fix overflow in mc_block() patch by (Yartrebo )yartrebo earthlink net

Originally committed as revision 4132 to svn://svn.ffmpeg.org/ffmpeg/trunk

diff --git a/libavcodec/snow.c b/libavcodec/snow.c
index 7020b39..9cfddfa 100644 (file)
--- a/libavcodec/snow.c
+++ b/libavcodec/snow.c
@@ -2359,8 +2359,13 @@ START_TIMER
 
 //            if(b_w==16) am= 8*(a1+a2);
 
-            if(dx<8) tmp[x]= (32*a2*( 8-dx) +    am* dx    + 128)>>8;
-            else     tmp[x]= (   am*(16-dx) + 32*a3*(dx-8) + 128)>>8;
+            if(dx<8) am = (32*a2*( 8-dx) +    am* dx    + 128)>>8;
+            else     am = (   am*(16-dx) + 32*a3*(dx-8) + 128)>>8;
+            
+            /* FIXME Try increasing tmp buffer to 16 bits and not clipping here. Should give marginally better results. - Robert*/
+            if(am&(~255)) am= ~(am>>31);
+            
+            tmp[x] = am;
 
 /*            if     (dx< 4) tmp[x + y*stride]= (16*a1*( 4-dx) +    aL* dx     + 32)>>6;
             else if(dx< 8) tmp[x + y*stride]= (   aL*( 8-dx) +    am*(dx- 4) + 32)>>6;
@@ -2387,9 +2392,12 @@ START_TIMER
             
 //            if(b_w==16) am= 8*(a1+a2);
 
-            if(dy<8) dst[x]= (32*a2*( 8-dy) +    am* dy    + 128)>>8;
-            else     dst[x]= (   am*(16-dy) + 32*a3*(dy-8) + 128)>>8;
+            if(dy<8) am =  (32*a2*( 8-dy) +    am* dy    + 128)>>8;
+            else     am = (   am*(16-dy) + 32*a3*(dy-8) + 128)>>8;
 
+            if(am&(~255)) am= ~(am>>31);
+            
+            dst[x] = am;
 /*            if     (dy< 4) tmp[x + y*stride]= (16*a1*( 4-dy) +    aL* dy     + 32)>>6;
             else if(dy< 8) tmp[x + y*stride]= (   aL*( 8-dy) +    am*(dy- 4) + 32)>>6;
             else if(dy<12) tmp[x + y*stride]= (   am*(12-dy) +    aR*(dy- 8) + 32)>>6;

diff --git a/tests/ffmpeg.regression.ref b/tests/ffmpeg.regression.ref
index 1f920a9..f3809b0 100644 (file)
--- a/tests/ffmpeg.regression.ref
+++ b/tests/ffmpeg.regression.ref
@@ -119,12 +119,12 @@ a7ef4746f27be309138c188e327d3ebe *./data/a-ffv1.avi
 2653642 ./data/a-ffv1.avi
 799d3db687f6cdd7a837ec156efc171f *./data/out.yuv
 stddev:  0.00 PSNR:99.99 bytes:7602176
-24c1fcbcdb08052359679700056ef4e5 *./data/a-snow.avi
-1267526 ./data/a-snow.avi
-575fdd879119902a8289c825c2389dca *./data/out.yuv
-stddev:  2.96 PSNR:38.67 bytes:7602176
-0c570833b736a8d4c8c428bf6e82272f *./data/a-snow53.avi
-3537490 ./data/a-snow53.avi
+0c447fd23c33ef06b09ecae5e1959185 *./data/a-snow.avi
+1263028 ./data/a-snow.avi
+d2d86a95325f5c166fc07e5670b2adb6 *./data/out.yuv
+stddev:  2.97 PSNR:38.67 bytes:7602176
+de8eac1454746a37eae0b1ff88c0f849 *./data/a-snow53.avi
+3535414 ./data/a-snow53.avi
 799d3db687f6cdd7a837ec156efc171f *./data/out.yuv
 stddev:  0.00 PSNR:99.99 bytes:7602176
 b5b6275f58f012de73644bbaa9080097 *./data/a-svq1.mov