[FFmpeg-devel] [PATCH 1/2] Expose and start using skip_remaining

[Christophe Gisquet]

Bitstream readers sometimes have already checked there are enough
bits, and the check is redundant.
---
 libavcodec/bitstream.h          |  8 +++++---
 libavcodec/bitstream_template.h | 22 +++++++++++-----------
 libavcodec/get_bits.h           |  1 +
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
index 35b7873b9c..dd043fb349 100644
--- a/libavcodec/bitstream.h
+++ b/libavcodec/bitstream.h
@@ -95,6 +95,7 @@
 # define bits_peek_signed   bits_peek_signed_le
 # define bits_peek_signed_nz bits_peek_signed_nz_le
 # define bits_skip          bits_skip_le
+# define bits_skip_remaining bits_skip_remaining_le
 # define bits_seek          bits_seek_le
 # define bits_align         bits_align_le
 # define bits_read_xbits    bits_read_xbits_le
@@ -124,6 +125,7 @@
 # define bits_peek_signed   bits_peek_signed_be
 # define bits_peek_signed_nz bits_peek_signed_nz_be
 # define bits_skip          bits_skip_be
+# define bits_skip_remaining bits_skip_remaining_be
 # define bits_seek          bits_seek_be
 # define bits_align         bits_align_be
 # define bits_read_xbits    bits_read_xbits_be
@@ -146,7 +148,7 @@
         n     = table[index].len;                           \
                                                             \
         if (max_depth > 1 && n < 0) {                       \
-            bits_skip(bc, bits);                            \
+            skip_remaining(bc, bits);                       \
                                                             \
             nb_bits = -n;                                   \
                                                             \
@@ -154,7 +156,7 @@
             level = table[index].level;                     \
             n     = table[index].len;                       \
             if (max_depth > 2 && n < 0) {                   \
-                bits_skip(bc, nb_bits);                     \
+                skip_remaining(bc, nb_bits);                \
                 nb_bits = -n;                               \
                                                             \
                 index = bits_peek(bc, nb_bits) + level;     \
@@ -163,7 +165,7 @@
             }                                               \
         }                                                   \
         run = table[index].run;                             \
-        bits_skip(bc, n);                                   \
+        skip_remaining(bc, n);                              \
     } while (0)
 
 #endif /* AVCODEC_BITSTREAM_H */
diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
index 0308e3a924..3f90fc6a07 100644
--- a/libavcodec/bitstream_template.h
+++ b/libavcodec/bitstream_template.h
@@ -175,7 +175,7 @@ static inline uint64_t BS_FUNC(priv_val_show)(BSCTX *bc, unsigned int n)
 #endif
 }
 
-static inline void BS_FUNC(priv_skip_remaining)(BSCTX *bc, unsigned int n)
+static inline void BS_FUNC(skip_remaining)(BSCTX *bc, unsigned int n)
 {
 #ifdef BITSTREAM_TEMPLATE_LE
     bc->bits >>= n;
@@ -192,7 +192,7 @@ static inline uint64_t BS_FUNC(priv_val_get)(BSCTX *bc, unsigned int n)
     av_assert2(n > 0 && n < 64);
 
     ret = BS_FUNC(priv_val_show)(bc, n);
-    BS_FUNC(priv_skip_remaining)(bc, n);
+    BS_FUNC(skip_remaining)(bc, n);
 
     return ret;
 }
@@ -375,7 +375,7 @@ static inline int BS_FUNC(peek_signed)(BSCTX *bc, unsigned int n)
 static inline void BS_FUNC(skip)(BSCTX *bc, unsigned int n)
 {
     if (n < bc->bits_valid)
-        BS_FUNC(priv_skip_remaining)(bc, n);
+        BS_FUNC(skip_remaining)(bc, n);
     else {
         n -= bc->bits_valid;
         bc->bits       = 0;
@@ -389,7 +389,7 @@ static inline void BS_FUNC(skip)(BSCTX *bc, unsigned int n)
         }
         BS_FUNC(priv_refill_64)(bc);
         if (n)
-            BS_FUNC(priv_skip_remaining)(bc, n);
+            BS_FUNC(skip_remaining)(bc, n);
     }
 }
 
@@ -425,7 +425,7 @@ static inline int BS_FUNC(read_xbits)(BSCTX *bc, unsigned int n)
 {
     int32_t cache = BS_FUNC(peek)(bc, 32);
     int sign = ~cache >> 31;
-    BS_FUNC(priv_skip_remaining)(bc, n);
+    BS_FUNC(skip_remaining)(bc, n);
 
     return ((((uint32_t)(sign ^ cache)) >> (32 - n)) ^ sign) - sign;
 }
@@ -508,14 +508,14 @@ static inline int BS_FUNC(read_vlc)(BSCTX *bc, const VLCElem *table,
     int n        = table[idx].len;
 
     if (max_depth > 1 && n < 0) {
-        BS_FUNC(priv_skip_remaining)(bc, bits);
+        BS_FUNC(skip_remaining)(bc, bits);
         code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
         if (max_depth > 2 && n < 0) {
-            BS_FUNC(priv_skip_remaining)(bc, nb_bits);
+            BS_FUNC(skip_remaining)(bc, nb_bits);
             code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
         }
     }
-    BS_FUNC(priv_skip_remaining)(bc, n);
+    BS_FUNC(skip_remaining)(bc, n);
 
     return code;
 }
@@ -534,17 +534,17 @@ static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t *dst,
         code = table[idx].sym;
         n = table[idx].len;
         if (max_depth > 1 && n < 0) {
-            BS_FUNC(priv_skip_remaining)(bc, bits);
+            BS_FUNC(skip_remaining)(bc, bits);
             code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
             if (max_depth > 2 && n < 0) {
-                BS_FUNC(priv_skip_remaining)(bc, nb_bits);
+                BS_FUNC(skip_remaining)(bc, nb_bits);
                 code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
             }
         }
         AV_WN16(dst, code);
         ret = n > 0;
     }
-    BS_FUNC(priv_skip_remaining)(bc, n);
+    BS_FUNC(skip_remaining)(bc, n);
 
     return ret;
 }
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index 0594e104bb..2e24632cb5 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -79,6 +79,7 @@ typedef BitstreamContext GetBitContext;
 #define get_bits_left       bits_left
 #define skip_bits_long      bits_skip
 #define skip_bits           bits_skip
+#define skip_remaining      bits_skip_remaining
 #define get_bits            bits_read_nz
 #define get_bitsz           bits_read
 #define get_bits_long       bits_read
-- 
2.42.0