipedia.org/wiki/BMP_file_format
+// - https://upload.wikimedia.org/wikipedia/commons/c/c4/BMPfileFormat.png
+//
+// WINDOWS VERSIONS OF THE BMP FORMAT
+// ----------------------------------
+// WinBMPv1.
+// - This version is no longer used and can be ignored.
+//
+// WinBMPv2.
+// - First is a 14 byte file header that includes: the magic number ("BM"),
+//   file size, and offset to the pixel data (|mDataOffset|).
+// - Next is a 12 byte info header which includes: the info header size
+//   (mBIHSize), width, height, number of color planes, and bits-per-pixel
+//   (|mBpp|) which must be 1, 4, 8 or 24.
+// - Next is the semi-optional color table, which has length 2^|mBpp| and has 3
+//   bytes per value (BGR). The color table is required if |mBpp| is 1, 4, or 8.
+// - Next is an optional gap.
+// - Next is the pixel data, which is pointed to by |mDataOffset|.
+//
+// WinBMPv3. This is the most widely used version.
+// - It changed the info header to 40 bytes by taking the WinBMPv2 info
+//   header, enlargening its width and height fields, and adding more fields
+//   including: a compression type (|mCompression|) and number of colors
+//   (|mNumColors|).
+// - The semi-optional color table is now 4 bytes per value (BGR0), and its
+//   length is |mNumColors|, or 2^|mBpp| if |mNumColors| is zero.
+// - |mCompression| can be RGB (i.e. no compression), RLE4 (if |mBpp|==4) or
+//   RLE8 (if |mBpp|==8) values.
+//
+// WinBMPv3-NT. A variant of WinBMPv3.
+// - It did not change the info header layout from WinBMPv3.
+// - |mBpp| can now be 16 or 32, in which case |mCompression| can be RGB or the
+//   new BITFIELDS value; in the latter case an additional 12 bytes of color
+//   bitfields follow the info header.
+//
+// WinBMPv4.
+// - It extended the info header to 108 bytes, including the 12 bytes of color
+//   mask data from WinBMPv3-NT, plus alpha mask data, and also color-space and
+//   gamma correction fields.
+//
+// WinBMPv5.
+// - It extended the info header to 124 bytes, adding color profile data.
+// - It also added an optional color profile table after the pixel data (and
+//   another optional gap).
+//
+// WinBMPv3-ICO. This is a variant of WinBMPv3.
+// - It's the BMP format used for BMP images within ICO files.
+// - The only difference with WinBMPv3 is that if an image is 32bpp and has no
+//   compression, then instead of treating the pixel data as 0RGB it is treated
+//   as ARGB, but only if one or more of the A values are non-zero.
+//
+// OS/2 VERSIONS OF THE BMP FORMAT
+// -------------------------------
+// OS2-BMPv1.
+// - Almost identical to WinBMPv2; the differences are basically ignorable.
+//
+// OS2-BMPv2.
+// - Similar to WinBMPv3.
+// - The info header is 64 bytes but can be reduced to as little as 16; any
+//   omitted fields are treated as zero. The first 40 bytes of these fields are
+//   nearly identical to the WinBMPv3 info header; the remaining 24 bytes are
+//   different.
+// - Also adds compression types "Huffman 1D" and "RLE24", which we don't
+//   support.
+// - We treat OS2-BMPv2 files as if they are WinBMPv3 (i.e. ignore the extra 24
+//   bytes in the info header), which in practice is good enough.
+
+#include "ImageLogging.h"
+#include "nsBMPDecoder.h"
+
+#include <stdlib.h>
+
+#include "mozilla/Attributes.h"
+#include "mozilla/EndianUtils.h"
+#include "mozilla/Likely.h"
+
+#include "nsIInputStream.h"
+#include "RasterImage.h"
+#include <algorithm>
+
+using namespace mozilla::gfx;
+
+namespace mozilla {
+namespace image {
+namespace bmp {
+
+struct Compression {
+  enum {
+    RGB = 0,
+    RLE8 = 1,
+    RLE4 = 2,
+    BITFIELDS = 3
+  };
+};
+
+// RLE escape codes and constants.
+struct RLE {
+  enum {
+    ESCAPE = 0,
+    ESCAPE_EOL = 0,
+    ESCAPE_EOF = 1,
+    ESCAPE_DELTA = 2,
+
+    SEGMENT_LENGTH = 2,
+    DELTA_LENGTH = 2
+  };
+};
+
+} // namespace bmp
+
+using namespace bmp;
+
+/// Sets the pixel data in aDecoded to the given values.
+/// @param aDecoded pointer to pixel to be set, will be incremented to point to
+/// the next pixel.
+static void
+SetPixel(uint32_t*& aDecoded, uint8_t aRed, uint8_t aGreen,
+         uint8_t aBlue, uint8_t aAlpha = 0xFF)
+{
+  *aDecoded++ = gfxPackedPixel(aAlpha, aRed, aGreen, aBlue);
+}
+
+static void
+SetPixel(uint32_t*& aDecoded, uint8_t idx,
+         const UniquePtr<ColorTableEntry[]>& aColors)
+{
+  SetPixel(aDecoded,
+           aColors[idx].mRed, aColors[idx].mGreen, aColors[idx].mBlue);
+}
+
+/// Sets two (or one if aCount = 1) pixels
+/// @param aDecoded where the data is stored. Will be moved 4 resp 8 bytes
+/// depending on whether one or two pixels are written.
