[FFmpeg-devel] [PATCH 2/2] avcodec/put_bits: Make bit buffers 64-bit

[Steinar H. Gunderson]

Change BitBuf into uint64_t on all supported 64-bit platforms.
This means we need to flush the buffer less often, which is a
significant speed win. 32-bit platforms are unchanged.
Output bitstream is the same.

All API constraints are kept in place, e.g., you still cannot put_bits()
more than 31 bits at a time. This is so that codecs cannot accidentally
become 64-bit-only or similar.

Benchmarking on transcoding to various formats shows consistently
positive results:

  dnxhd                 25.60 fps ->  26.26 fps ( +2.6%)
  dvvideo               24.88 fps ->  25.17 fps ( +1.2%)
  ffv1                  14.32 fps ->  14.58 fps ( +1.8%)
  huffyuv               58.75 fps ->  63.27 fps ( +7.7%)
  jpegls                 6.22 fps ->   6.34 fps ( +1.8%)
  mjpeg                 48.65 fps ->  49.01 fps ( +0.7%)
  mpeg1video            76.41 fps ->  77.01 fps ( +0.8%)
  mpeg2video            75.99 fps ->  77.43 fps ( +1.9%)
  mpeg4                 80.66 fps ->  81.37 fps ( +0.9%)
  prores                12.35 fps ->  12.88 fps ( +4.3%)
  prores_ks             16.20 fps ->  16.80 fps ( +3.7%)
  rv20                  62.80 fps ->  62.99 fps ( +0.3%)
  utvideo               68.41 fps ->  76.32 fps (+11.6%)

Note that this includes video decoding and all other encoding work,
such as DCTs. If you isolate the actual bit-writing routines, it is
likely to be much more.

Benchmark details: Transcoding the first 30 seconds of Big Buck Bunny
in 1080p, Haswell 2.1 GHz, GCC 8.3, generally quantizer locked to
5.0. (Exceptions: DNxHD needs fixed bitrate, and JPEG-LS is so slow
that I only took the first 10 seconds, not 30.) All runs were done
ten times and single-threaded, top and bottom two results discarded to
get rid of outliers, arithmetic mean between the remaining six.
---
 libavcodec/put_bits.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libavcodec/put_bits.h b/libavcodec/put_bits.h
index c6a8f3ac14..d09c998991 100644
--- a/libavcodec/put_bits.h
+++ b/libavcodec/put_bits.h
@@ -32,9 +32,15 @@
 #include "libavutil/intreadwrite.h"
 #include "libavutil/avassert.h"
 
+#if ARCH_AARCH64 || ARCH_IA64 || ARCH_MIPS64 || ARCH_SPARC64 || ARCH_X86_64
+typedef uint64_t BitBuf;
+#define AV_WBBUF AV_WB64
+#define AV_WLBUF AV_WL64
+#else
 typedef uint32_t BitBuf;
 #define AV_WBBUF AV_WB32
 #define AV_WLBUF AV_WL32
+#endif
 
 static const int BUF_BITS = 8 * sizeof(BitBuf);
 
-- 
2.20.1