[FFmpeg-devel] [PATCH 3/4] avcodec/get_bits: Add get_bits_bytesize()

[Andreas Rheinhardt <ffmpegagent-at-gmail.com@ffmpeg.org>]

From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

And use it to avoid accesses to GetBitContext.buffer_end.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/bitstream.h          |  2 ++
 libavcodec/bitstream_template.h |  8 ++++++++
 libavcodec/get_bits.h           | 15 +++++++++++++++
 libavcodec/h263dec.c            |  7 ++++---
 libavcodec/h264_ps.c            |  4 ++--
 libavcodec/hevc/hevcdec.c       |  2 +-
 libavcodec/hevc/ps.c            |  6 +++---
 libavcodec/mpeg12dec.c          |  5 +++--
 8 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
index 35b7873b9c..e4d96af710 100644
--- a/libavcodec/bitstream.h
+++ b/libavcodec/bitstream.h
@@ -82,6 +82,7 @@
 # define bits_init8         bits_init8_le
 # define bits_tell          bits_tell_le
 # define bits_size          bits_size_le
+# define bits_bytesize      bits_bytesize_le
 # define bits_left          bits_left_le
 # define bits_read_bit      bits_read_bit_le
 # define bits_read_nz       bits_read_nz_le
@@ -111,6 +112,7 @@
 # define bits_init8         bits_init8_be
 # define bits_tell          bits_tell_be
 # define bits_size          bits_size_be
+# define bits_bytesize      bits_bytesize_be
 # define bits_left          bits_left_be
 # define bits_read_bit      bits_read_bit_be
 # define bits_read_nz       bits_read_nz_be
diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
index bbb8dfa555..773d40ef14 100644
--- a/libavcodec/bitstream_template.h
+++ b/libavcodec/bitstream_template.h
@@ -156,6 +156,14 @@ static inline int BS_FUNC(size)(const BSCTX *bc)
     return bc->size_in_bits;
 }
 
+/**
+ * Return buffer size in bytes.
+ */
+static inline int BS_FUNC(bytesize)(const BSCTX *bc, int round_up)
+{
+    return (bc->size_in_bits + (round_up ? 7 : 0)) >> 3;
+}
+
 /**
  * Return the number of the bits left in a buffer.
  */
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index 1954296569..c64540cf95 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -76,6 +76,7 @@
 typedef BitstreamContext GetBitContext;
 
 #define get_bits_count      bits_tell
+#define get_bits_bytesize   bits_bytesize
 #define get_bits_left       bits_left
 #define skip_bits_long      bits_skip
 #define skip_bits           bits_skip
@@ -251,6 +252,20 @@ static inline int get_bits_count(const GetBitContext *s)
     return s->index;
 }
 
+/**
+ * Get the size of the GetBitContext's buffer in bytes.
+ *
+ * @param s        the GetBitContext
+ * @param round_up If set, the number of bits will be rounded up to full bytes;
+ *                 this does not matter if the number of bits is known to be
+ *                 a multiple of eight, e.g. if the GetBitContext has been
+ *                 initialized with init_get_bits8.
+ */
+static inline int get_bits_bytesize(const GetBitContext *s, int round_up)
+{
+    return (s->size_in_bits + (round_up ? 7 : 0)) >> 3;
+}
+
 /**
  * Skips the specified number of bits.
  * @param n the number of bits to skip,
diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
index b2d0f9c409..3821472e91 100644
--- a/libavcodec/h263dec.c
+++ b/libavcodec/h263dec.c
@@ -208,7 +208,8 @@ static int decode_slice(H263DecContext *const h)
 
     if (h->c.avctx->hwaccel) {
         const uint8_t *start = h->gb.buffer + get_bits_count(&h->gb) / 8;
-        ret = FF_HW_CALL(h->c.avctx, decode_slice, start, h->gb.buffer_end - start);
+        ret = FF_HW_CALL(h->c.avctx, decode_slice, start,
+                         get_bits_bytesize(&h->gb, 0) - get_bits_count(&h->gb) / 8);
         // ensure we exit decode loop
         h->c.mb_y = h->c.mb_height;
         return ret;
@@ -372,7 +373,7 @@ static int decode_slice(H263DecContext *const h)
     if (h->c.codec_id == AV_CODEC_ID_H263          &&
         (h->c.workaround_bugs & FF_BUG_AUTODETECT) &&
         get_bits_left(&h->gb) >= 64                &&
-        AV_RB64(h->gb.buffer_end - 8) == 0xCDCDCDCDFC7F0000) {
+        AV_RB64(h->gb.buffer + (get_bits_bytesize(&h->gb, 0) - 8)) == 0xCDCDCDCDFC7F0000) {
 
         h->padding_bug_score += 32;
     }
@@ -546,7 +547,7 @@ int ff_h263_decode_frame(AVCodecContext *avctx, AVFrame *pict,
 
     if (avctx->hwaccel) {
         ret = FF_HW_CALL(avctx, start_frame, NULL,
-                         h->gb.buffer, h->gb.buffer_end - h->gb.buffer);
+                         h->gb.buffer, get_bits_bytesize(&h->gb, 0));
         if (ret < 0 )
             return ret;
     }
diff --git a/libavcodec/h264_ps.c b/libavcodec/h264_ps.c
index c698f1b80d..3a3cad7de7 100644
--- a/libavcodec/h264_ps.c
+++ b/libavcodec/h264_ps.c
@@ -294,7 +294,7 @@ int ff_h264_decode_seq_parameter_set(GetBitContext *gb, AVCodecContext *avctx,
     if (!sps)
         return AVERROR(ENOMEM);
 
