avcodec/bitstream: Move code for initializing VLCs to file of its own

bitstream.c is currently the disjoint union of three parts:
The first part is ff_log2_run, the second part are some auxiliary
functions for the PutBits-API; and the third part is the code
for creating VLCs. This commit moves the latter into a file of its own.
This has the advantage of making one of the hacks in tableprint_vlc.h
redundant as vlc.c does not include config.h (whereas the PutBits-API
part does).

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

4 files changed, 380 insertions, 352 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index dc6dc8a4bb..fb8b0e824b 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -55,6 +55,7 @@ OBJS = ac3_parser.o                                                     \
        qsv_api.o                                                        \
        raw.o                                                            \
        utils.o                                                          \
+       vlc.o                                                            \
        vorbis_parser.o                                                  \
        xiph.o                                                           \
 
diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c
index 04817f9a84..36a980646d 100644
--- a/libavcodec/bitstream.c
+++ b/libavcodec/bitstream.c
@@ -28,23 +28,13 @@
  * bitstream api.
  */
 
-#include <inttypes.h>
 #include <stdint.h>
-#include <stdlib.h>
 #include <string.h>
 
 #include "config.h"
 #include "libavutil/avassert.h"
-#include "libavutil/error.h"
-#include "libavutil/internal.h"
 #include "libavutil/intreadwrite.h"
-#include "libavutil/log.h"
-#include "libavutil/macros.h"
-#include "libavutil/mem.h"
-#include "libavutil/qsort.h"
-#include "libavutil/reverse.h"
 #include "put_bits.h"
-#include "vlc.h"
 
 const uint8_t ff_log2_run[41]={
  0, 0, 0, 0, 1, 1, 1, 1,
@@ -89,342 +79,3 @@ void ff_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
 
     put_bits(pb, bits, AV_RB16(src + 2 * words) >> (16 - bits));
 }
-
-/* VLC decoding */
-
-#define GET_DATA(v, table, i, wrap, size)                   \
-{                                                           \
-    const uint8_t *ptr = (const uint8_t *)table + i * wrap; \
-    switch(size) {                                          \
-    case 1:                                                 \
-        v = *(const uint8_t *)ptr;                          \
-        break;                                              \
-    case 2:                                                 \
-        v = *(const uint16_t *)ptr;                         \
-        break;                                              \
-    case 4:                                                 \
-    default:                                                \
-        av_assert1(size == 4);                              \
-        v = *(const uint32_t *)ptr;                         \
-        break;                                              \
-    }                                                       \
-}
-
-
-static int alloc_table(VLC *vlc, int size, int use_static)
-{
-    int index = vlc->table_size;
-
-    vlc->table_size += size;
-    if (vlc->table_size > vlc->table_allocated) {
-        if (use_static)
-            abort(); // cannot do anything, init_vlc() is used with too little memory
-        vlc->table_allocated += (1 << vlc->bits);
-        vlc->table = av_realloc_f(vlc->table, vlc->table_allocated, sizeof(VLC_TYPE) * 2);
-        if (!vlc->table) {
-            vlc->table_allocated = 0;
-            vlc->table_size = 0;
-            return AVERROR(ENOMEM);
-        }
-        memset(vlc->table + vlc->table_allocated - (1 << vlc->bits), 0, sizeof(VLC_TYPE) * 2 << vlc->bits);
-    }
-    return index;
-}
-
-#define LOCALBUF_ELEMS 1500 // the maximum currently needed is 1296 by rv34
-
-static av_always_inline uint32_t bitswap_32(uint32_t x)
-{
-    return (uint32_t)ff_reverse[ x        & 0xFF] << 24 |
-           (uint32_t)ff_reverse[(x >> 8)  & 0xFF] << 16 |
-           (uint32_t)ff_reverse[(x >> 16) & 0xFF] << 8  |
-           (uint32_t)ff_reverse[ x >> 24];
-}
-
-typedef struct VLCcode {
-    uint8_t bits;
-    VLC_TYPE symbol;
-    /** codeword, with the first bit-to-be-read in the msb
-     * (even if intended for a little-endian bitstream reader) */
-    uint32_t code;
-} VLCcode;
-
-static int vlc_common_init(VLC *vlc, int nb_bits, int nb_codes,
-                           VLCcode **buf, int flags)
-{
-    vlc->bits = nb_bits;
-    vlc->table_size = 0;
-    if (flags & INIT_VLC_USE_NEW_STATIC) {
-        av_assert0(nb_codes <= LOCALBUF_ELEMS);
-    } else {
-        vlc->table           = NULL;
-        vlc->table_allocated = 0;
-    }
-    if (nb_codes > LOCALBUF_ELEMS) {
-        *buf = av_malloc_array(nb_codes, sizeof(VLCcode));
-        if (!*buf)
-            return AVERROR(ENOMEM);
-    }
-
-    return 0;
-}
-
-static int compare_vlcspec(const void *a, const void *b)
-{
-    const VLCcode *sa = a, *sb = b;
-    return (sa->code >> 1) - (sb->code >> 1);
-}
-/**
- * Build VLC decoding tables suitable for use with get_vlc().
