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diff --git a/gfx/thebes/gfxAlphaRecovery.h b/gfx/thebes/gfxAlphaRecovery.h
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+++ b/gfx/thebes/gfxAlphaRecovery.h
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+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * 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/. */
+
+#ifndef _GFXALPHARECOVERY_H_
+#define _GFXALPHARECOVERY_H_
+
+#include "mozilla/SSE.h"
+#include "gfxTypes.h"
+#include "mozilla/gfx/Rect.h"
+
+class gfxImageSurface;
+
+class gfxAlphaRecovery {
+public:
+    /**
+     * Some SIMD fast-paths only can be taken if the relative
+     * byte-alignment of images' pointers and strides meets certain
+     * criteria.  Aligning image pointers and strides by
+     * |GoodAlignmentLog2()| below will ensure that fast-paths aren't
+     * skipped because of misalignment.  Fast-paths may still be taken
+     * even if GoodAlignmentLog2() is not met, in some conditions.
+     */
+    static uint32_t GoodAlignmentLog2() { return 4; /* for SSE2 */ }
+
+    /* Given two surfaces of equal size with the same rendering, one onto a
+     * black background and the other onto white, recovers alpha values from
+     * the difference and sets the alpha values on the black surface.
+     * The surfaces must have format RGB24 or ARGB32.
+     * Returns true on success.
+     */
+    static bool RecoverAlpha (gfxImageSurface *blackSurface,
+                                const gfxImageSurface *whiteSurface);
+
+#ifdef MOZILLA_MAY_SUPPORT_SSE2
+    /* This does the same as the previous function, but uses SSE2
+     * optimizations. Usually this should not be called directly.  Be sure to
+     * check mozilla::supports_sse2() before calling this function.
+     */
+    static bool RecoverAlphaSSE2 (gfxImageSurface *blackSurface,
+                                    const gfxImageSurface *whiteSurface);
+
+    /**
+     * A common use-case for alpha recovery is to paint into a
+     * temporary "white image", then paint onto a subrect of the
+     * surface, the "black image", into which alpha-recovered pixels
+     * are eventually to be written.  This function returns a rect
+     * aligned so that recovering alpha for that rect will hit SIMD
+     * fast-paths, if possible.  It's not always possible to align
+     * |aRect| so that fast-paths will be taken.
+     *
+     * The returned rect is always a superset of |aRect|.
+     */
+    static mozilla::gfx::IntRect AlignRectForSubimageRecovery(const mozilla::gfx::IntRect& aRect,
+                                                              gfxImageSurface* aSurface);
+#else
+    static mozilla::gfx::IntRect AlignRectForSubimageRecovery(const mozilla::gfx::IntRect& aRect,
+                                                              gfxImageSurface*)
+    { return aRect; }
+#endif
+
+    /** from cairo-xlib-utils.c, modified */
+    /**
+     * Given the RGB data for two image surfaces, one a source image composited
+     * with OVER onto a black background, and one a source image composited with 
+     * OVER onto a white background, reconstruct the original image data into
+     * black_data.
+     *
+     * Consider a single color channel and a given pixel. Suppose the original
+     * premultiplied color value was C and the alpha value was A. Let the final
+     * on-black color be B and the final on-white color be W. All values range
+     * over 0-255.
+     *
+     * Then B=C and W=(255*(255 - A) + C*255)/255. Solving for A, we get
+     * A=255 - (W - C). Therefore it suffices to leave the black_data color
+     * data alone and set the alpha values using that simple formula. It shouldn't
+     * matter what color channel we pick for the alpha computation, but we'll
+     * pick green because if we went through a color channel downsample the green
+     * bits are likely to be the most accurate.
+     *
+     * This function needs to be in the header file since it's used by both
+     * gfxRecoverAlpha.cpp and gfxRecoverAlphaSSE2.cpp.
+     */
+
+    static inline uint32_t
+    RecoverPixel(uint32_t black, uint32_t white)
+    {
+        const uint32_t GREEN_MASK = 0x0000FF00;
+        const uint32_t ALPHA_MASK = 0xFF000000;
+
+        /* |diff| here is larger when the source image pixel is more transparent.
+           If both renderings are from the same source image composited with OVER,
+           then the color values on white will always be greater than those on
+           black, so |diff| would not overflow.  However, overflow may happen, for
+           example, when a plugin plays a video and the image is rapidly changing.
+           If there is overflow, then behave as if we limit to the difference to
+           >= 0, which will make the rendering opaque.  (Without this overflow
+           will make the rendering transparent.) */
+        uint32_t diff = (white & GREEN_MASK) - (black & GREEN_MASK);
+        /* |diff| is 0xFFFFxx00 on overflow and 0x0000xx00 otherwise, so use this
+            to limit the transparency. */
+        uint32_t limit = diff & ALPHA_MASK;
+        /* The alpha bits of the result */
+        uint32_t alpha = (ALPHA_MASK - (diff << 16)) | limit;
+
+        return alpha | (black & ~ALPHA_MASK);
+    }
+};
+
+#endif /* _GFXALPHARECOVERY_H_ */