+/// @param aData The values for the two pixels
+/// @param aCount Current count. Is decremented by one or two.
+static void
+Set4BitPixel(uint32_t*& aDecoded, uint8_t aData, uint32_t& aCount,
+             const UniquePtr<ColorTableEntry[]>& aColors)
+{
+  uint8_t idx = aData >> 4;
+  SetPixel(aDecoded, idx, aColors);
+  if (--aCount > 0) {
+    idx = aData & 0xF;
+    SetPixel(aDecoded, idx, aColors);
+    --aCount;
+  }
+}
+
+static mozilla::LazyLogModule sBMPLog("BMPDecoder");
+
+// The length of the mBIHSize field in the info header.
+static const uint32_t BIHSIZE_FIELD_LENGTH = 4;
+
+nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength)
+  : Decoder(aImage)
+  , mLexer(Transition::To(aState, aLength), Transition::TerminateSuccess())
+  , mIsWithinICO(false)
+  , mMayHaveTransparency(false)
+  , mDoesHaveTransparency(false)
+  , mNumColors(0)
+  , mColors(nullptr)
+  , mBytesPerColor(0)
+  , mPreGapLength(0)
+  , mPixelRowSize(0)
+  , mCurrentRow(0)
+  , mCurrentPos(0)
+  , mAbsoluteModeNumPixels(0)
+{
+}
+
+// Constructor for normal BMP files.
+nsBMPDecoder::nsBMPDecoder(RasterImage* aImage)
+  : nsBMPDecoder(aImage, State::FILE_HEADER, FILE_HEADER_LENGTH)
+{
+}
+
+// Constructor used for WinBMPv3-ICO files, which lack a file header.
+nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, uint32_t aDataOffset)
+  : nsBMPDecoder(aImage, State::INFO_HEADER_SIZE, BIHSIZE_FIELD_LENGTH)
+{
+  SetIsWithinICO();
+
+  // Even though the file header isn't present in this case, the dataOffset
+  // field is set as if it is, and so we must increment mPreGapLength
+  // accordingly.
+  mPreGapLength += FILE_HEADER_LENGTH;
+
+  // This is the one piece of data we normally get from a BMP file header, so
+  // it must be provided via an argument.
+  mH.mDataOffset = aDataOffset;
+}
+
+nsBMPDecoder::~nsBMPDecoder()
+{
+}
+
+// Obtains the size of the compressed image resource.
+int32_t
+nsBMPDecoder::GetCompressedImageSize() const
+{
+  // In the RGB case mImageSize might not be set, so compute it manually.
+  MOZ_ASSERT(mPixelRowSize != 0);
+  return mH.mCompression == Compression::RGB
+       ? mPixelRowSize * AbsoluteHeight()
+       : mH.mImageSize;
+}
+
+nsresult
+nsBMPDecoder::BeforeFinishInternal()
+{
+  if (!IsMetadataDecode() && !mImageData) {
+    return NS_ERROR_FAILURE;  // No image; something went wrong.
+  }
+
+  return NS_OK;
+}
+
+nsresult
+nsBMPDecoder::FinishInternal()
+{
+  // We shouldn't be called in error cases.
+  MOZ_ASSERT(!HasError(), "Can't call FinishInternal on error!");
+
+  // We should never make multiple frames.
+  MOZ_ASSERT(GetFrameCount() <= 1, "Multiple BMP frames?");
+
+  // Send notifications if appropriate.
+  if (!IsMetadataDecode() && HasSize()) {
+
+    // We should have image data.
+    MOZ_ASSERT(mImageData);
+
+    // If it was truncated, fill in the missing pixels as black.
+    while (mCurrentRow > 0) {
+      uint32_t* dst = RowBuffer();
+      while (mCurrentPos < mH.mWidth) {
+        SetPixel(dst, 0, 0, 0);
+        mCurrentPos++;
+      }
+      mCurrentPos = 0;
+      FinishRow();
+    }
+
+    // Invalidate.
+    nsIntRect r(0, 0, mH.mWidth, AbsoluteHeight());
+    PostInvalidation(r);
+
+    MOZ_ASSERT_IF(mDoesHaveTransparency, mMayHaveTransparency);
+
+    // We have transparency if we either detected some in the image itself
+    // (i.e., |mDoesHaveTransparency| is true) or we're in an ICO, which could
+    // mean we have an AND mask that provides transparency (i.e., |mIsWithinICO|
+    // is true).
+    // XXX(seth): We can tell when we create the decoder if the AND mask is
+    // present, so we could be more precise about this.
+    const Opacity opacity = mDoesHaveTransparency || mIsWithinICO
+                          ? Opacity::SOME_TRANSPARENCY
+                          : Opacity::FULLY_OPAQUE;
+
+    PostFrameStop(opacity);
+    PostDecodeDone();
+  }
+
+  return NS_OK;
+}
+
+// ----------------------------------------
+// Actual Data Processing
+// ----------------------------------------
+
+void
+BitFields::Value::Set(uint32_t aMask)
+{
+  mMask = aMask;
+
+  // Handle this exceptional case first. The chosen values don't matter
+  // (because a mask of zero will always give a value of zero) except that
+  // mBitWidth:
+  // - shouldn't be zero, because that would cause an infinite loop in Get();
+  // - shouldn't be 5 or 8, because that could cause a false positive match in
+  //   IsR5G5B5() or IsR8G8B8().
+  if (mMask == 0x0) {
+    mRightShift = 0;
+    mBitWidth = 1;
+    return;
+  }
+
+  // Find the rightmost 1.
+  uint8_t i;
+  for (i = 0; i < 32; i++) {
+    if (mMask & (1 << i)) {
+      break;
+    }
+  }
+  mRightShift = i;
+
+  // Now find the leftmost 1 in the same run of 1s. (If there are multiple runs
+  // of 1s -- which isn't valid -- we'll behave as if only the lowest run was
+  // present, which seems reasonable.)
+  for (i = i + 1; i < 32; i++) {
+    if (!(mMask & (1 << i))) {
+      break;
+    }
+  }
+  mBitWidth = i - mRightShift;
+}
+
+MOZ_ALWAYS_INLINE uint8_t
+BitFields::Value::Get(uint32_t aValue) const
+{
+  // Extract the unscaled value.
+  uint32_t v = (aValue & mMask) >> mRightShift;
+
+  // Idea: to upscale v precisely we need to duplicate its bits, possibly
+  // repeatedly, possibly partially in the last case, from bit 7 down to bit 0
+  // in v2. For example:
+  //
+  // - mBitWidth=1:  v2 = v<<7 | v<<6 | ... | v<<1 | v>>0     k -> kkkkkkkk
+  // - mBitWidth=2:  v2 = v<<6 | v<<4 | v<<2 | v>>0          jk -> jkjkjkjk
+  // - mBitWidth=3:  v2 = v<<5 | v<<2 | v>>1                ijk -> ijkijkij
+  // - mBitWidth=4:  v2 = v<<4 | v>>0                      hijk -> hijkhijk
+  // - mBitWidth=5:  v2 = v<<3 | v>>2                     ghijk -> ghijkghi
+  // - mBitWidth=6:  v2 = v<<2 | v>>4                    fghijk -> fghijkfg
+  // - mBitWidth=7:  v2 = v<<1 | v>>6                   efghijk -> efghijke
+  // - mBitWidth=8:  v2 = v>>0                         defghijk -> defghijk
+  // - mBitWidth=9:  v2 = v>>1                        cdefghijk -> cdefghij
+  // - mBitWidth=10: v2 = v>>2                       bcdefghijk -> bcdefghi
+  // - mBitWidth=11: v2 = v>>3                      abcdefghijk -> abcdefgh
+  // - etc.
+  //
+  uint8_t v2 = 0;
+  int32_t i;      // must be a signed integer
+  for (i = 8 - mBitWidth; i > 0; i -= mBitWidth) {
+    v2 |= v << uint32_t(i);
+  }
+  v2 |= v >> uint32_t(-i);
+  return v2;
+}
+
+MOZ_ALWAYS_INLINE uint8_t
+BitFields::Value::GetAlpha(uint32_t aValue, bool& aHasAlphaOut) const
+{
+  if (mMask == 0x0) {
+    return 0xff;
+  }
+  aHasAlphaOut = true;
+  return Get(aValue);
+}
+
+MOZ_ALWAYS_INLINE uint8_t
+BitFields::Value::Get5(uint32_t aValue) const
+{
+  MOZ_ASSERT(mBitWidth == 5);
+  uint32_t v = (aValue & mMask) >> mRightShift;
+  return (v << 3u) | (v >> 2u);
+}
+
+MOZ_ALWAYS_INLINE uint8_t
+BitFields::Value::Get8(uint32_t aValue) const
+{
+  MOZ_ASSERT(mBitWidth == 8);
+  uint32_t v = (aValue & mMask) >> mRightShift;
+  return v;
+}
+
+void
+BitFields::SetR5G5B5()
+{
+  mRed.Set(0x7c00);
+  mGreen.Set(0x03e0);
+  mBlue.Set(0x001f);
+}
+
+void
+BitFields::SetR8G8B8()
+{
+  mRed.Set(0xff0000);
+  mGreen.Set(0xff00);
+  mBlue.Set(0x00ff);
+}
+
+bool
+BitFields::IsR5G5B5() const
+{
+  return mRed.mBitWidth == 5 &&
+         mGreen.mBitWidth == 5 &&
+         mBlue.mBitWidth == 5 &&
+         mAlpha.mMask == 0x0;
+}
+
+bool
+BitFields::IsR8G8B8() const
+{
+  return mRed.mBitWidth == 8 &&
+         mGreen.mBitWidth == 8 &&
+         mBlue.mBitWidth == 8 &&
+         mAlpha.mMask == 0x0;
+}
+
+uint32_t*
+nsBMPDecoder::RowBuffer()
+{
+  if (mDownscaler) {
+    return reinterpret_cast<uint32_t*>(mDownscaler->RowBuffer()) + mCurrentPos;
+  }
+
+  // Convert from row (1..mHeight) to absolute line (0..mHeight-1).