- *
- * @param vlc            the context to be initialized
- *
- * @param table_nb_bits  max length of vlc codes to store directly in this table
- *                       (Longer codes are delegated to subtables.)
- *
- * @param nb_codes       number of elements in codes[]
- *
- * @param codes          descriptions of the vlc codes
- *                       These must be ordered such that codes going into the same subtable are contiguous.
- *                       Sorting by VLCcode.code is sufficient, though not necessary.
- */
-static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
-                       VLCcode *codes, int flags)
-{
-    int table_size, table_index, index, code_prefix, symbol, subtable_bits;
-    int i, j, k, n, nb, inc;
-    VLC_TYPE (*table)[2];
-    uint32_t code;
-
-    if (table_nb_bits > 30)
-       return AVERROR(EINVAL);
-    table_size = 1 << table_nb_bits;
-    table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
-    ff_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
-    if (table_index < 0)
-        return table_index;
-    table = &vlc->table[table_index];
-
-    /* first pass: map codes and compute auxiliary table sizes */
-    for (i = 0; i < nb_codes; i++) {
-        n      = codes[i].bits;
-        code   = codes[i].code;
-        symbol = codes[i].symbol;
-        ff_dlog(NULL, "i=%d n=%d code=0x%"PRIx32"\n", i, n, code);
-        if (n <= table_nb_bits) {
-            /* no need to add another table */
-            j = code >> (32 - table_nb_bits);
-            nb = 1 << (table_nb_bits - n);
-            inc = 1;
-            if (flags & INIT_VLC_OUTPUT_LE) {
-                j = bitswap_32(code);
-                inc = 1 << n;
-            }
-            for (k = 0; k < nb; k++) {
-                int bits = table[j][1];
-                int oldsym  = table[j][0];
-                ff_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
-                if ((bits || oldsym) && (bits != n || oldsym != symbol)) {
-                    av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
-                    return AVERROR_INVALIDDATA;
-                }
-                table[j][1] = n; //bits
-                table[j][0] = symbol;
-                j += inc;
-            }
-        } else {
-            /* fill auxiliary table recursively */
-            n -= table_nb_bits;
-            code_prefix = code >> (32 - table_nb_bits);
-            subtable_bits = n;
-            codes[i].bits = n;
-            codes[i].code = code << table_nb_bits;
-            for (k = i+1; k < nb_codes; k++) {
-                n = codes[k].bits - table_nb_bits;
-                if (n <= 0)
-                    break;
-                code = codes[k].code;
-                if (code >> (32 - table_nb_bits) != code_prefix)
-                    break;
-                codes[k].bits = n;
-                codes[k].code = code << table_nb_bits;
-                subtable_bits = FFMAX(subtable_bits, n);
-            }
-            subtable_bits = FFMIN(subtable_bits, table_nb_bits);
-            j = (flags & INIT_VLC_OUTPUT_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
-            table[j][1] = -subtable_bits;
-            ff_dlog(NULL, "%4x: n=%d (subtable)\n",
-                    j, codes[i].bits + table_nb_bits);
-            index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
-            if (index < 0)
-                return index;
-            /* note: realloc has been done, so reload tables */
-            table = &vlc->table[table_index];
-            table[j][0] = index; //code
-            if (table[j][0] != index) {
-                avpriv_request_sample(NULL, "strange codes");
-                return AVERROR_PATCHWELCOME;
-            }
-            i = k-1;
-        }
-    }
-
-    for (i = 0; i < table_size; i++) {
-        if (table[i][1] == 0) //bits
-            table[i][0] = -1; //codes
-    }
-
-    return table_index;
-}
-
-static int vlc_common_end(VLC *vlc, int nb_bits, int nb_codes, VLCcode *codes,
-                          int flags, VLCcode localbuf[LOCALBUF_ELEMS])
-{
-    int ret = build_table(vlc, nb_bits, nb_codes, codes, flags);
-
-    if (flags & INIT_VLC_USE_NEW_STATIC) {
-        if (vlc->table_size != vlc->table_allocated &&
-            !(flags & (INIT_VLC_STATIC_OVERLONG & ~INIT_VLC_USE_NEW_STATIC)))
-            av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
-        av_assert0(ret >= 0);
-    } else {
-        if (codes != localbuf)
-            av_free(codes);
-        if (ret < 0) {
-            av_freep(&vlc->table);
-            return ret;
-        }
-    }
-    return 0;
-}
-
-/* Build VLC decoding tables suitable for use with get_vlc().
-
-   'nb_bits' sets the decoding table size (2^nb_bits) entries. The
-   bigger it is, the faster is the decoding. But it should not be too
-   big to save memory and L1 cache. '9' is a good compromise.
-
-   'nb_codes' : number of vlcs codes
-
-   'bits' : table which gives the size (in bits) of each vlc code.
-
-   'codes' : table which gives the bit pattern of of each vlc code.
-
-   'symbols' : table which gives the values to be returned from get_vlc().
-
-   'xxx_wrap' : give the number of bytes between each entry of the
-   'bits' or 'codes' tables.
-
-   'xxx_size' : gives the number of bytes of each entry of the 'bits'
-   or 'codes' tables. Currently 1,2 and 4 are supported.
-
-   'wrap' and 'size' make it possible to use any memory configuration and types
-   (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
-*/
-int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
-                       const void *bits, int bits_wrap, int bits_size,
-                       const void *codes, int codes_wrap, int codes_size,
-                       const void *symbols, int symbols_wrap, int symbols_size,
-                       int flags)
-{
-    VLCcode localbuf[LOCALBUF_ELEMS], *buf = localbuf;
-    int i, j, ret;
-
-    ret = vlc_common_init(vlc, nb_bits, nb_codes, &buf, flags);
-    if (ret < 0)
-        return ret;
-
-    av_assert0(symbols_size <= 2 || !symbols);
-    j = 0;
-#define COPY(condition)\
-    for (i = 0; i < nb_codes; i++) {                                        \
-        unsigned len;                                                       \
-        GET_DATA(len, bits, i, bits_wrap, bits_size);                       \
-        if (!(condition))                                                   \
-            continue;                                                       \
-        if (len > 3*nb_bits || len > 32) {                                  \
-            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%u) in init_vlc\n", len);\
-            if (buf != localbuf)                                            \
-                av_free(buf);                                               \
-            return AVERROR(EINVAL);                                         \
-        }                                                                   \
-        buf[j].bits = len;                                                  \
-        GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);            \
-        if (buf[j].code >= (1LL<<buf[j].bits)) {                            \
-            av_log(NULL, AV_LOG_ERROR, "Invalid code %"PRIx32" for %d in "  \
-                   "init_vlc\n", buf[j].code, i);                           \
-            if (buf != localbuf)                                            \
-                av_free(buf);                                               \
-            return AVERROR(EINVAL);                                         \
-        }                                                                   \
-        if (flags & INIT_VLC_INPUT_LE)                                      \
-            buf[j].code = bitswap_32(buf[j].code);                          \
-        else                                                                \
-            buf[j].code <<= 32 - buf[j].bits;                               \
-        if (symbols)                                                        \
-            GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size) \
-        else                                                                \
