[FFmpeg-cvslog] r22715 - trunk/libavcodec/bitstream.c
lorenm
subversion
Mon Mar 29 04:50:23 CEST 2010
Author: lorenm
Date: Mon Mar 29 04:50:23 2010
New Revision: 22715
Log:
optimize init_vlc().
Reduce worst case time from O(N^2) to O(N*log(N)).
Speedup average case by a factor of 10 in ffv2 (total decoding speed +4-25%),
factor of 1.3 in ffvhuff (total +0.5%),
factor of 1.8 in indeo5 (total +1%),
factor of 1.1 in mjpeg (total +0.1%).
Modified:
trunk/libavcodec/bitstream.c
Modified: trunk/libavcodec/bitstream.c
==============================================================================
--- trunk/libavcodec/bitstream.c Mon Mar 29 03:34:33 2010 (r22714)
+++ trunk/libavcodec/bitstream.c Mon Mar 29 04:50:23 2010 (r22715)
@@ -2,6 +2,7 @@
* Common bit i/o utils
* Copyright (c) 2000, 2001 Fabrice Bellard
* Copyright (c) 2002-2004 Michael Niedermayer <michaelni at gmx.at>
+ * Copyright (c) 2010 Loren Merritt
*
* alternative bitstream reader & writer by Michael Niedermayer <michaelni at gmx.at>
*
@@ -116,22 +117,54 @@ static int alloc_table(VLC *vlc, int siz
return index;
}
-static int build_table(VLC *vlc, int table_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,
- uint32_t code_prefix, int n_prefix, int flags)
+static av_always_inline uint32_t bitswap_32(uint32_t x) {
+ return av_reverse[x&0xFF]<<24
+ | av_reverse[(x>>8)&0xFF]<<16
+ | av_reverse[(x>>16)&0xFF]<<8
+ | av_reverse[x>>24];
+}
+
+typedef struct {
+ uint8_t bits;
+ uint16_t 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 compare_vlcspec(const void *a, const void *b)
{
- int i, j, k, n, table_size, table_index, nb, n1, index, code_prefix2, symbol;
+ 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 initted
+ *
+ * @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;
uint32_t code;
VLC_TYPE (*table)[2];
table_size = 1 << table_nb_bits;
table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
#ifdef DEBUG_VLC
- av_log(NULL,AV_LOG_DEBUG,"new table index=%d size=%d code_prefix=%x n=%d\n",
- table_index, table_size, code_prefix, n_prefix);
+ av_log(NULL,AV_LOG_DEBUG,"new table index=%d size=%d\n",
+ table_index, table_size);
#endif
if (table_index < 0)
return -1;
@@ -144,33 +177,22 @@ static int build_table(VLC *vlc, int tab
/* first pass: map codes and compute auxillary table sizes */
for(i=0;i<nb_codes;i++) {
- GET_DATA(n, bits, i, bits_wrap, bits_size);
- GET_DATA(code, codes, i, codes_wrap, codes_size);
- /* we accept tables with holes */
- if (n <= 0)
- continue;
- if (!symbols)
- symbol = i;
- else
- GET_DATA(symbol, symbols, i, symbols_wrap, symbols_size);
+ n = codes[i].bits;
+ code = codes[i].code;
+ symbol = codes[i].symbol;
#if defined(DEBUG_VLC) && 0
av_log(NULL,AV_LOG_DEBUG,"i=%d n=%d code=0x%x\n", i, n, code);
#endif
- /* if code matches the prefix, it is in the table */
- n -= n_prefix;
- if (n > 0) {
- if(flags & INIT_VLC_LE)
- code_prefix2= code & (n_prefix>=32 ? 0xffffffff : (1 << n_prefix)-1);
- else
- code_prefix2= code >> n;
- if (code_prefix2 == code_prefix) {
if (n <= table_nb_bits) {
/* no need to add another table */
- j = (code << (table_nb_bits - n)) & (table_size - 1);
+ j = code >> (32 - table_nb_bits);
