[FFmpeg-cvslog] truehd_core: Use byte offsets instead of bit offsets

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at gmail.com> | Sat Jul  6 16:18:03 2019 +0200| [836065b27a0f5b8268c2fb6c6e825ac3b63168f0] | committer: Paul B Mahol

truehd_core: Use byte offsets instead of bit offsets

Words of 16 bit are the unit for TrueHD's size and offset fields;
in particular the sizes of the high-level structures of TrueHD are
always a multiple of a byte; yet truehd_core unnecessarily used
bit offsets at several places. This has been changed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=836065b27a0f5b8268c2fb6c6e825ac3b63168f0
---

 libavcodec/truehd_core_bsf.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/libavcodec/truehd_core_bsf.c b/libavcodec/truehd_core_bsf.c
index 47684235db..8ea80d3015 100644
--- a/libavcodec/truehd_core_bsf.c
+++ b/libavcodec/truehd_core_bsf.c
@@ -45,7 +45,7 @@ static int truehd_core_filter(AVBSFContext *ctx, AVPacket *out)
     int ret, i, last_offset = 0;
     int in_size, out_size;
     int have_header = 0;
-    int substream_bits = 0;
+    int substream_bytes = 0;
     int end;
 
     ret = ff_bsf_get_packet(ctx, &in);
@@ -85,30 +85,32 @@ static int truehd_core_filter(AVBSFContext *ctx, AVPacket *out)
         units[i].offset = get_bits(&gbc, 12);
         if (i < 3) {
             last_offset = units[i].offset * 2;
-            substream_bits += 16;
+            substream_bytes += 2;
         }
 
         if (units[i].bits[0]) {
             units[i].optional = get_bits(&gbc, 16);
             if (i < 3)
-                substream_bits += 16;
+                substream_bytes += 2;
         }
     }
-    end = get_bits_count(&gbc);
+    end = get_bits_count(&gbc) >> 3;
 
-    out_size = ((end + 7) >> 3) + 4 + last_offset;
+    out_size = end + 4 + last_offset;
     if (out_size < in_size) {
-        int bpos = 0, reduce = (end - have_header * 28 * 8 - substream_bits) >> 4;
+        int bpos = 0, reduce = end - have_header * 28 - substream_bytes;
         uint16_t parity_nibble, dts = AV_RB16(in->data + 2);
         uint16_t auheader;
 
+        av_assert1(reduce % 2 == 0);
+
         ret = av_new_packet(out, out_size);
         if (ret < 0)
             goto fail;
 
         AV_WB16(out->data + 2, dts);
         parity_nibble = dts;
-        out->size -= reduce * 2;
+        out->size     -= reduce;
         parity_nibble ^= out->size / 2;
 
         if (have_header) {
@@ -146,8 +148,8 @@ static int truehd_core_filter(AVBSFContext *ctx, AVPacket *out)
         parity_nibble &= 0xF;
 
         memcpy(out->data + have_header * 28 + 4 + bpos,
-               in->data + 4 + (end >> 3),
-               out_size - (4 + (end >> 3)));
+               in->data + 4 + end,
+               out_size - (4 + end));
         auheader  = (parity_nibble ^ 0xF) << 12;
         auheader |= (out->size / 2) & 0x0fff;
         AV_WB16(out->data, auheader);