libwebp: update snapshot to v0.3.0-rc6

third_party/libwebp/dsp/yuv.h

Index: third_party/libwebp/dsp/yuv.h
diff --git a/third_party/libwebp/dsp/yuv.h b/third_party/libwebp/dsp/yuv.h
index 22cb25963cac91c2a74d359f33cfadb185192c1f..126404b667768b81da4cc55aff75ce91e32e2ed1 100644
--- a/third_party/libwebp/dsp/yuv.h
+++ b/third_party/libwebp/dsp/yuv.h
@@ -7,6 +7,26 @@
 //
 // inline YUV<->RGB conversion function
 //
+// The exact naming is Y'CbCr, following the ITU-R BT.601 standard.
+// More information at: http://en.wikipedia.org/wiki/YCbCr
+// Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16
+// U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128
+// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128
+// We use 16bit fixed point operations for RGB->YUV conversion.
+//
+// For the Y'CbCr to RGB conversion, the BT.601 specification reads:
+//   R = 1.164 * (Y-16) + 1.596 * (V-128)
+//   G = 1.164 * (Y-16) - 0.813 * (V-128) - 0.391 * (U-128)
+//   B = 1.164 * (Y-16)                   + 2.018 * (U-128)
+// where Y is in the [16,235] range, and U/V in the [16,240] range.
+// In the table-lookup version (WEBP_YUV_USE_TABLE), the common factor
+// "1.164 * (Y-16)" can be handled as an offset in the VP8kClip[] table.
+// So in this case the formulae should be read as:
+//   R = 1.164 * [Y + 1.371 * (V-128)                  ] - 18.624
+//   G = 1.164 * [Y - 0.698 * (V-128) - 0.336 * (U-128)] - 18.624
+//   B = 1.164 * [Y                   + 1.733 * (U-128)] - 18.624
+// once factorized. Here too, 16bit fixed precision is used.
+//
 // Author: Skal (pascal.massimino@gmail.com)
 
 #ifndef WEBP_DSP_YUV_H_
@@ -14,6 +34,19 @@
 
 #include "../dec/decode_vp8.h"
 
+// Define the following to use the LUT-based code:
+#define WEBP_YUV_USE_TABLE
+
+#if defined(WEBP_EXPERIMENTAL_FEATURES)
+// Do NOT activate this feature for real compression. This is only experimental!
+// This flag is for comparison purpose against JPEG's "YUVj" natural colorspace.
+// This colorspace is close to Rec.601's Y'CbCr model with the notable
+// difference of allowing larger range for luma/chroma.
+// See http://en.wikipedia.org/wiki/YCbCr#JPEG_conversion paragraph, and its
+// difference with http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion
+// #define USE_YUVj
+#endif
+
 //------------------------------------------------------------------------------
 // YUV -> RGB conversion
 
@@ -22,9 +55,14 @@ extern "C" {
 #endif
 
 enum { YUV_FIX = 16,                // fixed-point precision
+       YUV_HALF = 1 << (YUV_FIX - 1),
+       YUV_MASK = (256 << YUV_FIX) - 1,
        YUV_RANGE_MIN = -227,        // min value of r/g/b output
        YUV_RANGE_MAX = 256 + 226    // max value of r/g/b output
 };
+
+#ifdef WEBP_YUV_USE_TABLE
+
 extern int16_t VP8kVToR[256], VP8kUToB[256];
 extern int32_t VP8kVToG[256], VP8kUToG[256];
 extern uint8_t VP8kClip[YUV_RANGE_MAX - YUV_RANGE_MIN];
@@ -40,21 +78,32 @@ static WEBP_INLINE void VP8YuvToRgb(uint8_t y, uint8_t u, uint8_t v,
   rgb[2] = VP8kClip[y + b_off - YUV_RANGE_MIN];
 }
 
-static WEBP_INLINE void VP8YuvToRgb565(uint8_t y, uint8_t u, uint8_t v,
-                                       uint8_t* const rgb) {
+static WEBP_INLINE void VP8YuvToBgr(uint8_t y, uint8_t u, uint8_t v,
+                                    uint8_t* const bgr) {
   const int r_off = VP8kVToR[v];
   const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
   const int b_off = VP8kUToB[u];
-  rgb[0] = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) |
-            (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5));
-  rgb[1] = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) |
-            (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3));
+  bgr[0] = VP8kClip[y + b_off - YUV_RANGE_MIN];
+  bgr[1] = VP8kClip[y + g_off - YUV_RANGE_MIN];
+  bgr[2] = VP8kClip[y + r_off - YUV_RANGE_MIN];
 }
 
