ref: 277210ab0b851fe9d87806db2777852374e4bcac
dir: /src/stats/cst_viterbi.c/
/*************************************************************************/
/* */
/* Language Technologies Institute */
/* Carnegie Mellon University */
/* Copyright (c) 2000 */
/* All Rights Reserved. */
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/* the following conditions: */
/* 1. The code must retain the above copyright notice, this list of */
/* conditions and the following disclaimer. */
/* 2. Any modifications must be clearly marked as such. */
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/* 4. The authors' names are not used to endorse or promote products */
/* derived from this software without specific prior written */
/* permission. */
/* */
/* CARNEGIE MELLON UNIVERSITY AND THE CONTRIBUTORS TO THIS WORK */
/* DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING */
/* ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT */
/* SHALL CARNEGIE MELLON UNIVERSITY NOR THE CONTRIBUTORS BE LIABLE */
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/* */
/*************************************************************************/
/* Author: Alan W Black (awb@cs.cmu.edu) */
/* Date: August 2000 */
/*************************************************************************/
/* */
/* A Viterbi decoder */
/* */
/*************************************************************************/
#include <limits.h>
#include "cst_viterbi.h"
static void vit_point_init_path_array(cst_vit_point *n,int num_states);
static void vit_point_init_dynamic_path_array(cst_vit_point *n,
cst_vit_cand *c);
static void vit_add_paths(cst_viterbi *vd,
cst_vit_point *point,
cst_vit_path *path);
static void vit_add_path(cst_viterbi *vd,cst_vit_point *p, cst_vit_path *np);
static cst_vit_path *find_best_path(cst_viterbi *vd);
static int betterthan(cst_viterbi *v,int a, int b);
cst_vit_cand *new_vit_cand()
{
cst_vit_cand *c = cst_alloc(struct cst_vit_cand_struct,1);
return c;
}
void vit_cand_set(cst_vit_cand *vc, cst_val *val)
{
if (vc->val)
delete_val(vc->val);
vc->val = val;
val_inc_refcount(vc->val);
}
void vit_cand_set_int(cst_vit_cand *vc, int ival)
{
vc->ival = ival;
vit_cand_set(vc, int_val(ival));
}
void delete_vit_cand(cst_vit_cand *vc)
{
if (vc)
{
delete_val(vc->val);
delete_vit_cand(vc->next);
cst_free(vc);
}
}
cst_vit_path *new_vit_path()
{
cst_vit_path *p = cst_alloc(struct cst_vit_path_struct,1);
return p;
}
void delete_vit_path(cst_vit_path *vp)
{
if (vp)
{
if (vp->f)
delete_features(vp->f);
delete_vit_path(vp->next);
cst_free(vp);
}
}
cst_vit_point *new_vit_point()
{
cst_vit_point *p = cst_alloc(struct cst_vit_point_struct,1);
return p;
}
void delete_vit_point(cst_vit_point *vp)
{
int i;
if (vp)
{
if (vp->paths)
delete_vit_path(vp->paths);
if (vp->num_states != 0)
{
for (i=0; i<vp->num_states; i++)
if (vp->state_paths[i])
delete_vit_path(vp->state_paths[i]);
cst_free(vp->state_paths);
}
delete_vit_cand(vp->cands);
delete_vit_point(vp->next);
cst_free(vp);
}
}
cst_viterbi *new_viterbi(cst_vit_cand_f_t *cand_func,
cst_vit_path_f_t *path_func)
{
cst_viterbi *v = cst_alloc(struct cst_viterbi_struct,1);
v->cand_func = cand_func;
v->path_func = path_func;
v->f = new_features();
return v;
}
void delete_viterbi(cst_viterbi *vd)
{
if (vd)
{
delete_vit_point(vd->timeline);
delete_features(vd->f);
cst_free(vd);
}
return;
}
void viterbi_initialise(cst_viterbi *vd,cst_relation *r)
{
cst_item *i;
cst_vit_point *last = 0;
cst_vit_point *n = 0;
/* Construct the timeline with points for each item in relation */
/* initiallising the state tables at each point */
for (i=relation_head(r); TRUE ; i=item_next(i))
{
n = new_vit_point();
n->item = i;
if (vd->num_states > 0) /* a state based viterbi search */
vit_point_init_path_array(n,vd->num_states);
if (last)
last->next = n;
else
vd->timeline = n;
last = n;