-            buf[j].symbol = i;                                              \
-        j++;                                                                \
-    }
-    COPY(len > nb_bits);
-    // qsort is the slowest part of init_vlc, and could probably be improved or avoided
-    AV_QSORT(buf, j, struct VLCcode, compare_vlcspec);
-    COPY(len && len <= nb_bits);
-    nb_codes = j;
-
-    return vlc_common_end(vlc, nb_bits, nb_codes, buf,
-                          flags, localbuf);
-}
-
-int ff_init_vlc_from_lengths(VLC *vlc, int nb_bits, int nb_codes,
-                             const int8_t *lens, int lens_wrap,
-                             const void *symbols, int symbols_wrap, int symbols_size,
-                             int offset, int flags, void *logctx)
-{
-    VLCcode localbuf[LOCALBUF_ELEMS], *buf = localbuf;
-    uint64_t code;
-    int ret, j, len_max = FFMIN(32, 3 * nb_bits);
-
-    ret = vlc_common_init(vlc, nb_bits, nb_codes, &buf, flags);
-    if (ret < 0)
-        return ret;
-
-    j = code = 0;
-    for (int i = 0; i < nb_codes; i++, lens += lens_wrap) {
-        int len = *lens;
-        if (len > 0) {
-            unsigned sym;
-
-            buf[j].bits = len;
-            if (symbols)
-                GET_DATA(sym, symbols, i, symbols_wrap, symbols_size)
-            else
-                sym = i;
-            buf[j].symbol = sym + offset;
-            buf[j++].code = code;
-        } else if (len <  0) {
-            len = -len;
-        } else
-            continue;
-        if (len > len_max || code & ((1U << (32 - len)) - 1)) {
-            av_log(logctx, AV_LOG_ERROR, "Invalid VLC (length %u)\n", len);
-            goto fail;
-        }
-        code += 1U << (32 - len);
-        if (code > UINT32_MAX + 1ULL) {
-            av_log(logctx, AV_LOG_ERROR, "Overdetermined VLC tree\n");
-            goto fail;
-        }
-    }
-    return vlc_common_end(vlc, nb_bits, j, buf, flags, localbuf);
-fail:
-    if (buf != localbuf)
-        av_free(buf);
-    return AVERROR_INVALIDDATA;
-}
-
-void ff_free_vlc(VLC *vlc)
-{
-    av_freep(&vlc->table);
-}
diff --git a/libavcodec/tableprint_vlc.h b/libavcodec/tableprint_vlc.h
index 924f97b466..d53ae5799f 100644
--- a/libavcodec/tableprint_vlc.h
+++ b/libavcodec/tableprint_vlc.h
@@ -23,7 +23,6 @@
 #ifndef AVCODEC_TABLEPRINT_VLC_H
 #define AVCODEC_TABLEPRINT_VLC_H
 
-#define FFMPEG_CONFIG_H
 #define AVUTIL_LOG_H
 #define av_log(a, ...) while(0)
 #define ff_dlog(a, ...) while(0)
@@ -37,9 +36,8 @@
 #define avpriv_request_sample(...)
 #include "tableprint.h"
 #include "vlc.h"
-#include "mathtables.c"
 #include "libavutil/reverse.c"
-#include "bitstream.c"
+#include "vlc.c"
 
 #define REPLACE_DEFINE2(type) write_##type##_array
 #define REPLACE_DEFINE(type) REPLACE_DEFINE2(type)
diff --git a/libavcodec/vlc.c b/libavcodec/vlc.c
new file mode 100644
index 0000000000..1a9bd8e6d2
--- /dev/null
+++ b/libavcodec/vlc.c
@@ -0,0 +1,378 @@
+/*
+ * API for creating VLC trees
+ * Copyright (c) 2000, 2001 Fabrice Bellard
+ * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
+ * Copyright (c) 2010 Loren Merritt
+ *
+ * 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 <inttypes.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libavutil/attributes.h"
+#include "libavutil/avassert.h"
+#include "libavutil/error.h"
+#include "libavutil/internal.h"
+#include "libavutil/log.h"
+#include "libavutil/macros.h"
+#include "libavutil/mem.h"
+#include "libavutil/qsort.h"
+#include "libavutil/reverse.h"
+#include "vlc.h"
+
+#define GET_DATA(v, table, i, wrap, size)                   \