-static WEBP_INLINE void VP8YuvToArgb(uint8_t y, uint8_t u, uint8_t v,
-                                     uint8_t* const argb) {
-  argb[0] = 0xff;
-  VP8YuvToRgb(y, u, v, argb + 1);
+static WEBP_INLINE void VP8YuvToRgb565(uint8_t y, uint8_t u, uint8_t v,
+                                       uint8_t* const rgb) {
+  const int r_off = VP8kVToR[v];
+  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
+  const int b_off = VP8kUToB[u];
+  const uint8_t rg = ((VP8kClip[y + r_off - YUV_RANGE_MIN] & 0xf8) |
+                      (VP8kClip[y + g_off - YUV_RANGE_MIN] >> 5));
+  const uint8_t gb = (((VP8kClip[y + g_off - YUV_RANGE_MIN] << 3) & 0xe0) |
+                      (VP8kClip[y + b_off - YUV_RANGE_MIN] >> 3));
+#ifdef WEBP_SWAP_16BIT_CSP
+  rgb[0] = gb;
+  rgb[1] = rg;
+#else
+  rgb[0] = rg;
+  rgb[1] = gb;
+#endif
 }
 
 static WEBP_INLINE void VP8YuvToRgba4444(uint8_t y, uint8_t u, uint8_t v,
@@ -62,20 +111,104 @@ static WEBP_INLINE void VP8YuvToRgba4444(uint8_t y, uint8_t u, uint8_t v,
   const int r_off = VP8kVToR[v];
   const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
   const int b_off = VP8kUToB[u];
-  // Don't update alpha (last 4 bits of argb[1])
-  argb[0] = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) |
-             VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]);
-  argb[1] = 0x0f | (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4);
+  const uint8_t rg = ((VP8kClip4Bits[y + r_off - YUV_RANGE_MIN] << 4) |
+                      VP8kClip4Bits[y + g_off - YUV_RANGE_MIN]);
+  const uint8_t ba = (VP8kClip4Bits[y + b_off - YUV_RANGE_MIN] << 4) | 0x0f;
+#ifdef WEBP_SWAP_16BIT_CSP
+  argb[0] = ba;
+  argb[1] = rg;
+#else
+  argb[0] = rg;
+  argb[1] = ba;
+#endif
+}
+
+#else   // Table-free version (slower on x86)
+
+// These constants are 16b fixed-point version of ITU-R BT.601 constants
+#define kYScale 76309      // 1.164 = 255 / 219
+#define kVToR   104597     // 1.596 = 255 / 112 * 0.701
+#define kUToG   25674      // 0.391 = 255 / 112 * 0.886 * 0.114 / 0.587
+#define kVToG   53278      // 0.813 = 255 / 112 * 0.701 * 0.299 / 0.587
+#define kUToB   132201     // 2.018 = 255 / 112 * 0.886
+#define kRCst (-kYScale * 16 - kVToR * 128 + YUV_HALF)
+#define kGCst (-kYScale * 16 + kUToG * 128 + kVToG * 128 + YUV_HALF)
+#define kBCst (-kYScale * 16 - kUToB * 128 + YUV_HALF)
+
+static WEBP_INLINE uint8_t VP8Clip8(int v) {
+  return ((v & ~YUV_MASK) == 0) ? (uint8_t)(v >> YUV_FIX)
+                                : (v < 0) ? 0u : 255u;
+}
+
+static WEBP_INLINE uint8_t VP8ClipN(int v, int N) {  // clip to N bits
+  return ((v & ~YUV_MASK) == 0) ? (uint8_t)(v >> (YUV_FIX + (8 - N)))
+                                : (v < 0) ? 0u : (255u >> (8 - N));
+}
+
+static WEBP_INLINE int VP8YUVToR(int y, int v) {
+  return kYScale * y + kVToR * v + kRCst;
+}
+
+static WEBP_INLINE int VP8YUVToG(int y, int u, int v) {
+  return kYScale * y - kUToG * u - kVToG * v + kGCst;
+}
+
+static WEBP_INLINE int VP8YUVToB(int y, int u) {
+  return kYScale * y  + kUToB * u + kBCst;
+}
+
+static WEBP_INLINE void VP8YuvToRgb(uint8_t y, uint8_t u, uint8_t v,
+                                    uint8_t* const rgb) {
+  rgb[0] = VP8Clip8(VP8YUVToR(y, v));
+  rgb[1] = VP8Clip8(VP8YUVToG(y, u, v));
+  rgb[2] = VP8Clip8(VP8YUVToB(y, u));
 }
 
