diracdec: implement a LUT-based Golomb code parser

Still much left to optimize, but it provides a significant performance
improvement - 10% for 300Mbps (1080p30), 25% for 1.5Gbps (4k 60fps) in
comparison with the default implementation.

Signed-off-by: Rostislav Pehlivanov <rpehlivanov@obe.tv>

1 files changed, 51 insertions, 0 deletions

diff --git a/libavcodec/dirac_vlc.h b/libavcodec/dirac_vlc.h
new file mode 100644
index 0000000000..523e9ca813
--- /dev/null
+++ b/libavcodec/dirac_vlc.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2016 Open Broadcast Systems Ltd.
+ * Author        2016 Rostislav Pehlivanov <rpehlivanov@obe.tv>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_DIRAC_VLC_H
+#define AVCODEC_DIRAC_VLC_H
+
+#include <libavutil/avutil.h>
+
+/* Can be 32 bits wide for some performance gain on some machines, but it will
+ * incorrectly decode very long coefficients (usually only 1 or 2 per frame) */
+typedef uint64_t residual;
+
+#define LUT_BITS 8
+
+/* Exactly 64 bytes */
+typedef struct DiracGolombLUT {
+    residual preamble, leftover;
+    int32_t  ready[LUT_BITS];
+    int32_t  preamble_bits, leftover_bits, ready_num;
+    int8_t   need_s, sign;
+} DiracGolombLUT;
+
+av_cold int ff_dirac_golomb_reader_init(DiracGolombLUT **lut_ctx);
+
+int ff_dirac_golomb_read_32bit(DiracGolombLUT *lut_ctx, const uint8_t *buf,
+                               int bytes, uint8_t *dst, int coeffs);
+
+int ff_dirac_golomb_read_16bit(DiracGolombLUT *lut_ctx, const uint8_t *buf,
+                               int bytes, uint8_t *_dst, int coeffs);
+
+av_cold void ff_dirac_golomb_reader_end(DiracGolombLUT **lut_ctx);
+
+#endif /* AVCODEC_DIRAC_VLC_H */