From c9aa80c313911b9ac44ab8099bdcc612796c6b90 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Tue, 26 Sep 2023 18:36:38 +0200
Subject: [PATCH] avcodec/mpegaudiodec_common: Avoid superfluous VLC structures

For some VLCs here, the number of bits of the VLC is
write-only, because it is hardcoded at the call site.
Therefore one can replace these VLC structures with
the only thing that is actually used: The pointer
to the VLCElem table.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mpegaudiodata.h         |  2 +-
 libavcodec/mpegaudiodec_common.c   | 16 +++++++---------
 libavcodec/mpegaudiodec_template.c |  5 +++--
 3 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/libavcodec/mpegaudiodata.h b/libavcodec/mpegaudiodata.h
index a4148a1ffe..fbad67a0b3 100644
--- a/libavcodec/mpegaudiodata.h
+++ b/libavcodec/mpegaudiodata.h
@@ -53,7 +53,7 @@ extern uint32_t ff_table_4_3_value[TABLE_4_3_SIZE];
 #endif
 
 /* VLCs for decoding layer 3 huffman tables */
-extern VLC ff_huff_vlc[16];
+extern const VLCElem *ff_huff_vlc[16];
 extern VLC ff_huff_quad_vlc[2];
 
 /* layer3 scale factor size */
diff --git a/libavcodec/mpegaudiodec_common.c b/libavcodec/mpegaudiodec_common.c
index 3a60b03e9e..6446d08967 100644
--- a/libavcodec/mpegaudiodec_common.c
+++ b/libavcodec/mpegaudiodec_common.c
@@ -64,7 +64,7 @@ const uint8_t ff_lsf_nsf_table[6][3][4] = {
 };
 
 /* mpegaudio layer 3 huffman tables */
-VLC ff_huff_vlc[16];
+const VLCElem *ff_huff_vlc[16];
 static VLCElem huff_vlc_tables[128 + 128 + 128 + 130 + 128 + 154 + 166 + 142 +
                                204 + 190 + 170 + 542 + 460 + 662 + 414];
 VLC ff_huff_quad_vlc[2];
@@ -401,6 +401,7 @@ const uint8_t ff_mpa_pretab[2][22] = {
 
 static av_cold void mpegaudiodec_common_init_static(void)
 {
+    VLCInitState state = VLC_INIT_STATE(huff_vlc_tables);
     const uint8_t *huff_sym = mpa_huffsymbols, *huff_lens = mpa_hufflens;
     int offset;
 
@@ -414,7 +415,6 @@ static av_cold void mpegaudiodec_common_init_static(void)
     }
 
     /* huffman decode tables */
-    offset = 0;
     for (int i = 0; i < 15;) {
         uint16_t tmp_symbols[256];
         int nb_codes_minus_one = mpa_huff_sizes_minus_one[i];
@@ -426,16 +426,14 @@ static av_cold void mpegaudiodec_common_init_static(void)
             tmp_symbols[j] = high << 1 | ((high && low) << 4) | low;
         }
 
-        ff_huff_vlc[++i].table         = huff_vlc_tables + offset;
-        ff_huff_vlc[i].table_allocated = FF_ARRAY_ELEMS(huff_vlc_tables) - offset;
-        ff_vlc_init_from_lengths(&ff_huff_vlc[i], 7, j,
-                                 huff_lens, 1, tmp_symbols, 2, 2,
-                                 0, VLC_INIT_STATIC_OVERLONG, NULL);
-        offset    += ff_huff_vlc[i].table_size;
+        ff_huff_vlc[++i] = ff_vlc_init_tables_from_lengths(&state, 7, j,
+                                                           huff_lens, 1,
+                                                           tmp_symbols, 2, 2,
+                                                           0, 0);
         huff_lens += j;
         huff_sym  += j;
     }
-    av_assert0(offset == FF_ARRAY_ELEMS(huff_vlc_tables));
+    av_assert1(state.size == 0);
 
     offset = 0;
     for (int i = 0; i < 2; i++) {
diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index 3e4ee79be6..c227604107 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -760,6 +760,7 @@ static int huffman_decode(MPADecodeContext *s, GranuleDef *g,
     /* low frequencies (called big values) */
     s_index = 0;
     for (i = 0; i < 3; i++) {
+        const VLCElem *vlctab;
         int j, k, l, linbits;
         j = g->region_size[i];
         if (j == 0)
@@ -768,13 +769,13 @@ static int huffman_decode(MPADecodeContext *s, GranuleDef *g,
         k       = g->table_select[i];
         l       = ff_mpa_huff_data[k][0];
         linbits = ff_mpa_huff_data[k][1];
-        vlc     = &ff_huff_vlc[l];
 
         if (!l) {
             memset(&g->sb_hybrid[s_index], 0, sizeof(*g->sb_hybrid) * 2 * j);
             s_index += 2 * j;
             continue;
         }
+        vlctab  = ff_huff_vlc[l];
 
         /* read huffcode and compute each couple */
         for (; j > 0; j--) {
@@ -787,7 +788,7 @@ static int huffman_decode(MPADecodeContext *s, GranuleDef *g,
                 if (pos >= end_pos)
                     break;
             }
-            y = get_vlc2(&s->gb, vlc->table, 7, 3);
+            y = get_vlc2(&s->gb, vlctab, 7, 3);
 
             if (!y) {
                 g->sb_hybrid[s_index    ] =