nb = 1 << (table_nb_bits - n);
+ inc = 1;
+ if (flags & INIT_VLC_LE) {
+ j = bitswap_32(code);
+ inc = 1 << n;
+ }
for(k=0;k<nb;k++) {
- if(flags & INIT_VLC_LE)
- j = (code >> n_prefix) + (k<<n);
#ifdef DEBUG_VLC
av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
j, i, n);
@@ -181,46 +203,41 @@ static int build_table(VLC *vlc, int tab
}
table[j][1] = n; //bits
table[j][0] = symbol;
- j++;
+ j += inc;
}
} else {
+ /* fill auxiliary table recursively */
n -= table_nb_bits;
- j = (code >> ((flags & INIT_VLC_LE) ? n_prefix : n)) & ((1 << table_nb_bits) - 1);
+ 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_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
+ table[j][1] = -subtable_bits;
#ifdef DEBUG_VLC
av_log(NULL,AV_LOG_DEBUG,"%4x: n=%d (subtable)\n",
- j, n);
+ j, codes[i].bits + table_nb_bits);
#endif
- /* compute table size */
- n1 = -table[j][1]; //bits
- if (n > n1)
- n1 = n;
- table[j][1] = -n1; //bits
+ index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
+ if (index < 0)
+ return -1;
+ /* note: realloc has been done, so reload tables */
+ table = &vlc->table[table_index];
+ table[j][0] = index; //code
+ i = k-1;
}
- }
- }
- }
-
- /* second pass : fill auxillary tables recursively */
- for(i=0;i<table_size;i++) {
- n = table[i][1]; //bits
- if (n < 0) {
- n = -n;
- if (n > table_nb_bits) {
- n = table_nb_bits;
- table[i][1] = -n; //bits
- }
- index = build_table(vlc, n, nb_codes,
- bits, bits_wrap, bits_size,
- codes, codes_wrap, codes_size,
- symbols, symbols_wrap, symbols_size,
- (flags & INIT_VLC_LE) ? (code_prefix | (i << n_prefix)) : ((code_prefix << table_nb_bits) | i),
- n_prefix + table_nb_bits, flags);
- if (index < 0)
- return -1;
- /* note: realloc has been done, so reload tables */
- table = &vlc->table[table_index];
- table[i][0] = index; //code
- }
}
return table_index;
}
@@ -258,6 +275,9 @@ int init_vlc_sparse(VLC *vlc, int nb_bit
const void *symbols, int symbols_wrap, int symbols_size,
int flags)
{
+ VLCcode buf[nb_codes];
+ int i, j;
+
vlc->bits = nb_bits;
if(flags & INIT_VLC_USE_NEW_STATIC){
if(vlc->table_size && vlc->table_size == vlc->table_allocated){
@@ -275,11 +295,31 @@ int init_vlc_sparse(VLC *vlc, int nb_bit
av_log(NULL,AV_LOG_DEBUG,"build table nb_codes=%d\n", nb_codes);
#endif
- if (build_table(vlc, nb_bits, nb_codes,
- bits, bits_wrap, bits_size,
- codes, codes_wrap, codes_size,
- symbols, symbols_wrap, symbols_size,
- 0, 0, flags) < 0) {
+ assert(symbols_size <= 2 || !symbols);
+ j = 0;
+#define COPY(condition)\
+ for (i = 0; i < nb_codes; i++) {\
+ GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
+ if (!(condition))\
+ continue;\
+ GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
+ if (flags & INIT_VLC_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(buf[j].bits > nb_bits);
+ // qsort is the slowest part of init_vlc, and could probably be improved or avoided
+ qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
+ COPY(buf[j].bits && buf[j].bits <= nb_bits);
+ nb_codes = j;
+
+ if (build_table(vlc, nb_bits, nb_codes, buf, flags) < 0) {
av_freep(&vlc->table);
return -1;
}
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