mpc: pad mpc_CC/SCF[] tables to allow for negative indices.

MPC8 allows indices of mpc_CC up to -1, and mpc_SCF up to -6, thus pad
the tables by that much on the left end.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/mpc.c

@@ -78,13 +78,13 @@ void ff_mpc_dequantize_and_synth(MPCContext * c, int maxband, void *data, int ch
         for(ch = 0; ch < 2; ch++){
             if(bands[i].res[ch]){
                 j = 0;
-                mul = mpc_CC[bands[i].res[ch]] * mpc_SCF[bands[i].scf_idx[ch][0]];
+                mul = mpc_CC[bands[i].res[ch] + 1] * mpc_SCF[bands[i].scf_idx[ch][0]+6];
                 for(; j < 12; j++)
                     c->sb_samples[ch][j][i] = mul * c->Q[ch][j + off];
-                mul = mpc_CC[bands[i].res[ch]] * mpc_SCF[bands[i].scf_idx[ch][1]];
+                mul = mpc_CC[bands[i].res[ch] + 1] * mpc_SCF[bands[i].scf_idx[ch][1]+6];
                 for(; j < 24; j++)
                     c->sb_samples[ch][j][i] = mul * c->Q[ch][j + off];
-                mul = mpc_CC[bands[i].res[ch]] * mpc_SCF[bands[i].scf_idx[ch][2]];
+                mul = mpc_CC[bands[i].res[ch] + 1] * mpc_SCF[bands[i].scf_idx[ch][2]+6];
                 for(; j < 36; j++)
                     c->sb_samples[ch][j][i] = mul * c->Q[ch][j + off];
             }

libavcodec/mpc7.c

@@ -193,7 +193,7 @@ static int get_scale_idx(GetBitContext *gb, int ref)
     int t = get_vlc2(gb, dscf_vlc.table, MPC7_DSCF_BITS, 1) - 7;
     if (t == 8)
         return get_bits(gb, 6);
-    return ref + t;
+    return av_clip_uintp2(ref + t, 7);
 }
 
 static int mpc7_decode_frame(AVCodecContext * avctx, void *data,
@@ -247,7 +247,7 @@ static int mpc7_decode_frame(AVCodecContext * avctx, void *data,
             int t = 4;
             if(i) t = get_vlc2(&gb, hdr_vlc.table, MPC7_HDR_BITS, 1) - 5;
             if(t == 4) bands[i].res[ch] = get_bits(&gb, 4);
-            else bands[i].res[ch] = bands[i-1].res[ch] + t;
+            else bands[i].res[ch] = av_clip(bands[i-1].res[ch] + t, 0, 17);
         }
 
         if(bands[i].res[0] || bands[i].res[1]){

libavcodec/mpcdata.h

@@ -22,13 +22,17 @@
 #ifndef AVCODEC_MPCDATA_H
 #define AVCODEC_MPCDATA_H
 
-static const float mpc_CC[18] = {
-    65536.0000, 21845.3333, 13107.2000, 9362.2857, 7281.7778, 4369.0667, 2114.0645,
+static const float mpc_CC[18+1] = {
+    111.285962475327f, // 32768/2/255*sqrt(3)
+    65536.0000 /* this value is never used */,
+    21845.3333, 13107.2000, 9362.2857, 7281.7778, 4369.0667, 2114.0645,
     1040.2539, 516.0315, 257.0039, 128.2505, 64.0626, 32.0156, 16.0039, 8.0010,
     4.0002, 2.0001, 1.0000
 };
 
-static const float mpc_SCF[128] = {
+static const float mpc_SCF[128+6] = {
+    920.016296386718750000, 766.355773925781250000, 638.359558105468750000,
+    531.741149902343750000, 442.930114746093750000, 368.952209472656250000,
     307.330047607421875000, 255.999984741210937500, 213.243041992187500000, 177.627334594726562500,
     147.960128784179687500, 123.247924804687500000, 102.663139343261718750, 85.516410827636718750,
     71.233520507812500000, 59.336143493652343750, 49.425861358642578125, 41.170787811279296875,