+  int32_t line = (mH.mHeight < 0)
+               ? -mH.mHeight - mCurrentRow
+               : mCurrentRow - 1;
+  int32_t offset = line * mH.mWidth + mCurrentPos;
+  return reinterpret_cast<uint32_t*>(mImageData) + offset;
+}
+
+void
+nsBMPDecoder::FinishRow()
+{
+  if (mDownscaler) {
+    mDownscaler->CommitRow();
+
+    if (mDownscaler->HasInvalidation()) {
+      DownscalerInvalidRect invalidRect = mDownscaler->TakeInvalidRect();
+      PostInvalidation(invalidRect.mOriginalSizeRect,
+                       Some(invalidRect.mTargetSizeRect));
+    }
+  } else {
+    PostInvalidation(IntRect(0, mCurrentRow, mH.mWidth, 1));
+  }
+  mCurrentRow--;
+}
+
+LexerResult
+nsBMPDecoder::DoDecode(SourceBufferIterator& aIterator, IResumable* aOnResume)
+{
+  MOZ_ASSERT(!HasError(), "Shouldn't call DoDecode after error!");
+
+  return mLexer.Lex(aIterator, aOnResume,
+                    [=](State aState, const char* aData, size_t aLength) {
+    switch (aState) {
+      case State::FILE_HEADER:      return ReadFileHeader(aData, aLength);
+      case State::INFO_HEADER_SIZE: return ReadInfoHeaderSize(aData, aLength);
+      case State::INFO_HEADER_REST: return ReadInfoHeaderRest(aData, aLength);
+      case State::BITFIELDS:        return ReadBitfields(aData, aLength);
+      case State::COLOR_TABLE:      return ReadColorTable(aData, aLength);
+      case State::GAP:              return SkipGap();
+      case State::AFTER_GAP:        return AfterGap();
+      case State::PIXEL_ROW:        return ReadPixelRow(aData);
+      case State::RLE_SEGMENT:      return ReadRLESegment(aData);
+      case State::RLE_DELTA:        return ReadRLEDelta(aData);
+      case State::RLE_ABSOLUTE:     return ReadRLEAbsolute(aData, aLength);
+      default:
+        MOZ_CRASH("Unknown State");
+    }
+  });
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadFileHeader(const char* aData, size_t aLength)
+{
+  mPreGapLength += aLength;
+
+  bool signatureOk = aData[0] == 'B' && aData[1] == 'M';
+  if (!signatureOk) {
+    return Transition::TerminateFailure();
+  }
+
+  // We ignore the filesize (aData + 2) and reserved (aData + 6) fields.
+
+  mH.mDataOffset = LittleEndian::readUint32(aData + 10);
+
+  return Transition::To(State::INFO_HEADER_SIZE, BIHSIZE_FIELD_LENGTH);
+}
+
+// We read the info header in two steps: (a) read the mBIHSize field to
+// determine how long the header is; (b) read the rest of the header.
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadInfoHeaderSize(const char* aData, size_t aLength)
+{
+  mPreGapLength += aLength;
+
+  mH.mBIHSize = LittleEndian::readUint32(aData);
+
+  bool bihSizeOk = mH.mBIHSize == InfoHeaderLength::WIN_V2 ||
+                   mH.mBIHSize == InfoHeaderLength::WIN_V3 ||
+                   mH.mBIHSize == InfoHeaderLength::WIN_V4 ||
+                   mH.mBIHSize == InfoHeaderLength::WIN_V5 ||
+                   (mH.mBIHSize >= InfoHeaderLength::OS2_V2_MIN &&
+                    mH.mBIHSize <= InfoHeaderLength::OS2_V2_MAX);
+  if (!bihSizeOk) {
+    return Transition::TerminateFailure();
+  }
+  // ICO BMPs must have a WinBMPv3 header. nsICODecoder should have already
+  // terminated decoding if this isn't the case.
+  MOZ_ASSERT_IF(mIsWithinICO, mH.mBIHSize == InfoHeaderLength::WIN_V3);
+
+  return Transition::To(State::INFO_HEADER_REST,
+                        mH.mBIHSize - BIHSIZE_FIELD_LENGTH);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadInfoHeaderRest(const char* aData, size_t aLength)
+{
+  mPreGapLength += aLength;
+
+  // |mWidth| and |mHeight| may be signed (Windows) or unsigned (OS/2). We just
+  // read as unsigned because in practice that's good enough.
+  if (mH.mBIHSize == InfoHeaderLength::WIN_V2) {
+    mH.mWidth  = LittleEndian::readUint16(aData + 0);
+    mH.mHeight = LittleEndian::readUint16(aData + 2);
+    // We ignore the planes (aData + 4) field; it should always be 1.
+    mH.mBpp    = LittleEndian::readUint16(aData + 6);
+  } else {
+    mH.mWidth  = LittleEndian::readUint32(aData + 0);
+    mH.mHeight = LittleEndian::readUint32(aData + 4);
+    // We ignore the planes (aData + 4) field; it should always be 1.
+    mH.mBpp    = LittleEndian::readUint16(aData + 10);
+
+    // For OS2-BMPv2 the info header may be as little as 16 bytes, so be
+    // careful for these fields.
+    mH.mCompression = aLength >= 16 ? LittleEndian::readUint32(aData + 12) : 0;
+    mH.mImageSize   = aLength >= 20 ? LittleEndian::readUint32(aData + 16) : 0;
+    // We ignore the xppm (aData + 20) and yppm (aData + 24) fields.
