From: Loren Merritt Date: Mon, 29 Mar 2010 02:50:23 +0000 (+0000) Subject: optimize init_vlc(). X-Git-Tag: v0.6~410 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=3224079956811c29f6698235122b593e2d520343;p=platform%2Fupstream%2Flibav.git 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%). Originally committed as revision 22715 to svn://svn.ffmpeg.org/ffmpeg/trunk --- diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c index a04c4a0..067a58b 100644 --- a/libavcodec/bitstream.c +++ b/libavcodec/bitstream.c @@ -2,6 +2,7 @@ * Common bit i/o utils * Copyright (c) 2000, 2001 Fabrice Bellard * Copyright (c) 2002-2004 Michael Niedermayer + * Copyright (c) 2010 Loren Merritt * * alternative bitstream reader & writer by Michael Niedermayer * @@ -116,22 +117,54 @@ static int alloc_table(VLC *vlc, int size, int use_static) 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 table_nb_bits, /* first pass: map codes and compute auxillary table sizes */ for(i=0;i 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> n_prefix) + (k<> ((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_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_bits, int nb_codes, 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_bits, int nb_codes, 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; }