[FFmpeg-cvslog] avcodec/get_bits: add get_leb()

[James Almer]

ffmpeg | branch: master | James Almer <jamrial at gmail.com> | Sat Nov 25 11:07:16 2023 -0300| [0cc0d8c0b579f0e47052a717568dc2faa09d4e60] | committer: James Almer

avcodec/get_bits: add get_leb()

Signed-off-by: James Almer <jamrial at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=0cc0d8c0b579f0e47052a717568dc2faa09d4e60
---

 libavcodec/bitstream.h          |  2 ++
 libavcodec/bitstream_template.h | 23 +++++++++++++++++++++++
 libavcodec/get_bits.h           | 24 ++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
index 35b7873b9c..17f8a5da83 100644
--- a/libavcodec/bitstream.h
+++ b/libavcodec/bitstream.h
@@ -103,6 +103,7 @@
 # define bits_apply_sign    bits_apply_sign_le
 # define bits_read_vlc      bits_read_vlc_le
 # define bits_read_vlc_multi bits_read_vlc_multi_le
+# define bits_read_leb      bits_read_leb_le
 
 #elif defined(BITS_DEFAULT_BE)
 
@@ -132,6 +133,7 @@
 # define bits_apply_sign    bits_apply_sign_be
 # define bits_read_vlc      bits_read_vlc_be
 # define bits_read_vlc_multi bits_read_vlc_multi_be
+# define bits_read_leb      bits_read_leb_be
 
 #endif
 
diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
index 4f3d07275f..4c7101632f 100644
--- a/libavcodec/bitstream_template.h
+++ b/libavcodec/bitstream_template.h
@@ -562,6 +562,29 @@ static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t dst[8],
     return ret;
 }
 
+/**
+ * Read a unsigned integer coded as a variable number of up to eight
+ * little-endian bytes, where the MSB in a byte signals another byte
+ * must be read.
+ * Values > UINT_MAX are truncated, but all coded bits are read.
+ */
+static inline unsigned BS_FUNC(read_leb)(BSCTX *bc) {
+    int more, i = 0;
+    unsigned leb = 0;
+
+    do {
+        int byte = BS_FUNC(read)(bc, 8);
+        unsigned bits = byte & 0x7f;
+        more = byte & 0x80;
+        if (i <= 4)
+            leb |= bits << (i * 7);
+        if (++i == 8)
+            break;
+    } while (more);
+
+    return leb;
+}
+
 #undef BSCTX
 #undef BS_FUNC
 #undef BS_JOIN3
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index cfcf97c021..9e19d2a439 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -94,6 +94,7 @@ typedef BitstreamContext GetBitContext;
 #define align_get_bits      bits_align
 #define get_vlc2            bits_read_vlc
 #define get_vlc_multi       bits_read_vlc_multi
+#define get_leb             bits_read_leb
 
 #define init_get_bits8_le(s, buffer, byte_size) bits_init8_le((BitstreamContextLE*)s, buffer, byte_size)
 #define get_bits_le(s, n)                       bits_read_le((BitstreamContextLE*)s, n)
@@ -710,6 +711,29 @@ static inline int skip_1stop_8data_bits(GetBitContext *gb)
     return 0;
 }
 
+/**
+ * Read a unsigned integer coded as a variable number of up to eight
+ * little-endian bytes, where the MSB in a byte signals another byte
+ * must be read.
+ * All coded bits are read, but values > UINT_MAX are truncated.
+ */
+static inline unsigned get_leb(GetBitContext *s) {
+    int more, i = 0;
+    unsigned leb = 0;
+
+    do {
+        int byte = get_bits(s, 8);
+        unsigned bits = byte & 0x7f;
+        more = byte & 0x80;
+        if (i <= 4)
+            leb |= bits << (i * 7);
+        if (++i == 8)
+            break;
+    } while (more);
+
+    return leb;
+}
+
 #endif // CACHED_BITSTREAM_READER
 
 #endif /* AVCODEC_GET_BITS_H */