+{                                                           \
+    const uint8_t *ptr = (const uint8_t *)table + i * wrap; \
+    switch(size) {                                          \
+    case 1:                                                 \
+        v = *(const uint8_t *)ptr;                          \
+        break;                                              \
+    case 2:                                                 \
+        v = *(const uint16_t *)ptr;                         \
+        break;                                              \
+    case 4:                                                 \
+    default:                                                \
+        av_assert1(size == 4);                              \
+        v = *(const uint32_t *)ptr;                         \
+        break;                                              \
+    }                                                       \
+}
+
+
+static int alloc_table(VLC *vlc, int size, int use_static)
+{
+    int index = vlc->table_size;
+
+    vlc->table_size += size;
+    if (vlc->table_size > vlc->table_allocated) {
+        if (use_static)
+            abort(); // cannot do anything, init_vlc() is used with too little memory
+        vlc->table_allocated += (1 << vlc->bits);
+        vlc->table = av_realloc_f(vlc->table, vlc->table_allocated, sizeof(VLC_TYPE) * 2);
+        if (!vlc->table) {
+            vlc->table_allocated = 0;
+            vlc->table_size = 0;
+            return AVERROR(ENOMEM);
+        }
+        memset(vlc->table + vlc->table_allocated - (1 << vlc->bits), 0, sizeof(VLC_TYPE) * 2 << vlc->bits);
+    }
+    return index;
+}
+
+#define LOCALBUF_ELEMS 1500 // the maximum currently needed is 1296 by rv34
+
+static av_always_inline uint32_t bitswap_32(uint32_t x)
+{
+    return (uint32_t)ff_reverse[ x        & 0xFF] << 24 |
+           (uint32_t)ff_reverse[(x >> 8)  & 0xFF] << 16 |
+           (uint32_t)ff_reverse[(x >> 16) & 0xFF] << 8  |
+           (uint32_t)ff_reverse[ x >> 24];
+}
+
+typedef struct VLCcode {
+    uint8_t bits;
+    VLC_TYPE symbol;
+    /** codeword, with the first bit-to-be-read in the msb
+     * (even if intended for a little-endian bitstream reader) */
+    uint32_t code;
+} VLCcode;
+
+static int vlc_common_init(VLC *vlc, int nb_bits, int nb_codes,
+                           VLCcode **buf, int flags)
+{
+    vlc->bits = nb_bits;
+    vlc->table_size = 0;
+    if (flags & INIT_VLC_USE_NEW_STATIC) {
+        av_assert0(nb_codes <= LOCALBUF_ELEMS);
+    } else {
+        vlc->table           = NULL;
+        vlc->table_allocated = 0;
+    }
+    if (nb_codes > LOCALBUF_ELEMS) {
+        *buf = av_malloc_array(nb_codes, sizeof(VLCcode));
+        if (!*buf)
+            return AVERROR(ENOMEM);
+    }
+
+    return 0;
+}
+
+static int compare_vlcspec(const void *a, const void *b)
+{
+    const VLCcode *sa = a, *sb = b;
+    return (sa->code >> 1) - (sb->code >> 1);
+}
+
+/**
+ * Build VLC decoding tables suitable for use with get_vlc().
+ *
+ * @param vlc            the context to be initialized
+ *
+ * @param table_nb_bits  max length of vlc codes to store directly in this table
+ *                       (Longer codes are delegated to subtables.)
+ *
+ * @param nb_codes       number of elements in codes[]
+ *
+ * @param codes          descriptions of the vlc codes
+ *                       These must be ordered such that codes going into the same subtable are contiguous.
+ *                       Sorting by VLCcode.code is sufficient, though not necessary.
