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437 lines
13 KiB
C
437 lines
13 KiB
C
/*
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* Copyright (C) 2007 Vitor Sessak <vitor1001@gmail.com>
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*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* Codebook Generator using the ELBG algorithm
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*/
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#include <string.h>
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#include "libavutil/lfg.h"
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#include "elbg.h"
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#include "avcodec.h"
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#define DELTA_ERR_MAX 0.1 ///< Precision of the ELBG algorithm (as percentual error)
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/**
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* In the ELBG jargon, a cell is the set of points that are closest to a
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* codebook entry. Not to be confused with a RoQ Video cell. */
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typedef struct cell_s {
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int index;
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struct cell_s *next;
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} cell;
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/**
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* ELBG internal data
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*/
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typedef struct{
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int error;
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int dim;
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int numCB;
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int *codebook;
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cell **cells;
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int *utility;
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int *utility_inc;
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int *nearest_cb;
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int *points;
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AVLFG *rand_state;
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int *scratchbuf;
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} elbg_data;
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static inline int distance_limited(int *a, int *b, int dim, int limit)
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{
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int i, dist=0;
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for (i=0; i<dim; i++) {
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dist += (a[i] - b[i])*(a[i] - b[i]);
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if (dist > limit)
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return INT_MAX;
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}
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return dist;
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}
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static inline void vect_division(int *res, int *vect, int div, int dim)
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{
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int i;
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if (div > 1)
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for (i=0; i<dim; i++)
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res[i] = ROUNDED_DIV(vect[i],div);
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else if (res != vect)
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memcpy(res, vect, dim*sizeof(int));
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}
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static int eval_error_cell(elbg_data *elbg, int *centroid, cell *cells)
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{
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int error=0;
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for (; cells; cells=cells->next)
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error += distance_limited(centroid, elbg->points + cells->index*elbg->dim, elbg->dim, INT_MAX);
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return error;
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}
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static int get_closest_codebook(elbg_data *elbg, int index)
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{
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int i, pick=0, diff, diff_min = INT_MAX;
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for (i=0; i<elbg->numCB; i++)
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if (i != index) {
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diff = distance_limited(elbg->codebook + i*elbg->dim, elbg->codebook + index*elbg->dim, elbg->dim, diff_min);
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if (diff < diff_min) {
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pick = i;
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diff_min = diff;
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}
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}
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return pick;
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}
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static int get_high_utility_cell(elbg_data *elbg)
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{
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int i=0;
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/* Using linear search, do binary if it ever turns to be speed critical */
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int r = av_lfg_get(elbg->rand_state)%elbg->utility_inc[elbg->numCB-1] + 1;
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while (elbg->utility_inc[i] < r)
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i++;
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assert(!elbg->cells[i]);
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return i;
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}
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/**
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* Implementation of the simple LBG algorithm for just two codebooks
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*/
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static int simple_lbg(elbg_data *elbg,
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int dim,
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int *centroid[3],
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int newutility[3],
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int *points,
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cell *cells)
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{
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int i, idx;
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int numpoints[2] = {0,0};
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int *newcentroid[2] = {
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elbg->scratchbuf + 3*dim,
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elbg->scratchbuf + 4*dim
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};
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cell *tempcell;
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memset(newcentroid[0], 0, 2 * dim * sizeof(*newcentroid[0]));
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newutility[0] =
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newutility[1] = 0;
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for (tempcell = cells; tempcell; tempcell=tempcell->next) {
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idx = distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX)>=
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distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX);
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numpoints[idx]++;
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for (i=0; i<dim; i++)
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newcentroid[idx][i] += points[tempcell->index*dim + i];
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}
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vect_division(centroid[0], newcentroid[0], numpoints[0], dim);
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vect_division(centroid[1], newcentroid[1], numpoints[1], dim);
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for (tempcell = cells; tempcell; tempcell=tempcell->next) {
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int dist[2] = {distance_limited(centroid[0], points + tempcell->index*dim, dim, INT_MAX),
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distance_limited(centroid[1], points + tempcell->index*dim, dim, INT_MAX)};
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int idx = dist[0] > dist[1];
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newutility[idx] += dist[idx];
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}
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return newutility[0] + newutility[1];
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}
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static void get_new_centroids(elbg_data *elbg, int huc, int *newcentroid_i,
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int *newcentroid_p)
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{
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cell *tempcell;
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int *min = newcentroid_i;
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int *max = newcentroid_p;
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int i;
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for (i=0; i< elbg->dim; i++) {
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min[i]=INT_MAX;
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max[i]=0;
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}
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for (tempcell = elbg->cells[huc]; tempcell; tempcell = tempcell->next)
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for(i=0; i<elbg->dim; i++) {
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min[i]=FFMIN(min[i], elbg->points[tempcell->index*elbg->dim + i]);
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max[i]=FFMAX(max[i], elbg->points[tempcell->index*elbg->dim + i]);
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}
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for (i=0; i<elbg->dim; i++) {
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int ni = min[i] + (max[i] - min[i])/3;
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int np = min[i] + (2*(max[i] - min[i]))/3;
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newcentroid_i[i] = ni;
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newcentroid_p[i] = np;
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}
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}
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/**
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* Add the points in the low utility cell to its closest cell. Split the high
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* utility cell, putting the separed points in the (now empty) low utility
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* cell.