+    mH.mNumColors   = aLength >= 32 ? LittleEndian::readUint32(aData + 28) : 0;
+    // We ignore the important_colors (aData + 36) field.
+
+    // For WinBMPv4, WinBMPv5 and (possibly) OS2-BMPv2 there are additional
+    // fields in the info header which we ignore, with the possible exception
+    // of the color bitfields (see below).
+  }
+
+  // Run with MOZ_LOG=BMPDecoder:5 set to see this output.
+  MOZ_LOG(sBMPLog, LogLevel::Debug,
+          ("BMP: bihsize=%u, %d x %d, bpp=%u, compression=%u, colors=%u\n",
+          mH.mBIHSize, mH.mWidth, mH.mHeight, uint32_t(mH.mBpp),
+          mH.mCompression, mH.mNumColors));
+
+  // BMPs with negative width are invalid. Also, reject extremely wide images
+  // to keep the math sane. And reject INT_MIN as a height because you can't
+  // get its absolute value (because -INT_MIN is one more than INT_MAX).
+  const int32_t k64KWidth = 0x0000FFFF;
+  bool sizeOk = 0 <= mH.mWidth && mH.mWidth <= k64KWidth &&
+                mH.mHeight != INT_MIN;
+  if (!sizeOk) {
+    return Transition::TerminateFailure();
+  }
+
+  // Check mBpp and mCompression.
+  bool bppCompressionOk =
+    (mH.mCompression == Compression::RGB &&
+      (mH.mBpp ==  1 || mH.mBpp ==  4 || mH.mBpp ==  8 ||
+       mH.mBpp == 16 || mH.mBpp == 24 || mH.mBpp == 32)) ||
+    (mH.mCompression == Compression::RLE8 && mH.mBpp == 8) ||
+    (mH.mCompression == Compression::RLE4 && mH.mBpp == 4) ||
+    (mH.mCompression == Compression::BITFIELDS &&
+      // For BITFIELDS compression we require an exact match for one of the
+      // WinBMP BIH sizes; this clearly isn't an OS2 BMP.
+      (mH.mBIHSize == InfoHeaderLength::WIN_V3 ||
+       mH.mBIHSize == InfoHeaderLength::WIN_V4 ||
+       mH.mBIHSize == InfoHeaderLength::WIN_V5) &&
+      (mH.mBpp == 16 || mH.mBpp == 32));
+  if (!bppCompressionOk) {
+    return Transition::TerminateFailure();
+  }
+
+  // Initialize our current row to the top of the image.
+  mCurrentRow = AbsoluteHeight();
+
+  // Round it up to the nearest byte count, then pad to 4-byte boundary.
+  // Compute this even for a metadate decode because GetCompressedImageSize()
+  // relies on it.
+  mPixelRowSize = (mH.mBpp * mH.mWidth + 7) / 8;
+  uint32_t surplus = mPixelRowSize % 4;
+  if (surplus != 0) {
+    mPixelRowSize += 4 - surplus;
+  }
+
+  size_t bitFieldsLengthStillToRead = 0;
+  if (mH.mCompression == Compression::BITFIELDS) {
+    // Need to read bitfields.
+    if (mH.mBIHSize >= InfoHeaderLength::WIN_V4) {
+      // Bitfields are present in the info header, so we can read them
+      // immediately.
+      mBitFields.ReadFromHeader(aData + 36, /* aReadAlpha = */ true);
+    } else {
+      // Bitfields are present after the info header, so we will read them in
+      // ReadBitfields().
+      bitFieldsLengthStillToRead = BitFields::LENGTH;
+    }
+  } else if (mH.mBpp == 16) {
+    // No bitfields specified; use the default 5-5-5 values.
+    mBitFields.SetR5G5B5();
+  } else if (mH.mBpp == 32) {
+    // No bitfields specified; use the default 8-8-8 values.
+    mBitFields.SetR8G8B8();
+  }
+
+  return Transition::To(State::BITFIELDS, bitFieldsLengthStillToRead);
+}
+
+void
+BitFields::ReadFromHeader(const char* aData, bool aReadAlpha)
+{
+  mRed.Set  (LittleEndian::readUint32(aData + 0));
+  mGreen.Set(LittleEndian::readUint32(aData + 4));
+  mBlue.Set (LittleEndian::readUint32(aData + 8));
+  if (aReadAlpha) {
+    mAlpha.Set(LittleEndian::readUint32(aData + 12));
+  }
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadBitfields(const char* aData, size_t aLength)
+{
+  mPreGapLength += aLength;
+
+  // If aLength is zero there are no bitfields to read, or we already read them
+  // in ReadInfoHeader().
+  if (aLength != 0) {
+    mBitFields.ReadFromHeader(aData, /* aReadAlpha = */ false);
+  }
+
+  // Note that RLE-encoded BMPs might be transparent because the 'delta' mode
+  // can skip pixels and cause implicit transparency.
+  mMayHaveTransparency =
+    mIsWithinICO ||
+    mH.mCompression == Compression::RLE8 ||
+    mH.mCompression == Compression::RLE4 ||
+    (mH.mCompression == Compression::BITFIELDS &&
+     mBitFields.mAlpha.IsPresent());
+  if (mMayHaveTransparency) {
+    PostHasTransparency();
+  }
+
+  // Post our size to the superclass.
