julius/search_bestfirst_v1.c File Reference

Viterbi path update and hypothesis score calculation on the 2nd pass, using backscan algorithm. More...

#include <julius.h>

Include dependency graph for search_bestfirst_v1.c:

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Functions

void free_node_exec (NODE *node)

void free_node (NODE *node)

void clear_stocker ()

NODE * cpy_node (NODE *dst, NODE *src)

NODE * newnode ()

void malloc_wordtrellis ()

void free_wordtrellis ()

void scan_word (NODE *now, HTK_Param *param)

void next_word (NODE *now, NODE *new, NEXTWORD *nword, HTK_Param *param, BACKTRELLIS *backtrellis)

void start_word (NODE *new, NEXTWORD *nword, HTK_Param *param, BACKTRELLIS *backtrellis)

void last_next_word (NODE *now, NODE *new, HTK_Param *param)

Variables

static NODE * stocker_root = NULL

< Define if want triphone debug messages Node stocker for recycle

static LOGPROB * wordtrellis [2]

Buffer to compute viterbi path of a word.

static int tn

Temporal pointer to current buffer.

static int tl

Temporal pointer to previous buffer.

static LOGPROB * g

Buffer to hold source viterbi scores.

static HMM_Logical ** phmmseq

Phoneme sequence to be computed.

static int phmmlen_max

Maximum length of phmmseq.

Detailed Description

Viterbi path update and hypothesis score calculation on the 2nd pass, using backscan algorithm.

Author:: Akinobu Lee

Date:: Sun Sep 11 23:54:53 2005

This file has functions for score calculations on the 2nd pass. It includes Viterbi path update calculation of a hypothesis, calculations of scores and word trellis connection at word expansion.

The cross-word triphone will be computed not at word expansion time, but at later pop up for rapid decoding. This is called "backscan" altgorithm. These functions are enabled when PASS2_STRICT_IWCD is UNDEFINED in config.h. If defined, "nextscan" functions in search_bestfirst_v2.c are used instead.

Here we use "delayed cross-word context handling" method for connection of next word and last word of the hypothesis for speeding up decoding:

Only right context of the tail phone in the next word is considered when generating a new hypothesis (next_word()).

The whole context dependency will be fully computed when the hypothesis is once pushed to stack and later popped in scan_word().

This method avoid computing full context-dependency handling for all generated hypothesis in next_word(), and only re-compute it after primising ones are popped from stack later. This speeds up decoding. But since the context dependency is not considered in the total hypothesis score (computed in next_word()).

The actual implimentation:

In nextword(), the tail phone in the new word is modified considering the right context (= head phone in the last word of source hypothesis), and the outprob on the connection point between backtrellis and forward trellis is computed using the triphone.

In scan_word(), not only the new word but also the head phone in the previous word should be modified and re-scanned. To realize this '1-phoneme backscan' procedure, hypothesis nodes have to keep forward scores not only at the last HMM state (g[] in NODE), but also at the backscan restart point (= before the head phone in the previous word, g_prev[] in NODE).

Note that the actual implementation becomes a little more complicated to handle 1-phoneme words...

Revision: 1.5

Definition in file search_bestfirst_v1.c.

Function Documentation

void free_node_exec ( NODE * node )

Free a hypothesis node actually.

Parameters:

node

[in] hypothesis node

Definition at line 140 of file search_bestfirst_v1.c.

Referenced by clear_stocker().

void free_node ( NODE * node )

Stock an unused hypothesis node for recycle.

Parameters:

node

[in] hypothesis node

Definition at line 169 of file search_bestfirst_v1.c.

Referenced by free_all_nodes(), put_all_in_stack(), put_to_stack(), result_reorder_and_output(), and wchmm_fbs().

void clear_stocker ( )

Clear the node stocker for recycle.

Definition at line 199 of file search_bestfirst_v1.c.

