Lagarith decoder by Nathan Caldwell, saintdev at gmail

Originally committed as revision 26270 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 58 insertions, 0 deletions

diff --git a/libavcodec/lagarithrac.c b/libavcodec/lagarithrac.c
new file mode 100644
index 0000000000..0cbc3b84df
--- /dev/null
+++ b/libavcodec/lagarithrac.c
@@ -0,0 +1,58 @@
+/*
+ * Lagarith range decoder
+ * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
+ * Copyright (c) 2009 David Conrad
+ *
+ * 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
+ */
+
+/**
+ * @file libavcodec/lagarithrac.c
+ * Lagarith range decoder
+ * @author Nathan Caldwell
+ * @author David Conrad
+ */
+
+#include "get_bits.h"
+#include "lagarithrac.h"
+
+void lag_rac_init(lag_rac *l, GetBitContext *gb, int length)
+{
+    int i, j;
+
+    /* According to reference decoder "1st byte is garbage",
+     * however, it gets skipped by the call to align_get_bits()
+     */
+    align_get_bits(gb);
+    l->bytestream_start =
+    l->bytestream       = gb->buffer + get_bits_count(gb) / 8;
+    l->bytestream_end   = l->bytestream_start + length;
+
+    l->range        = 0x80;
+    l->low          = *l->bytestream >> 1;
+    l->hash_shift   = FFMAX(l->scale - 8, 0);
+
+    for (i = j = 0; i < 256; i++) {
+        unsigned r = i << l->hash_shift;
+        while (l->prob[j + 1] <= r)
+            j++;
+        l->range_hash[i] = j;
+    }
+
+    /* Add conversion factor to hash_shift so we don't have to in lag_get_rac. */
+    l->hash_shift += 23;
+}