+  PostSize(mH.mWidth, AbsoluteHeight());
+
+  // We've now read all the headers. If we're doing a metadata decode, we're
+  // done.
+  if (IsMetadataDecode()) {
+    return Transition::TerminateSuccess();
+  }
+
+  // Set up the color table, if present; it'll be filled in by ReadColorTable().
+  if (mH.mBpp <= 8) {
+    mNumColors = 1 << mH.mBpp;
+    if (0 < mH.mNumColors && mH.mNumColors < mNumColors) {
+      mNumColors = mH.mNumColors;
+    }
+
+    // Always allocate and zero 256 entries, even though mNumColors might be
+    // smaller, because the file might erroneously index past mNumColors.
+    mColors = MakeUnique<ColorTableEntry[]>(256);
+    memset(mColors.get(), 0, 256 * sizeof(ColorTableEntry));
+
+    // OS/2 Bitmaps have no padding byte.
+    mBytesPerColor = (mH.mBIHSize == InfoHeaderLength::WIN_V2) ? 3 : 4;
+  }
+
+  MOZ_ASSERT(!mImageData, "Already have a buffer allocated?");
+  nsresult rv = AllocateFrame(/* aFrameNum = */ 0, OutputSize(),
+                              FullOutputFrame(),
+                              mMayHaveTransparency ? SurfaceFormat::B8G8R8A8
+                                                   : SurfaceFormat::B8G8R8X8);
+  if (NS_FAILED(rv)) {
+    return Transition::TerminateFailure();
+  }
+  MOZ_ASSERT(mImageData, "Should have a buffer now");
+
+  if (mDownscaler) {
+    // BMPs store their rows in reverse order, so the downscaler needs to
+    // reverse them again when writing its output. Unless the height is
+    // negative!
+    rv = mDownscaler->BeginFrame(Size(), Nothing(),
+                                 mImageData, mMayHaveTransparency,
+                                 /* aFlipVertically = */ mH.mHeight >= 0);
+    if (NS_FAILED(rv)) {
+      return Transition::TerminateFailure();
+    }
+  }
+
+  return Transition::To(State::COLOR_TABLE, mNumColors * mBytesPerColor);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadColorTable(const char* aData, size_t aLength)
+{
+  MOZ_ASSERT_IF(aLength != 0, mNumColors > 0 && mColors);
+
+  mPreGapLength += aLength;
+
+  for (uint32_t i = 0; i < mNumColors; i++) {
+    // The format is BGR or BGR0.
+    mColors[i].mBlue  = uint8_t(aData[0]);
+    mColors[i].mGreen = uint8_t(aData[1]);
+    mColors[i].mRed   = uint8_t(aData[2]);
+    aData += mBytesPerColor;
+  }
+
+  // We know how many bytes we've read so far (mPreGapLength) and we know the
+  // offset of the pixel data (mH.mDataOffset), so we can determine the length
+  // of the gap (possibly zero) between the color table and the pixel data.
+  //
+  // If the gap is negative the file must be malformed (e.g. mH.mDataOffset
+  // points into the middle of the color palette instead of past the end) and
+  // we give up.
+  if (mPreGapLength > mH.mDataOffset) {
+    return Transition::TerminateFailure();
+  }
+
+  uint32_t gapLength = mH.mDataOffset - mPreGapLength;
+  return Transition::ToUnbuffered(State::AFTER_GAP, State::GAP, gapLength);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::SkipGap()
+{
+  return Transition::ContinueUnbuffered(State::GAP);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::AfterGap()
+{
+  // If there are no pixels we can stop.
+  //
+  // XXX: normally, if there are no pixels we will have stopped decoding before
+  // now, outside of this decoder. However, if the BMP is within an ICO file,
+  // it's possible that the ICO claimed the image had a non-zero size while the
+  // BMP claims otherwise. This test is to catch that awkward case. If we ever
+  // come up with a more general solution to this ICO-and-BMP-disagree-on-size
+  // problem, this test can be removed.
+  if (mH.mWidth == 0 || mH.mHeight == 0) {
+    return Transition::TerminateSuccess();
+  }
+
+  bool hasRLE = mH.mCompression == Compression::RLE8 ||
+                mH.mCompression == Compression::RLE4;
+  return hasRLE
+       ? Transition::To(State::RLE_SEGMENT, RLE::SEGMENT_LENGTH)
+       : Transition::To(State::PIXEL_ROW, mPixelRowSize);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadPixelRow(const char* aData)
+{
+  MOZ_ASSERT(mCurrentRow > 0);
+  MOZ_ASSERT(mCurrentPos == 0);
+
+  const uint8_t* src = reinterpret_cast<const uint8_t*>(aData);
+  uint32_t* dst = RowBuffer();
+  uint32_t lpos = mH.mWidth;
+  switch (mH.mBpp) {
+    case 1:
+      while (lpos > 0) {
+        int8_t bit;
+        uint8_t idx;
+        for (bit = 7; bit >= 0 && lpos > 0; bit--) {
+          idx = (*src >> bit) & 1;
+          SetPixel(dst, idx, mColors);
+          --lpos;
+        }
+        ++src;
+      }
+      break;
+
+    case 4:
+      while (lpos > 0) {
+        Set4BitPixel(dst, *src, lpos, mColors);
+        ++src;
+      }
+      break;
+
+    case 8:
+      while (lpos > 0) {
+        SetPixel(dst, *src, mColors);
+        --lpos;
+        ++src;
+      }
+      break;
+
+    case 16:
+      if (mBitFields.IsR5G5B5()) {
+        // Specialize this common case.