 static WEBP_INLINE void VP8YuvToBgr(uint8_t y, uint8_t u, uint8_t v,
                                     uint8_t* const bgr) {
-  const int r_off = VP8kVToR[v];
-  const int g_off = (VP8kVToG[v] + VP8kUToG[u]) >> YUV_FIX;
-  const int b_off = VP8kUToB[u];
-  bgr[0] = VP8kClip[y + b_off - YUV_RANGE_MIN];
-  bgr[1] = VP8kClip[y + g_off - YUV_RANGE_MIN];
-  bgr[2] = VP8kClip[y + r_off - YUV_RANGE_MIN];
+  bgr[0] = VP8Clip8(VP8YUVToB(y, u));
+  bgr[1] = VP8Clip8(VP8YUVToG(y, u, v));
+  bgr[2] = VP8Clip8(VP8YUVToR(y, v));
+}
+
+static WEBP_INLINE void VP8YuvToRgb565(uint8_t y, uint8_t u, uint8_t v,
+                                       uint8_t* const rgb) {
+  const int r = VP8Clip8(VP8YUVToR(y, u));
+  const int g = VP8ClipN(VP8YUVToG(y, u, v), 6);
+  const int b = VP8ClipN(VP8YUVToB(y, v), 5);
+  const uint8_t rg = (r & 0xf8) | (g >> 3);
+  const uint8_t gb = (g << 5) | b;
+#ifdef WEBP_SWAP_16BIT_CSP
+  rgb[0] = gb;
+  rgb[1] = rg;
+#else
+  rgb[0] = rg;
+  rgb[1] = gb;
+#endif
+}
+
+static WEBP_INLINE void VP8YuvToRgba4444(uint8_t y, uint8_t u, uint8_t v,
+                                         uint8_t* const argb) {
+  const int r = VP8Clip8(VP8YUVToR(y, u));
+  const int g = VP8ClipN(VP8YUVToG(y, u, v), 4);
+  const int b = VP8Clip8(VP8YUVToB(y, v));
+  const uint8_t rg = (r & 0xf0) | g;
+  const uint8_t ba = b | 0x0f;   // overwrite the lower 4 bits
+#ifdef WEBP_SWAP_16BIT_CSP
+  argb[0] = ba;
+  argb[1] = rg;
+#else
+  argb[0] = rg;
+  argb[1] = ba;
+#endif
+}
+
+#endif  // WEBP_YUV_USE_TABLE
+
+static WEBP_INLINE void VP8YuvToArgb(uint8_t y, uint8_t u, uint8_t v,
+                                     uint8_t* const argb) {
+  argb[0] = 0xff;
+  VP8YuvToRgb(y, u, v, argb + 1);
 }
 
 static WEBP_INLINE void VP8YuvToBgra(uint8_t y, uint8_t u, uint8_t v,
@@ -90,28 +223,19 @@ static WEBP_INLINE void VP8YuvToRgba(uint8_t y, uint8_t u, uint8_t v,
   rgba[3] = 0xff;
 }
 
-static WEBP_INLINE uint32_t VP8Clip4Bits(uint8_t c) {
-  const uint32_t v = (c + 8) >> 4;
-  return (v > 15) ? 15 : v;
-}
-
 // Must be called before everything, to initialize the tables.
 void VP8YUVInit(void);
 
 //------------------------------------------------------------------------------
 // RGB -> YUV conversion
-// The exact naming is Y'CbCr, following the ITU-R BT.601 standard.
-// More information at: http://en.wikipedia.org/wiki/YCbCr
-// Y = 0.2569 * R + 0.5044 * G + 0.0979 * B + 16
-// U = -0.1483 * R - 0.2911 * G + 0.4394 * B + 128
-// V = 0.4394 * R - 0.3679 * G - 0.0715 * B + 128
-// We use 16bit fixed point operations.
 
 static WEBP_INLINE int VP8ClipUV(int v) {
-   v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2);
-   return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255;
+  v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2);
+  return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255;
 }
 
+#ifndef USE_YUVj
+
 static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
   const int kRound = (1 << (YUV_FIX - 1)) + (16 << YUV_FIX);
   const int luma = 16839 * r + 33059 * g + 6420 * b;
@@ -119,13 +243,38 @@ static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
 }
 
 static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
-  return VP8ClipUV(-9719 * r - 19081 * g + 28800 * b);
+  const int u = -9719 * r - 19081 * g + 28800 * b;
+  return VP8ClipUV(u);
+}
+
+static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
+  const int v = +28800 * r - 24116 * g - 4684 * b;
+  return VP8ClipUV(v);
+}
+
+#else
+
+// This JPEG-YUV colorspace, only for comparison!
+// These are also 16-bit precision coefficients from Rec.601, but with full
+// [0..255] output range.
+static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
+  const int kRound = (1 << (YUV_FIX - 1));
+  const int luma = 19595 * r + 38470 * g + 7471 * b;
+  return (luma + kRound) >> YUV_FIX;  // no need to clip
+}
+
+static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
+  const int u = -11058 * r - 21710 * g + 32768 * b;
+  return VP8ClipUV(u);
 }
 
 static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
-  return VP8ClipUV(+28800 * r - 24116 * g - 4684 * b);
+  const int v = 32768 * r - 27439 * g - 5329 * b;
+  return VP8ClipUV(v);
 }
 
+#endif    // USE_YUVj
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }    // extern "C"
 #endif