This logic, meant to detect any negative or too high value, fails
if the second parameter may also be negative, such as when video
dimensions are <= the size of one macroblock
---
 libavcodec/snow.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/snow.c b/libavcodec/snow.c
index 447289a..ed521a9 100644
--- a/libavcodec/snow.c
+++ b/libavcodec/snow.c
@@ -337,8 +337,8 @@ void ff_snow_pred_block(SnowContext *s, uint8_t *dst, 
uint8_t *tmp, int stride,
         sx += (mx>>4) - (HTAPS_MAX/2-1);
         sy += (my>>4) - (HTAPS_MAX/2-1);
         src += sx + sy*stride;
-        if(   (unsigned)sx >= w - b_w - (HTAPS_MAX-2)
-           || (unsigned)sy >= h - b_h - (HTAPS_MAX-2)){
+        if(   (unsigned)sx >= FFMAX(w - b_w - (HTAPS_MAX-2), 0)
+           || (unsigned)sy >= FFMAX(h - b_h - (HTAPS_MAX-2), 0)){
             s->dsp.emulated_edge_mc(tmp + MB_SIZE, src, stride, 
b_w+HTAPS_MAX-1, b_h+HTAPS_MAX-1, sx, sy, w, h);
             src= tmp + MB_SIZE;
         }
-- 
1.7.5.4

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