+        while (lpos > 0) {
+          uint16_t val = LittleEndian::readUint16(src);
+          SetPixel(dst, mBitFields.mRed.Get5(val),
+                        mBitFields.mGreen.Get5(val),
+                        mBitFields.mBlue.Get5(val));
+          --lpos;
+          src += 2;
+        }
+      } else {
+        bool anyHasAlpha = false;
+        while (lpos > 0) {
+          uint16_t val = LittleEndian::readUint16(src);
+          SetPixel(dst, mBitFields.mRed.Get(val),
+                        mBitFields.mGreen.Get(val),
+                        mBitFields.mBlue.Get(val),
+                        mBitFields.mAlpha.GetAlpha(val, anyHasAlpha));
+          --lpos;
+          src += 2;
+        }
+        if (anyHasAlpha) {
+          MOZ_ASSERT(mMayHaveTransparency);
+          mDoesHaveTransparency = true;
+        }
+      }
+      break;
+
+    case 24:
+      while (lpos > 0) {
+        SetPixel(dst, src[2], src[1], src[0]);
+        --lpos;
+        src += 3;
+      }
+      break;
+
+    case 32:
+      if (mH.mCompression == Compression::RGB && mIsWithinICO &&
+          mH.mBpp == 32) {
+        // This is a special case only used for 32bpp WinBMPv3-ICO files, which
+        // could be in either 0RGB or ARGB format. We start by assuming it's
+        // an 0RGB image. If we hit a non-zero alpha value, then we know it's
+        // actually an ARGB image, and change tack accordingly.
+        // (Note: a fully-transparent ARGB image is indistinguishable from a
+        // 0RGB image, and we will render such an image as a 0RGB image, i.e.
+        // opaquely. This is unlikely to be a problem in practice.)
+        while (lpos > 0) {
+          if (!mDoesHaveTransparency && src[3] != 0) {
+            // Up until now this looked like an 0RGB image, but we now know
+            // it's actually an ARGB image. Which means every pixel we've seen
+            // so far has been fully transparent. So we go back and redo them.
+
+            // Tell the Downscaler to go back to the start.
+            if (mDownscaler) {
+              mDownscaler->ResetForNextProgressivePass();
+            }
+
+            // Redo the complete rows we've already done.
+            MOZ_ASSERT(mCurrentPos == 0);
+            int32_t currentRow = mCurrentRow;
+            mCurrentRow = AbsoluteHeight();
+            while (mCurrentRow > currentRow) {
+              dst = RowBuffer();
+              for (int32_t i = 0; i < mH.mWidth; i++) {
+                SetPixel(dst, 0, 0, 0, 0);
+              }
+              FinishRow();
+            }
+
+            // Redo the part of this row we've already done.
+            dst = RowBuffer();
+            int32_t n = mH.mWidth - lpos;
+            for (int32_t i = 0; i < n; i++) {
+              SetPixel(dst, 0, 0, 0, 0);
+            }
+
+            MOZ_ASSERT(mMayHaveTransparency);
+            mDoesHaveTransparency = true;
+          }
+
+          // If mDoesHaveTransparency is false, treat this as an 0RGB image.
+          // Otherwise, treat this as an ARGB image.
+          SetPixel(dst, src[2], src[1], src[0],
+                   mDoesHaveTransparency ? src[3] : 0xff);
+          src += 4;
+          --lpos;
+        }
+      } else if (mBitFields.IsR8G8B8()) {
+        // Specialize this common case.
+        while (lpos > 0) {
+          uint32_t val = LittleEndian::readUint32(src);
+          SetPixel(dst, mBitFields.mRed.Get8(val),
+                        mBitFields.mGreen.Get8(val),
+                        mBitFields.mBlue.Get8(val));
+          --lpos;
+          src += 4;
+        }
+      } else {
+        bool anyHasAlpha = false;
+        while (lpos > 0) {
+          uint32_t val = LittleEndian::readUint32(src);
+          SetPixel(dst, mBitFields.mRed.Get(val),
+                        mBitFields.mGreen.Get(val),
+                        mBitFields.mBlue.Get(val),
+                        mBitFields.mAlpha.GetAlpha(val, anyHasAlpha));
+          --lpos;
+          src += 4;
+        }
+        if (anyHasAlpha) {
+          MOZ_ASSERT(mMayHaveTransparency);
+          mDoesHaveTransparency = true;
+        }
+      }
+      break;
+
+    default:
+      MOZ_CRASH("Unsupported color depth; earlier check didn't catch it?");
+  }
+
+  FinishRow();
+  return mCurrentRow == 0
+       ? Transition::TerminateSuccess()
+       : Transition::To(State::PIXEL_ROW, mPixelRowSize);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadRLESegment(const char* aData)
+{
+  if (mCurrentRow == 0) {
+    return Transition::TerminateSuccess();
+  }
+
+  uint8_t byte1 = uint8_t(aData[0]);
+  uint8_t byte2 = uint8_t(aData[1]);
+
+  if (byte1 != RLE::ESCAPE) {
+    // Encoded mode consists of two bytes: byte1 specifies the number of
+    // consecutive pixels to be drawn using the color index contained in
+    // byte2.
