src/libpocketsphinx/ngram_search.h File Reference

N-Gram based multi-pass search ("FBS"). More...

#include <cmd_ln.h>
#include <logmath.h>
#include <ngram_model.h>
#include <listelem_alloc.h>
#include <err.h>
#include "pocketsphinx_internal.h"
#include "hmm.h"

Go to the source code of this file.

Data Structures
struct	chan_s
	Lexical tree node data type. More...
struct	root_chan_s
	Lexical tree node data type for the first phone (root) of each dynamic HMM tree structure. More...
struct	bptbl_s
	Back pointer table (forward pass lattice; actually a tree). More...
struct	bptbl_seg_s
	Segmentation "iterator" for backpointer table results. More...
struct	lastphn_cand_s
struct	last_ltrans_t
struct	cand_sf_t
struct	bestbp_rc_s
struct	ngram_search_stats_s
	Various statistics for profiling. More...
struct	ngram_search_s
	N-Gram search module structure. More...
Defines
#define	CAND_SF_ALLOCSIZE   32
#define	NO_BP   -1
Typedefs
typedef chan_s	chan_t
	Lexical tree node data type.
typedef root_chan_s	root_chan_t
	Lexical tree node data type for the first phone (root) of each dynamic HMM tree structure.
typedef bptbl_s	bptbl_t
	Back pointer table (forward pass lattice; actually a tree).
typedef bptbl_seg_s	bptbl_seg_t
	Segmentation "iterator" for backpointer table results.
typedef lastphn_cand_s	lastphn_cand_t
typedef bestbp_rc_s	bestbp_rc_t
typedef ngram_search_stats_s	ngram_search_stats_t
	Various statistics for profiling.
typedef ngram_search_s	ngram_search_t
Functions
ps_search_t *	ngram_search_init (cmd_ln_t *config, acmod_t *acmod, s3dict_t *dict, dict2pid_t *d2p)
	Initialize the N-Gram search module.
void	ngram_search_free (ps_search_t *ngs)
	Finalize the N-Gram search module.
int	ngram_search_mark_bptable (ngram_search_t *ngs, int frame_idx)
	Record the current frame's index in the backpointer table.
void	ngram_search_save_bp (ngram_search_t *ngs, int frame_idx, int32 w, int32 score, int32 path, int32 rc)
	Enter a word in the backpointer table.
void	ngram_search_alloc_all_rc (ngram_search_t *ngs, int32 w)
	Allocate last phone channels for all possible right contexts for word w.
void	ngram_search_free_all_rc (ngram_search_t *ngs, int32 w)
	Allocate last phone channels for all possible right contexts for word w.
int	ngram_search_find_exit (ngram_search_t *ngs, int frame_idx, int32 *out_best_score)
	Find the best word exit for the current frame in the backpointer table.
char const *	ngram_search_bp_hyp (ngram_search_t *ngs, int bpidx)
	Backtrace from a given backpointer index to obtain a word hypothesis.
void	ngram_compute_seg_scores (ngram_search_t *ngs, float32 lwf)
	Compute language and acoustic scores for backpointer table entries.
ps_lattice_t *	ngram_search_lattice (ps_search_t *search)
	Construct a word lattice from the current hypothesis.
int32	ngram_search_exit_score (ngram_search_t *ngs, bptbl_t *pbe, int rcphone)
	Get the exit score for a backpointer entry with a given right context.

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Detailed Description

N-Gram based multi-pass search ("FBS").

Definition in file ngram_search.h.

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Typedef Documentation

typedef struct chan_s chan_t

Lexical tree node data type.

Not the first HMM for words, which multiplex HMMs based on different left contexts. This structure is used both in the dynamic HMM tree structure and in the per-word last-phone right context fanout.

typedef struct root_chan_s root_chan_t

Lexical tree node data type for the first phone (root) of each dynamic HMM tree structure.

Each state may have a different parent static HMM. Most fields are similar to those in chan_t.

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Function Documentation

char const* ngram_search_bp_hyp	(	ngram_search_t *	ngs,
		int	bpidx
	)

Backtrace from a given backpointer index to obtain a word hypothesis.

Returns:

a read-only string with the best hypothesis.

Definition at line 467 of file ngram_search.c.

References bptbl_s::bp, ngram_search_s::bp_table, ps_search_s::hyp_str, NO_BP, ps_search_base, ps_search_dict, and bptbl_s::wid.

int ngram_search_find_exit	(	ngram_search_t *	ngs,
		int	frame_idx,
		int32 *	out_best_score
	)

Find the best word exit for the current frame in the backpointer table.

Returns:

the backpointer index of the best word exit.

Definition at line 425 of file ngram_search.c.

References BETTER_THAN, ngram_search_s::bp_table, ngram_search_s::bp_table_idx, ngram_search_s::n_frame, NO_BP, ps_search_finish_wid, bptbl_s::score, bptbl_s::wid, and WORST_SCORE.

int ngram_search_mark_bptable	(	ngram_search_t *	ngs,
		int	frame_idx
	)

Record the current frame's index in the backpointer table.

Returns:

the current backpointer index.

Definition at line 305 of file ngram_search.c.

References ngram_search_s::bp_table_idx, ngram_search_s::bpidx, ngram_search_s::frm_wordlist, and ngram_search_s::n_frame_alloc.

Referenced by ngram_fwdflat_finish(), ngram_fwdflat_search(), ngram_fwdtree_finish(), and ngram_fwdtree_search().

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