Improve decoding quality for lossy wavpack.

This reverts e6e7bfc1 and 365e1ec2.
The code may be incorrect both before and after the revert, but we
do not have any samples that were fixed by the original commits.

Fixes ticket #871.

libavcodec/wavpack.c

@@ -112,8 +112,7 @@ typedef struct WavpackFrameContext {
     int extra_bits;
     int and, or, shift;
     int post_shift;
-    int hybrid, hybrid_bitrate;
-    int hybrid_maxclip, hybrid_minclip;
+    int hybrid, hybrid_bitrate, hybrid_maxclip;
     int float_flag;
     int float_shift;
     int float_max_exp;
@@ -413,10 +412,10 @@ static inline int wv_get_value_integer(WavpackFrameContext *s, uint32_t *crc,
     }
 
     bit = (S & s->and) | s->or;
-    bit = ((S + bit) << s->shift) - bit;
+    bit = (((S + bit) << s->shift) - bit);
 
     if (s->hybrid)
-        bit = av_clip(bit, s->hybrid_minclip, s->hybrid_maxclip);
+        bit = av_clip(bit, -s->hybrid_maxclip - 1, s->hybrid_maxclip);
 
     return bit << s->post_shift;
 }
@@ -764,7 +763,7 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
     const uint8_t *orig_buf = buf;
     const uint8_t *buf_end  = buf + buf_size;
     int i, j, id, size, ssize, weights, t;
-    int bpp, chan, chmask, orig_bpp;
+    int bpp, chan, chmask;
 
     if (buf_size == 0) {
         *got_frame_ptr = 0;
@@ -800,16 +799,15 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
     s->frame_flags = AV_RL32(buf); buf += 4;
     bpp = av_get_bytes_per_sample(avctx->sample_fmt);
     samples = (uint8_t*)samples + bpp * wc->ch_offset;
-    orig_bpp = ((s->frame_flags & 0x03) + 1) << 3;
 
     s->stereo         = !(s->frame_flags & WV_MONO);
     s->stereo_in      =  (s->frame_flags & WV_FALSE_STEREO) ? 0 : s->stereo;
     s->joint          =   s->frame_flags & WV_JOINT_STEREO;
     s->hybrid         =   s->frame_flags & WV_HYBRID_MODE;
     s->hybrid_bitrate =   s->frame_flags & WV_HYBRID_BITRATE;
-    s->post_shift     = bpp * 8 - orig_bpp + ((s->frame_flags >> 13) & 0x1f);
-    s->hybrid_maxclip = (( 1LL << (orig_bpp - 1)) - 1) >> s->post_shift;
-    s->hybrid_minclip = ((-1LL << (orig_bpp - 1)))     >> s->post_shift;
+    s->hybrid_maxclip = (1LL << ((((s->frame_flags & 0x03) + 1) << 3) - 1)) - 1;
+    s->post_shift     = 8 * (bpp - 1 - (s->frame_flags & 0x03)) +
+                        ((s->frame_flags >> 13) & 0x1f);
     s->CRC            = AV_RL32(buf); buf += 4;
     if (wc->mkv_mode)
         buf += 4; //skip block size;
@@ -970,15 +968,6 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
                 s->and   = 1;
                 s->shift = buf[3];
             }
-            /* original WavPack decoder forces 32-bit lossy sound to be treated
-             * as 24-bit one in order to have proper clipping
-             */
-            if (s->hybrid && bpp == 4 && s->post_shift < 8 && s->shift > 8) {
-                s->post_shift += 8;
-                s->shift      -= 8;
-                s->hybrid_maxclip >>= 8;
-                s->hybrid_minclip >>= 8;
-            }
             buf += 4;
             break;
         case WP_ID_FLOATINFO: