libwebp: update snapshot to v0.3.0-rc6

third_party/libwebp/dsp/lossless.h

 // Copyright 2012 Google Inc. All Rights Reserved.
 //
 // This code is licensed under the same terms as WebM:
 //  Software License Agreement:  http://www.webmproject.org/license/software/
 //  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
 // -----------------------------------------------------------------------------
 //
 // Image transforms and color space conversion methods for lossless decoder.
 //
 // Authors: Vikas Arora (vikaas.arora@gmail.com)
@@ skipping 41 matching lines @@
 
 //------------------------------------------------------------------------------
 // Misc methods.
 
 // Computes sampled size of 'size' when sampling using 'sampling bits'.
 static WEBP_INLINE uint32_t VP8LSubSampleSize(uint32_t size,
                                               uint32_t sampling_bits) {
   return (size + (1 << sampling_bits) - 1) >> sampling_bits;
 }
 
-// Faster logarithm for integers, with the property of log2(0) == 0.
-float VP8LFastLog2(int v);
+// Faster logarithm for integers. Small values use a look-up table.
+#define LOG_LOOKUP_IDX_MAX 256
+extern const float kLog2Table[LOG_LOOKUP_IDX_MAX];
+extern const float kSLog2Table[LOG_LOOKUP_IDX_MAX];
+extern float VP8LFastLog2Slow(int v);
+extern float VP8LFastSLog2Slow(int v);
+static WEBP_INLINE float VP8LFastLog2(int v) {
+  return (v < LOG_LOOKUP_IDX_MAX) ? kLog2Table[v] : VP8LFastLog2Slow(v);
+}
 // Fast calculation of v * log2(v) for integer input.
-static WEBP_INLINE float VP8LFastSLog2(int v) { return VP8LFastLog2(v) * v; }
+static WEBP_INLINE float VP8LFastSLog2(int v) {
+  return (v < LOG_LOOKUP_IDX_MAX) ? kSLog2Table[v] : VP8LFastSLog2Slow(v);
+}
+
 
 // In-place difference of each component with mod 256.
 static WEBP_INLINE uint32_t VP8LSubPixels(uint32_t a, uint32_t b) {
   const uint32_t alpha_and_green =
       0x00ff00ffu + (a & 0xff00ff00u) - (b & 0xff00ff00u);
   const uint32_t red_and_blue =
       0xff00ff00u + (a & 0x00ff00ffu) - (b & 0x00ff00ffu);
   return (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
 }
 
 //------------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)
 }    // extern "C"
 #endif
 
 #endif  // WEBP_DSP_LOSSLESS_H_