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*
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* @param elbg Internal elbg data
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* @param indexes {luc, huc, cluc}
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* @param newcentroid A vector with the position of the new centroids
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*/
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static void shift_codebook(elbg_data *elbg, int *indexes,
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int *newcentroid[3])
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{
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cell *tempdata;
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cell **pp = &elbg->cells[indexes[2]];
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while(*pp)
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pp= &(*pp)->next;
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*pp = elbg->cells[indexes[0]];
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elbg->cells[indexes[0]] = NULL;
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tempdata = elbg->cells[indexes[1]];
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elbg->cells[indexes[1]] = NULL;
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while(tempdata) {
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cell *tempcell2 = tempdata->next;
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int idx = distance_limited(elbg->points + tempdata->index*elbg->dim,
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newcentroid[0], elbg->dim, INT_MAX) >
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distance_limited(elbg->points + tempdata->index*elbg->dim,
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newcentroid[1], elbg->dim, INT_MAX);
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tempdata->next = elbg->cells[indexes[idx]];
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elbg->cells[indexes[idx]] = tempdata;
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tempdata = tempcell2;
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}
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}
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static void evaluate_utility_inc(elbg_data *elbg)
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{
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int i, inc=0;
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for (i=0; i < elbg->numCB; i++) {
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if (elbg->numCB*elbg->utility[i] > elbg->error)
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inc += elbg->utility[i];
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elbg->utility_inc[i] = inc;
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}
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}
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static void update_utility_and_n_cb(elbg_data *elbg, int idx, int newutility)
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{
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cell *tempcell;
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elbg->utility[idx] = newutility;
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for (tempcell=elbg->cells[idx]; tempcell; tempcell=tempcell->next)
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elbg->nearest_cb[tempcell->index] = idx;
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}
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/**
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* Evaluate if a shift lower the error. If it does, call shift_codebooks
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* and update elbg->error, elbg->utility and elbg->nearest_cb.
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*
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* @param elbg Internal elbg data
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* @param idx {luc (low utility cell, huc (high utility cell), cluc (closest cell to low utility cell)}
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*/
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static void try_shift_candidate(elbg_data *elbg, int idx[3])
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{
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int j, k, olderror=0, newerror, cont=0;
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int newutility[3];
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int *newcentroid[3] = {
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elbg->scratchbuf,
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elbg->scratchbuf + elbg->dim,
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elbg->scratchbuf + 2*elbg->dim
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};
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cell *tempcell;
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for (j=0; j<3; j++)
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olderror += elbg->utility[idx[j]];
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memset(newcentroid[2], 0, elbg->dim*sizeof(int));
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for (k=0; k<2; k++)
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for (tempcell=elbg->cells[idx[2*k]]; tempcell; tempcell=tempcell->next) {
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cont++;
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for (j=0; j<elbg->dim; j++)
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newcentroid[2][j] += elbg->points[tempcell->index*elbg->dim + j];
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}
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vect_division(newcentroid[2], newcentroid[2], cont, elbg->dim);
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get_new_centroids(elbg, idx[1], newcentroid[0], newcentroid[1]);
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newutility[2] = eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[0]]);
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newutility[2] += eval_error_cell(elbg, newcentroid[2], elbg->cells[idx[2]]);
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newerror = newutility[2];
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newerror += simple_lbg(elbg, elbg->dim, newcentroid, newutility, elbg->points,
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elbg->cells[idx[1]]);
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if (olderror > newerror) {
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shift_codebook(elbg, idx, newcentroid);
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elbg->error += newerror - olderror;
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for (j=0; j<3; j++)
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update_utility_and_n_cb(elbg, idx[j], newutility[j]);
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evaluate_utility_inc(elbg);
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}
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}
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/**
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* Implementation of the ELBG block
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*/
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static void do_shiftings(elbg_data *elbg)
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{
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int idx[3];
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evaluate_utility_inc(elbg);
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for (idx[0]=0; idx[0] < elbg->numCB; idx[0]++)
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if (elbg->numCB*elbg->utility[idx[0]] < elbg->error) {
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if (elbg->utility_inc[elbg->numCB-1] == 0)
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return;
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idx[1] = get_high_utility_cell(elbg);
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idx[2] = get_closest_codebook(elbg, idx[0]);
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if (idx[1] != idx[0] && idx[1] != idx[2])
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try_shift_candidate(elbg, idx);
