Add utils to better quantize grayscale values to three bit indices while

src/utils/SkTextureCompressor_LATC.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTextureCompressor_LATC.h"
 #include "SkTextureCompressor_Blitter.h"
+#include "SkTextureCompressor_Utils.h"
 
 #include "SkBlitter.h"
 #include "SkEndian.h"
 
 // Compression options. In general, the slow version is much more accurate, but
 // much slower. The fast option is much faster, but much less accurate. YMMV.
 #define COMPRESS_LATC_SLOW 0
 #define COMPRESS_LATC_FAST 1
 
 ////////////////////////////////////////////////////////////////////////////////
@@ skipping 302 matching lines @@
     // Since the palette is 
     // 255, 0, 219, 182, 146, 109, 73, 36
     // we need to map the high three bits of each byte in the integer
     // from
     // 0 1 2 3 4 5 6 7
     // to
     // 1 7 6 5 4 3 2 0
     //
     // This first operation takes the mapping from
     // 0 1 2 3 4 5 6 7  -->  7 6 5 4 3 2 1 0
-    x = 0x07070707 - ((x >> 5) & 0x07070707);
+    x = 0x07070707 - SkTextureCompressor::ConvertToThreeBitIndex(x);
 
     // mask is 1 if index is non-zero
     const uint32_t mask = (x | (x >> 1) | (x >> 2)) & 0x01010101;
 
     // add mask:
     // 7 6 5 4 3 2 1 0 --> 8 7 6 5 4 3 2 0
     x = (x + mask);
 
     // Handle overflow:
     // 8 7 6 5 4 3 2 0 --> 9 7 6 5 4 3 2 0
@@ skipping 166 matching lines @@
     for (int j = 0; j < height; j += 4) {
         for (int i = 0; i < width; i += 4) {
             decompress_latc_block(dst + i, dstRowBytes, src);
             src += 8;
         }
         dst += 4 * dstRowBytes;
     }
 }
 
 }  // SkTextureCompressor