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Overflow of frame error accumulators.

This fixes an overflow problem in the frame error accumulators.

The overflow condition is extreme but did trigger when Frank B.
coded some high motion interlaced HD content.

The observed effect was a catastrophic  breakdown of the rate
control leading to massive undershoot and poor bit allocation.

All the error values should really be unsigned but I will look at this
separately.

Change-Id: I9745f5c5ca2783620426b66b568b2088b579151f

--- a/vp8/encoder/firstpass.c

+++ b/vp8/encoder/firstpass.c

@@ -560,8 +560,8 @@

     YV12_BUFFER_CONFIG *gld_yv12 = &cm->yv12_fb[cm->gld_fb_idx];

     int recon_y_stride = lst_yv12->y_stride;

     int recon_uv_stride = lst_yv12->uv_stride;

-    int intra_error = 0;

-    int coded_error = 0;

+    long long intra_error = 0;

+    long long coded_error = 0;

     int sum_mvr = 0, sum_mvc = 0;

     int sum_mvr_abs = 0, sum_mvc_abs = 0;

@@ -648,7 +648,7 @@

             this_error += intrapenalty;

             // Cumulative intra error total

-            intra_error += this_error;

+            intra_error += (long long)this_error;

             // Indicate default assumption of intra in the motion map

             *fp_motion_map_ptr = 0;

@@ -800,7 +800,7 @@

                 }

             }

-            coded_error += this_error;

+            coded_error += (long long)this_error;

             // adjust to the next column of macroblocks

             x->src.y_buffer += 16;

-- 

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