+ */
+static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
+                       VLCcode *codes, int flags)
+{
+    int table_size, table_index;
+    VLC_TYPE (*table)[2];
+
+    if (table_nb_bits > 30)
+       return AVERROR(EINVAL);
+    table_size = 1 << table_nb_bits;
+    table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
+    ff_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);
+    if (table_index < 0)
+        return table_index;
+    table = &vlc->table[table_index];
+
+    /* first pass: map codes and compute auxiliary table sizes */
+    for (int i = 0; i < nb_codes; i++) {
+        int         n = codes[i].bits;
+        uint32_t code = codes[i].code;
+        int    symbol = codes[i].symbol;
+        ff_dlog(NULL, "i=%d n=%d code=0x%"PRIx32"\n", i, n, code);
+        if (n <= table_nb_bits) {
+            /* no need to add another table */
+            int   j = code >> (32 - table_nb_bits);
+            int  nb = 1 << (table_nb_bits - n);
+            int inc = 1;
+
+            if (flags & INIT_VLC_OUTPUT_LE) {
+                j = bitswap_32(code);
+                inc = 1 << n;
+            }
+            for (int k = 0; k < nb; k++) {
+                int   bits = table[j][1];
+                int oldsym = table[j][0];
+                ff_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);
+                if ((bits || oldsym) && (bits != n || oldsym != symbol)) {
+                    av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
+                    return AVERROR_INVALIDDATA;
+                }
+                table[j][1] = n; //bits
+                table[j][0] = symbol;
+                j += inc;
+            }
+        } else {
+            /* fill auxiliary table recursively */
+            uint32_t code_prefix;
+            int index, subtable_bits, j, k;
+
+            n -= table_nb_bits;
+            code_prefix = code >> (32 - table_nb_bits);
+            subtable_bits = n;
+            codes[i].bits = n;
+            codes[i].code = code << table_nb_bits;
+            for (k = i + 1; k < nb_codes; k++) {
+                n = codes[k].bits - table_nb_bits;
+                if (n <= 0)
+                    break;
+                code = codes[k].code;
+                if (code >> (32 - table_nb_bits) != code_prefix)
+                    break;
+                codes[k].bits = n;
+                codes[k].code = code << table_nb_bits;
+                subtable_bits = FFMAX(subtable_bits, n);
+            }
+            subtable_bits = FFMIN(subtable_bits, table_nb_bits);
+            j = (flags & INIT_VLC_OUTPUT_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
+            table[j][1] = -subtable_bits;
+            ff_dlog(NULL, "%4x: n=%d (subtable)\n",
+                    j, codes[i].bits + table_nb_bits);
+            index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
+            if (index < 0)
+                return index;
+            /* note: realloc has been done, so reload tables */
+            table = &vlc->table[table_index];
+            table[j][0] = index; //code
+            if (table[j][0] != index) {
+                avpriv_request_sample(NULL, "strange codes");
+                return AVERROR_PATCHWELCOME;
+            }
+            i = k-1;
+        }
+    }
+
+    for (int i = 0; i < table_size; i++) {
+        if (table[i][1] == 0) //bits
+            table[i][0] = -1; //codes
+    }
+
+    return table_index;
+}
+
+static int vlc_common_end(VLC *vlc, int nb_bits, int nb_codes, VLCcode *codes,
+                          int flags, VLCcode localbuf[LOCALBUF_ELEMS])
+{
+    int ret = build_table(vlc, nb_bits, nb_codes, codes, flags);
+
+    if (flags & INIT_VLC_USE_NEW_STATIC) {
+        if (vlc->table_size != vlc->table_allocated &&
+            !(flags & (INIT_VLC_STATIC_OVERLONG & ~INIT_VLC_USE_NEW_STATIC)))
+            av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
+        av_assert0(ret >= 0);
+    } else {
+        if (codes != localbuf)
+            av_free(codes);
+        if (ret < 0) {
+            av_freep(&vlc->table);
+            return ret;
+        }
+    }
+    return 0;
+}
+
+/* Build VLC decoding tables suitable for use with get_vlc().
+
+   'nb_bits' sets the decoding table size (2^nb_bits) entries. The
+   bigger it is, the faster is the decoding. But it should not be too
+   big to save memory and L1 cache. '9' is a good compromise.
+
+   'nb_codes' : number of vlcs codes
+
+   'bits' : table which gives the size (in bits) of each vlc code.
+
+   'codes' : table which gives the bit pattern of of each vlc code.
+
+   'symbols' : table which gives the values to be returned from get_vlc().
+
+   'xxx_wrap' : give the number of bytes between each entry of the
+   'bits' or 'codes' tables.
+
+   'xxx_size' : gives the number of bytes of each entry of the 'bits'
+   or 'codes' tables. Currently 1,2 and 4 are supported.
