libwebp: update to 0.4.2-rc2

third_party/libwebp/enc/analysis.c

 // Copyright 2011 Google Inc. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the COPYING file in the root of the source
 // tree. An additional intellectual property rights grant can be found
 // in the file PATENTS. All contributing project authors may
 // be found in the AUTHORS file in the root of the source tree.
 // -----------------------------------------------------------------------------
 //
 // Macroblock analysis
@@ skipping 123 matching lines @@
   for (i = 0; i <= MAX_COEFF_THRESH; ++i) {
     out->distribution[i] += in->distribution[i];
   }
 }
 
 //------------------------------------------------------------------------------
 // Simplified k-Means, to assign Nb segments based on alpha-histogram
 
 static void AssignSegments(VP8Encoder* const enc,
                            const int alphas[MAX_ALPHA + 1]) {
-  const int nb = enc->segment_hdr_.num_segments_;
+  // 'num_segments_' is previously validated and <= NUM_MB_SEGMENTS, but an
+  // explicit check is needed to avoid spurious warning about 'n + 1' exceeding
+  // array bounds of 'centers' with some compilers (noticed with gcc-4.9).
+  const int nb = (enc->segment_hdr_.num_segments_ < NUM_MB_SEGMENTS) ?
+                 enc->segment_hdr_.num_segments_ : NUM_MB_SEGMENTS;
   int centers[NUM_MB_SEGMENTS];
   int weighted_average = 0;
   int map[MAX_ALPHA + 1];
   int a, n, k;
   int min_a = 0, max_a = MAX_ALPHA, range_a;
   // 'int' type is ok for histo, and won't overflow
   int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
 
   assert(nb >= 1);
   assert(nb <= NUM_MB_SEGMENTS);
@@ skipping 330 matching lines @@
       enc->alpha_ = main_job.alpha / total_mb;
       enc->uv_alpha_ = main_job.uv_alpha / total_mb;
       AssignSegments(enc, main_job.alphas);
     }
   } else {   // Use only one default segment.
     ResetAllMBInfo(enc);
   }
   return ok;
 }