NODE* cpy_node	(	NODE *	dst,
		NODE *	src
	)

Copy the content of node to another.

Parameters:

	dst	[out] target hypothesis
	src	[in] source hypothesis

Returns:: the value of dst.

Definition at line 238 of file search_bestfirst_v1.c.

Referenced by last_next_word().

NODE* newnode ( )

Allocate a new hypothesis node. If the node stocker is not empty, the one in the stocker is re-used. Otherwise, allocate as new.

Returns:: pointer to the newly allocated node.

Definition at line 314 of file search_bestfirst_v1.c.

Referenced by wchmm_fbs().

void malloc_wordtrellis ( )

Allocate work area for trellis computation of a word.

Definition at line 418 of file search_bestfirst_v1.c.

Referenced by wchmm_fbs().

void free_wordtrellis ( )

Free the work area for trellis computation of a word.

Definition at line 456 of file search_bestfirst_v1.c.

void scan_word	(	NODE *	now,
		HTK_Param *	param
	)

Compute the forward viterbi for the last word to update forward scores and ready for word connection.

Parameters:

	now	[i/o] hypothesis
	param	[in] input parameter vectors

Definition at line 555 of file search_bestfirst_v1.c.

void next_word	(	NODE *	now,
		NODE *	new,
		NEXTWORD *	nword,
		HTK_Param *	param,
		BACKTRELLIS *	backtrellis
	)

Connect a new word to generate a next hypothesis. The optimal connection point and new sentence score of the new hypothesis will be estimated by looking up the corresponding words on word trellis.

Parameters:

	now	[in] source hypothesis
	new	[out] pointer to save the newly generated hypothesis
	nword	[in] next word to be connected
	param	[in] input parameter vector
	backtrellis	[in] word trellis

Definition at line 1353 of file search_bestfirst_v1.c.

void start_word	(	NODE *	new,
		NEXTWORD *	nword,
		HTK_Param *	param,
		BACKTRELLIS *	backtrellis
	)

Generate an initial hypothesis from given word.

Parameters:

	new	[out] pointer to save the newly generated hypothesis
	nword	[in] words of the first candidates
	param	[in] input parameter vector
	backtrellis	[in] word trellis

Definition at line 1587 of file search_bestfirst_v1.c.

Referenced by wchmm_fbs().

void last_next_word	(	NODE *	now,
		NODE *	new,
		HTK_Param *	param
	)

Hypothesis termination: set the final sentence scores of hypothesis that has already reached to the end.

Parameters:

	now	[in] hypothesis that has already reached to the end
	new	[out] pointer to save the final sentence information
	param	[in] input parameter vectors

Definition at line 1674 of file search_bestfirst_v1.c.

Generated on Tue Dec 26 16:16:57 2006 for Julius by

1.5.0


Functions
void	free_node_exec (NODE *node)
void	free_node (NODE *node)
void	clear_stocker ()
NODE *	cpy_node (NODE dst, NODE src)
NODE *	newnode ()
void	malloc_wordtrellis ()
void	free_wordtrellis ()
void	scan_word (NODE now, HTK_Param param)
void	next_word (NODE now, NODE new, NEXTWORD nword, HTK_Param param, BACKTRELLIS *backtrellis)
void	start_word (NODE new, NEXTWORD nword, HTK_Param param, BACKTRELLIS backtrellis)
void	last_next_word (NODE now, NODE new, HTK_Param *param)
Variables
static NODE *	stocker_root = NULL
	< Define if want triphone debug messages Node stocker for recycle
static LOGPROB *	wordtrellis [2]
	Buffer to compute viterbi path of a word.
static int	tn
	Temporal pointer to current buffer.
static int	tl
	Temporal pointer to previous buffer.
static LOGPROB *	g
	Buffer to hold source viterbi scores.
static HMM_Logical **	phmmseq
	Phoneme sequence to be computed.
static int	phmmlen_max
	Maximum length of phmmseq.