vc1: fix out of array reads in vc1_inv_trans_4x8_c()

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vc1dsp.c

@@ -421,7 +421,6 @@ static void vc1_inv_trans_4x8_c(uint8_t *dest, int linesize, DCTELEM *block)
     int i;
     register int t1,t2,t3,t4,t5,t6,t7,t8;
     DCTELEM *src, *dst;
-    const uint8_t *cm = ff_cropTbl + MAX_NEG_CROP;
 
     src = block;
     dst = block;
@@ -457,14 +456,14 @@ static void vc1_inv_trans_4x8_c(uint8_t *dest, int linesize, DCTELEM *block)
         t3 =  9 * src[ 8] - 16 * src[24] +  4 * src[40] + 15 * src[56];
         t4 =  4 * src[ 8] -  9 * src[24] + 15 * src[40] - 16 * src[56];
 
-        dest[0*linesize] = cm[dest[0*linesize] + ((t5 + t1) >> 7)];
-        dest[1*linesize] = cm[dest[1*linesize] + ((t6 + t2) >> 7)];
-        dest[2*linesize] = cm[dest[2*linesize] + ((t7 + t3) >> 7)];
-        dest[3*linesize] = cm[dest[3*linesize] + ((t8 + t4) >> 7)];
-        dest[4*linesize] = cm[dest[4*linesize] + ((t8 - t4 + 1) >> 7)];
-        dest[5*linesize] = cm[dest[5*linesize] + ((t7 - t3 + 1) >> 7)];
-        dest[6*linesize] = cm[dest[6*linesize] + ((t6 - t2 + 1) >> 7)];
-        dest[7*linesize] = cm[dest[7*linesize] + ((t5 - t1 + 1) >> 7)];
+        dest[0*linesize] = av_clip_uint8(dest[0*linesize] + ((t5 + t1) >> 7));
+        dest[1*linesize] = av_clip_uint8(dest[1*linesize] + ((t6 + t2) >> 7));
+        dest[2*linesize] = av_clip_uint8(dest[2*linesize] + ((t7 + t3) >> 7));
+        dest[3*linesize] = av_clip_uint8(dest[3*linesize] + ((t8 + t4) >> 7));
+        dest[4*linesize] = av_clip_uint8(dest[4*linesize] + ((t8 - t4 + 1) >> 7));
+        dest[5*linesize] = av_clip_uint8(dest[5*linesize] + ((t7 - t3 + 1) >> 7));
+        dest[6*linesize] = av_clip_uint8(dest[6*linesize] + ((t6 - t2 + 1) >> 7));
+        dest[7*linesize] = av_clip_uint8(dest[7*linesize] + ((t5 - t1 + 1) >> 7));
 
         src ++;
         dest++;