/* we need an extra one (even if there are no items) */
/* so we go one past end of the relation */
if (i == 0)
{
vd->last_point = n;
break;
}
}
if (vd->num_states == 0) /* its a general beam search */
vd->timeline->paths = new_vit_path();
if (vd->num_states == -1) /* Dynamic number of states (# cands) */
vit_point_init_path_array(vd->timeline,1);
}
static void vit_point_init_path_array(cst_vit_point *n,int num_states)
{
n->num_states = num_states;
n->state_paths = cst_alloc(cst_vit_path*,num_states);
}
static void vit_point_init_dynamic_path_array(cst_vit_point *n,
cst_vit_cand *c)
{
int i;
cst_vit_cand *cc;
for (cc=c,i=0; cc; i++,cc=cc->next)
cc->pos = i;
vit_point_init_path_array(n,i);
}
void viterbi_decode(cst_viterbi *vd)
{
cst_vit_point *p;
cst_vit_path *np;
cst_vit_cand *c;
int i;
/* For each time point */
for (p=vd->timeline; p->next != NULL; p=p->next)
{
/* Find the candidates */
p->cands = (*vd->cand_func)(p->item,vd);
if (vd->num_states != 0) /* true viterbi */
{
if (vd->num_states == -1) /* dynamic number of states (# cands) */
vit_point_init_dynamic_path_array(p->next,p->cands);
for (i=0; i<p->num_states; i++)
{
if (((p == vd->timeline) && i==0) ||
(p->state_paths[i] != 0))
for (c=p->cands; c; c=c->next)
{
np = (*vd->path_func)(p->state_paths[i],c,vd);
vit_add_paths(vd,p->next,np);
}
}
}
else /* general beam search */
{
cst_errmsg("viterbi, general beam search not implemented\n");
/*
for (t=p->paths; t; t=t->next)
{
for (c=p->cands; c; c=c->next)
{
np = (vd->path_func)(t,c,vd);
add_path(p->next,np);
}
}
*/
}
}
}
static void vit_add_paths(cst_viterbi *vd,
cst_vit_point *point,
cst_vit_path *path)
{
/* Add a list of paths at point */
cst_vit_path *p, *next_p;
for (p=path; p; p=next_p)
{
next_p = p->next; /* as p could be deleted is not required */
vit_add_path(vd,point,p);
}
}
static void vit_add_path(cst_viterbi *vd,cst_vit_point *p, cst_vit_path *np)
{
if (p->state_paths[np->state] == 0)
{ /* we don't have one yet so this is best */
p->state_paths[np->state] = np;
}
else if (betterthan(vd,np->score,p->state_paths[np->state]->score))
{ /* its better than what we have already */
delete_vit_path(p->state_paths[np->state]);
p->state_paths[np->state] = np;
}
else
delete_vit_path(np);
}
int viterbi_result(cst_viterbi *vd,const char *n)
{
/* Find best path through the decoder, adding field to item named n */
/* with choising value */
cst_vit_path *p;
if ((vd->timeline == 0) || (vd->timeline->next == 0))
return TRUE; /* it has succeeded in the null case */
p = find_best_path(vd);
if (p == NULL) /* bummer */
return FALSE;
for (; p; p=p->from)
if (p->cand)
{
#if 1
item_set_int(p->cand->item,"cl_total_score",p->score);
item_set_int(p->cand->item,"cl_cand_score",p->cand->score);
#endif
item_set(p->cand->item,n,p->cand->val);
}
return TRUE;
}
void viterbi_copy_feature(cst_viterbi *vd,const char *featname)
{
/* copy a feature from the best path to related item */
cst_vit_path *p;
p = find_best_path(vd);
if (p == NULL) /* nothing to copy, emtpy stream or no solution */
return;
for (; p; p=p->from)
if (p->cand && feat_present(p->f, featname))
item_set(p->cand->item,featname,feat_val(p->f,featname));
return;
}
static cst_vit_path *find_best_path(cst_viterbi *vd)
{
cst_vit_point *t;
int best,worst;
cst_vit_path *best_p=NULL;
int i;
if (vd->big_is_good)
worst = -INT_MAX;
else
worst = INT_MAX;
best = worst; /* though we should be able to find something better */
t = vd->last_point;
if (vd->num_states != 0)
{
for (i=0; i<t->num_states; i++)
{
if ((t->state_paths[i] != NULL) &&
(betterthan(vd,t->state_paths[i]->score, best)))
{
best = t->state_paths[i]->score;
best_p = t->state_paths[i];
}
}
}
return best_p;
}
static int betterthan(cst_viterbi *v,int a, int b)
{
/* better may be most big or most small */
/* for probabalities big is good */
if (v->big_is_good)
return (a > b);
else
return (a < b);
}