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}
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}
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#define BIG_PRIME 433494437LL
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void ff_init_elbg(int *points, int dim, int numpoints, int *codebook,
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int numCB, int max_steps, int *closest_cb,
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AVLFG *rand_state)
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{
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int i, k;
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if (numpoints > 24*numCB) {
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/* ELBG is very costly for a big number of points. So if we have a lot
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of them, get a good initial codebook to save on iterations */
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int *temp_points = av_malloc(dim*(numpoints/8)*sizeof(int));
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for (i=0; i<numpoints/8; i++) {
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k = (i*BIG_PRIME) % numpoints;
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memcpy(temp_points + i*dim, points + k*dim, dim*sizeof(int));
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}
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ff_init_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
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ff_do_elbg(temp_points, dim, numpoints/8, codebook, numCB, 2*max_steps, closest_cb, rand_state);
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av_free(temp_points);
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} else // If not, initialize the codebook with random positions
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for (i=0; i < numCB; i++)
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memcpy(codebook + i*dim, points + ((i*BIG_PRIME)%numpoints)*dim,
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dim*sizeof(int));
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}
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void ff_do_elbg(int *points, int dim, int numpoints, int *codebook,
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int numCB, int max_steps, int *closest_cb,
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AVLFG *rand_state)
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{
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int dist;
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elbg_data elbg_d;
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elbg_data *elbg = &elbg_d;
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int i, j, k, last_error, steps=0;
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int *dist_cb = av_malloc(numpoints*sizeof(int));
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int *size_part = av_malloc(numCB*sizeof(int));
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cell *list_buffer = av_malloc(numpoints*sizeof(cell));
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cell *free_cells;
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int best_dist, best_idx = 0;
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elbg->error = INT_MAX;
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elbg->dim = dim;
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elbg->numCB = numCB;
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elbg->codebook = codebook;
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elbg->cells = av_malloc(numCB*sizeof(cell *));
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elbg->utility = av_malloc(numCB*sizeof(int));
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elbg->nearest_cb = closest_cb;
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elbg->points = points;
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elbg->utility_inc = av_malloc(numCB*sizeof(int));
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elbg->scratchbuf = av_malloc(5*dim*sizeof(int));
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elbg->rand_state = rand_state;
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do {
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free_cells = list_buffer;
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last_error = elbg->error;
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steps++;
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memset(elbg->utility, 0, numCB*sizeof(int));
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memset(elbg->cells, 0, numCB*sizeof(cell *));
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elbg->error = 0;
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/* This loop evaluate the actual Voronoi partition. It is the most
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costly part of the algorithm. */
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for (i=0; i < numpoints; i++) {
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best_dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + best_idx*elbg->dim, dim, INT_MAX);
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for (k=0; k < elbg->numCB; k++) {
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dist = distance_limited(elbg->points + i*elbg->dim, elbg->codebook + k*elbg->dim, dim, best_dist);
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if (dist < best_dist) {
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best_dist = dist;
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best_idx = k;
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}
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}
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elbg->nearest_cb[i] = best_idx;
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dist_cb[i] = best_dist;
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elbg->error += dist_cb[i];
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elbg->utility[elbg->nearest_cb[i]] += dist_cb[i];
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free_cells->index = i;
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free_cells->next = elbg->cells[elbg->nearest_cb[i]];
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elbg->cells[elbg->nearest_cb[i]] = free_cells;
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free_cells++;
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}
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do_shiftings(elbg);
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memset(size_part, 0, numCB*sizeof(int));
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memset(elbg->codebook, 0, elbg->numCB*dim*sizeof(int));
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for (i=0; i < numpoints; i++) {
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size_part[elbg->nearest_cb[i]]++;
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for (j=0; j < elbg->dim; j++)
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elbg->codebook[elbg->nearest_cb[i]*elbg->dim + j] +=
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elbg->points[i*elbg->dim + j];
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}
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for (i=0; i < elbg->numCB; i++)
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vect_division(elbg->codebook + i*elbg->dim,
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elbg->codebook + i*elbg->dim, size_part[i], elbg->dim);
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} while(((last_error - elbg->error) > DELTA_ERR_MAX*elbg->error) &&
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(steps < max_steps));
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av_free(dist_cb);
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av_free(size_part);
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av_free(elbg->utility);
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av_free(list_buffer);
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av_free(elbg->cells);
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av_free(elbg->utility_inc);
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av_free(elbg->scratchbuf);
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}
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