+    //
+    // Work around bitmaps that specify too many pixels.
+    uint32_t pixelsNeeded =
+      std::min<uint32_t>(mH.mWidth - mCurrentPos, byte1);
+    if (pixelsNeeded) {
+      uint32_t* dst = RowBuffer();
+      mCurrentPos += pixelsNeeded;
+      if (mH.mCompression == Compression::RLE8) {
+        do {
+          SetPixel(dst, byte2, mColors);
+          pixelsNeeded --;
+        } while (pixelsNeeded);
+      } else {
+        do {
+          Set4BitPixel(dst, byte2, pixelsNeeded, mColors);
+        } while (pixelsNeeded);
+      }
+    }
+    return Transition::To(State::RLE_SEGMENT, RLE::SEGMENT_LENGTH);
+  }
+
+  if (byte2 == RLE::ESCAPE_EOL) {
+    mCurrentPos = 0;
+    FinishRow();
+    return mCurrentRow == 0
+         ? Transition::TerminateSuccess()
+         : Transition::To(State::RLE_SEGMENT, RLE::SEGMENT_LENGTH);
+  }
+
+  if (byte2 == RLE::ESCAPE_EOF) {
+    return Transition::TerminateSuccess();
+  }
+
+  if (byte2 == RLE::ESCAPE_DELTA) {
+    return Transition::To(State::RLE_DELTA, RLE::DELTA_LENGTH);
+  }
+
+  // Absolute mode. |byte2| gives the number of pixels. The length depends on
+  // whether it's 4-bit or 8-bit RLE. Also, the length must be even (and zero
+  // padding is used to achieve this when necessary).
+  MOZ_ASSERT(mAbsoluteModeNumPixels == 0);
+  mAbsoluteModeNumPixels = byte2;
+  uint32_t length = byte2;
+  if (mH.mCompression == Compression::RLE4) {
+    length = (length + 1) / 2;    // halve, rounding up
+  }
+  if (length & 1) {
+    length++;
+  }
+  return Transition::To(State::RLE_ABSOLUTE, length);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadRLEDelta(const char* aData)
+{
+  // Delta encoding makes it possible to skip pixels making part of the image
+  // transparent.
+  MOZ_ASSERT(mMayHaveTransparency);
+  mDoesHaveTransparency = true;
+
+  if (mDownscaler) {
+    // Clear the skipped pixels. (This clears to the end of the row,
+    // which is perfect if there's a Y delta and harmless if not).
+    mDownscaler->ClearRestOfRow(/* aStartingAtCol = */ mCurrentPos);
+  }
+
+  // Handle the XDelta.
+  mCurrentPos += uint8_t(aData[0]);
+  if (mCurrentPos > mH.mWidth) {
+    mCurrentPos = mH.mWidth;
+  }
+
+  // Handle the Y Delta.
+  int32_t yDelta = std::min<int32_t>(uint8_t(aData[1]), mCurrentRow);
+  mCurrentRow -= yDelta;
+
+  if (mDownscaler && yDelta > 0) {
+    // Commit the current row (the first of the skipped rows).
+    mDownscaler->CommitRow();
+
+    // Clear and commit the remaining skipped rows.
+    for (int32_t line = 1; line < yDelta; line++) {
+      mDownscaler->ClearRow();
+      mDownscaler->CommitRow();
+    }
+  }
+
+  return mCurrentRow == 0
+       ? Transition::TerminateSuccess()
+       : Transition::To(State::RLE_SEGMENT, RLE::SEGMENT_LENGTH);
+}
+
+LexerTransition<nsBMPDecoder::State>
+nsBMPDecoder::ReadRLEAbsolute(const char* aData, size_t aLength)
+{
+  uint32_t n = mAbsoluteModeNumPixels;
+  mAbsoluteModeNumPixels = 0;
+
+  if (mCurrentPos + n > uint32_t(mH.mWidth)) {
+    // Bad data. Stop decoding; at least part of the image may have been
+    // decoded.
+    return Transition::TerminateSuccess();
+  }
+
+  // In absolute mode, n represents the number of pixels that follow, each of
+  // which contains the color index of a single pixel.
+  uint32_t* dst = RowBuffer();
+  uint32_t iSrc = 0;
+  uint32_t* oldPos = dst;
+  if (mH.mCompression == Compression::RLE8) {
+    while (n > 0) {
+      SetPixel(dst, aData[iSrc], mColors);
+      n--;
+      iSrc++;
+    }
+  } else {
+    while (n > 0) {
+      Set4BitPixel(dst, aData[iSrc], n, mColors);
+      iSrc++;
+    }
+  }
+  mCurrentPos += dst - oldPos;
+
+  // We should read all the data (unless the last byte is zero padding).
+  MOZ_ASSERT(iSrc == aLength - 1 || iSrc == aLength);
+
+  return Transition::To(State::RLE_SEGMENT, RLE::SEGMENT_LENGTH);
+}
+
+} // namespace image
+} // namespace mozilla