+
+   'wrap' and 'size' make it possible to use any memory configuration and types
+   (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
+*/
+int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
+                       const void *bits, int bits_wrap, int bits_size,
+                       const void *codes, int codes_wrap, int codes_size,
+                       const void *symbols, int symbols_wrap, int symbols_size,
+                       int flags)
+{
+    VLCcode localbuf[LOCALBUF_ELEMS], *buf = localbuf;
+    int j, ret;
+
+    ret = vlc_common_init(vlc, nb_bits, nb_codes, &buf, flags);
+    if (ret < 0)
+        return ret;
+
+    av_assert0(symbols_size <= 2 || !symbols);
+    j = 0;
+#define COPY(condition)\
+    for (int i = 0; i < nb_codes; i++) {                                    \
+        unsigned len;                                                       \
+        GET_DATA(len, bits, i, bits_wrap, bits_size);                       \
+        if (!(condition))                                                   \
+            continue;                                                       \
+        if (len > 3*nb_bits || len > 32) {                                  \
+            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%u) in init_vlc\n", len);\
+            if (buf != localbuf)                                            \
+                av_free(buf);                                               \
+            return AVERROR(EINVAL);                                         \
+        }                                                                   \
+        buf[j].bits = len;                                                  \
+        GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);            \
+        if (buf[j].code >= (1LL<<buf[j].bits)) {                            \
+            av_log(NULL, AV_LOG_ERROR, "Invalid code %"PRIx32" for %d in "  \
+                   "init_vlc\n", buf[j].code, i);                           \
+            if (buf != localbuf)                                            \
+                av_free(buf);                                               \
+            return AVERROR(EINVAL);                                         \
+        }                                                                   \
+        if (flags & INIT_VLC_INPUT_LE)                                      \
+            buf[j].code = bitswap_32(buf[j].code);                          \
+        else                                                                \
+            buf[j].code <<= 32 - buf[j].bits;                               \
+        if (symbols)                                                        \
+            GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size) \
+        else                                                                \
+            buf[j].symbol = i;                                              \
+        j++;                                                                \
+    }
+    COPY(len > nb_bits);
+    // qsort is the slowest part of init_vlc, and could probably be improved or avoided
+    AV_QSORT(buf, j, struct VLCcode, compare_vlcspec);
+    COPY(len && len <= nb_bits);
+    nb_codes = j;
+
+    return vlc_common_end(vlc, nb_bits, nb_codes, buf,
+                          flags, localbuf);
+}
+
+int ff_init_vlc_from_lengths(VLC *vlc, int nb_bits, int nb_codes,
+                             const int8_t *lens, int lens_wrap,
+                             const void *symbols, int symbols_wrap, int symbols_size,
+                             int offset, int flags, void *logctx)
+{
+    VLCcode localbuf[LOCALBUF_ELEMS], *buf = localbuf;
+    uint64_t code;
+    int ret, j, len_max = FFMIN(32, 3 * nb_bits);
+
+    ret = vlc_common_init(vlc, nb_bits, nb_codes, &buf, flags);
+    if (ret < 0)
+        return ret;
+
+    j = code = 0;
+    for (int i = 0; i < nb_codes; i++, lens += lens_wrap) {
+        int len = *lens;
+        if (len > 0) {
+            unsigned sym;
+
+            buf[j].bits = len;
+            if (symbols)
+                GET_DATA(sym, symbols, i, symbols_wrap, symbols_size)
+            else
+                sym = i;
+            buf[j].symbol = sym + offset;
+            buf[j++].code = code;
+        } else if (len <  0) {
+            len = -len;
+        } else
+            continue;
+        if (len > len_max || code & ((1U << (32 - len)) - 1)) {
+            av_log(logctx, AV_LOG_ERROR, "Invalid VLC (length %u)\n", len);
+            goto fail;
+        }
+        code += 1U << (32 - len);
+        if (code > UINT32_MAX + 1ULL) {
+            av_log(logctx, AV_LOG_ERROR, "Overdetermined VLC tree\n");
+            goto fail;
+        }
+    }
+    return vlc_common_end(vlc, nb_bits, j, buf, flags, localbuf);
+fail:
+    if (buf != localbuf)
+        av_free(buf);
+    return AVERROR_INVALIDDATA;
+}
+
+void ff_free_vlc(VLC *vlc)
+{
+    av_freep(&vlc->table);
+}