-    sps->data_size = gb->buffer_end - gb->buffer;
+    sps->data_size = get_bits_bytesize(gb, 1);
     if (sps->data_size > sizeof(sps->data)) {
         av_log(avctx, AV_LOG_DEBUG, "Truncating likely oversized SPS\n");
         sps->data_size = sizeof(sps->data);
@@ -712,7 +712,7 @@ int ff_h264_decode_picture_parameter_set(GetBitContext *gb, AVCodecContext *avct
     if (!pps)
         return AVERROR(ENOMEM);
 
-    pps->data_size = gb->buffer_end - gb->buffer;
+    pps->data_size = get_bits_bytesize(gb, 1);
     if (pps->data_size > sizeof(pps->data)) {
         av_log(avctx, AV_LOG_DEBUG, "Truncating likely oversized PPS "
                "(%"SIZE_SPECIFIER" > %"SIZE_SPECIFIER")\n",
diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
index 797c9c76c9..21ecf063c5 100644
--- a/libavcodec/hevc/hevcdec.c
+++ b/libavcodec/hevc/hevcdec.c
@@ -2752,7 +2752,7 @@ static int hls_decode_entry(HEVCContext *s, GetBitContext *gb)
     const HEVCPPS   *const pps = s->pps;
     const HEVCSPS   *const sps = pps->sps;
     const uint8_t *slice_data = gb->buffer + s->sh.data_offset;
-    const size_t   slice_size = gb->buffer_end - gb->buffer - s->sh.data_offset;
+    const size_t   slice_size = get_bits_bytesize(gb, 1) - s->sh.data_offset;
     int ctb_size    = 1 << sps->log2_ctb_size;
     int more_data   = 1;
     int x_ctb       = 0;
diff --git a/libavcodec/hevc/ps.c b/libavcodec/hevc/ps.c
index 4b021ea9c1..57125d59c1 100644
--- a/libavcodec/hevc/ps.c
+++ b/libavcodec/hevc/ps.c
@@ -763,7 +763,7 @@ int ff_hevc_decode_nal_vps(GetBitContext *gb, AVCodecContext *avctx,
 {
     int i;
     int vps_id = get_bits(gb, 4);
-    ptrdiff_t nal_size = gb->buffer_end - gb->buffer;
+    ptrdiff_t nal_size = get_bits_bytesize(gb, 1);
     int ret = AVERROR_INVALIDDATA;
     uint64_t layer1_id_included = 0;
     unsigned vps_base_layer_internal_flag, vps_base_layer_available_flag;
@@ -1710,7 +1710,7 @@ int ff_hevc_decode_nal_sps(GetBitContext *gb, AVCodecContext *avctx,
 
     av_log(avctx, AV_LOG_DEBUG, "Decoding SPS\n");
 
-    sps->data_size = gb->buffer_end - gb->buffer;
+    sps->data_size = get_bits_bytesize(gb, 1);
     sps->data = av_memdup(gb->buffer, sps->data_size);
     if (!sps->data) {
         ret = AVERROR(ENOMEM);
@@ -2165,7 +2165,7 @@ int ff_hevc_decode_nal_pps(GetBitContext *gb, AVCodecContext *avctx,
     const HEVCSPS *sps = NULL;
     const HEVCVPS *vps = NULL;
     int i, ret = 0;
-    ptrdiff_t nal_size = gb->buffer_end - gb->buffer;
+    ptrdiff_t nal_size = get_bits_bytesize(gb, 1);
     unsigned int pps_id = get_ue_golomb_long(gb);
     unsigned log2_parallel_merge_level_minus2;
     HEVCPPS *pps;
diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
index 998f6aa2e5..3ea8d02e1b 100644
--- a/libavcodec/mpeg12dec.c
+++ b/libavcodec/mpeg12dec.c
@@ -1635,6 +1635,7 @@ static int slice_decode_thread(AVCodecContext *c, void *arg)
 {
     Mpeg12SliceContext *const s = *(void **) arg;
     const uint8_t *buf  = s->gb.buffer;
+    const uint8_t *end  = buf + get_bits_bytesize(&s->gb, 0);
     int mb_y            = s->c.start_mb_y;
     const int field_pic = s->c.picture_structure != PICT_FRAME;
 
@@ -1644,7 +1645,7 @@ static int slice_decode_thread(AVCodecContext *c, void *arg)
         uint32_t start_code;
         int ret;
 
-        ret = mpeg_decode_slice(s, mb_y, &buf, s->gb.buffer_end - buf);
+        ret = mpeg_decode_slice(s, mb_y, &buf, end - buf);
         emms_c();
         ff_dlog(c, "ret:%d resync:%d/%d mb:%d/%d ts:%d/%d ec:%d\n",
                 ret, s->c.resync_mb_x, s->c.resync_mb_y, s->c.mb_x, s->c.mb_y,
@@ -1666,7 +1667,7 @@ static int slice_decode_thread(AVCodecContext *c, void *arg)
             return 0;
 
         start_code = -1;
-        buf        = avpriv_find_start_code(buf, s->gb.buffer_end, &start_code);
+        buf        = avpriv_find_start_code(buf, end, &start_code);
         if (start_code < SLICE_MIN_START_CODE || start_code > SLICE_MAX_START_CODE)
             return AVERROR_INVALIDDATA;
         mb_y       = start_code - SLICE_MIN_START_CODE;
-- 
ffmpeg-codebot

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".