avcodec/g2meet, mjpegdec: Factor out common VLC initialization code

While just at it, remove the nb_codes parameter: It is redundant
(the number of codes is implicitly contained in the array containing how
many entries of a specific size there are) and for this reason it might
even be wrong, so it is better to check what is actually used instead.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/libavcodec/mjpegdec_common.c b/libavcodec/mjpegdec_common.c
new file mode 100644
index 0000000000..701ddfec06
--- /dev/null
+++ b/libavcodec/mjpegdec_common.c
@@ -0,0 +1,57 @@
+/*
+ * MJPEG decoder VLC code
+ * Copyright (c) 2000, 2001 Fabrice Bellard
+ * Copyright (c) 2003 Alex Beregszaszi
+ * Copyright (c) 2003-2004 Michael Niedermayer
+ *
+ * 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
+ */
+
+#include <stdint.h>
+#include "libavutil/avassert.h"
+#include "mjpegdec.h"
+#include "vlc.h"
+
+static int build_huffman_codes(uint8_t *huff_size, const uint8_t *bits_table)
+{
+    int nb_codes = 0;
+    for (int i = 1, j = 0; i <= 16; i++) {
+        nb_codes += bits_table[i];
+        av_assert1(nb_codes <= 256);
+        for (; j < nb_codes; j++)
+            huff_size[j] = i;
+    }
+    return nb_codes;
+}
+
+int ff_mjpeg_build_vlc(VLC *vlc, const uint8_t *bits_table,
+                       const uint8_t *val_table, int is_ac, void *logctx)
+{
+    uint8_t huff_size[256];
+    uint16_t huff_sym[256];
+    int nb_codes = build_huffman_codes(huff_size, bits_table);
+
+    for (int i = 0; i < nb_codes; i++) {
+        huff_sym[i] = val_table[i] + 16 * is_ac;
+
+        if (is_ac && !val_table[i])
+            huff_sym[i] = 16 * 256;
+    }
+
+    return ff_init_vlc_from_lengths(vlc, 9, nb_codes, huff_size, 1,
+                                    huff_sym, 2, 2, 0, 0, logctx);
+}