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/* -*- c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* ====================================================================
* Copyright (c) 2007 Carnegie Mellon University. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* This work was supported in part by funding from the Defense Advanced
* Research Projects Agency and the National Science Foundation of the
* United States of America, and the CMU Sphinx Speech Consortium.
*
* THIS SOFTWARE IS PROVIDED BY CARNEGIE MELLON UNIVERSITY ``AS IS'' AND
* ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY
* NOR ITS EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ====================================================================
*
*/
/**
* @file logmath.h
* @brief Fast integer logarithmic addition operations.
*
* In evaluating HMM models, probability values are often kept in log
* domain, to avoid overflow. To enable these logprob values to be
* held in int32 variables without significant loss of precision, a
* logbase of (1+epsilon) (where epsilon < 0.01 or so) is used. This
* module maintains this logbase (B).
*
* However, maintaining probabilities in log domain creates a problem
* when adding two probability values. This problem can be solved by
* table lookup. Note that:
*
* - \f$ b^z = b^x + b^y \f$
* - \f$ b^z = b^x(1 + b^{y-x}) = b^y(1 + e^{x-y}) \f$
* - \f$ z = x + log_b(1 + b^{y-x}) = y + log_b(1 + b^{x-y}) \f$
*
* So:
*
* - when \f$ y > x, z = y + logadd\_table[-(x-y)] \f$
* - when \f$ x > y, z = x + logadd\_table[-(y-x)] \f$
* - where \f$ logadd\_table[n] = log_b(1 + b^{-n}) \f$
*
* The first entry in <i>logadd_table</i> is
* simply \f$ log_b(2.0) \f$, for
* the case where \f$ y = x \f$ and thus
* \f$ z = log_b(2x) = log_b(2) + x \f$. The last entry is zero,
* where \f$ log_b(x+y) = x = y \f$ due to loss of precision.
*
* Since this table can be quite large particularly for small
* logbases, an option is provided to compress it by dropping the
* least significant bits of the table.
*/
#ifndef __LOGMATH_H__
#define __LOGMATH_H__
#include <sphinxbase/sphinxbase_export.h>
#include <sphinxbase/prim_type.h>
#include <sphinxbase/cmd_ln.h>
#ifdef __cplusplus
extern "C" {
#endif
#if 0
/* Fool Emacs. */
}
#endif
/**
* Integer log math computation table.
*
* This is exposed here to allow log-add computations to be inlined.
*/
typedef struct logadd_s logadd_t;
struct logadd_s {
/** Table, in unsigned integers of (width) bytes. */
void *table;
/** Number of elements in (table). This is never smaller than 256 (important!) */
uint32 table_size;
/** Width of elements of (table). */
uint8 width;
/** Right shift applied to elements in (table). */
int8 shift;
};
/**
* Integer log math computation class.
*/
typedef struct logmath_s logmath_t;
/**
* Obtain the log-add table from a logmath_t *
*/
#define LOGMATH_TABLE(lm) ((logadd_t *)lm)
/**
* Initialize a log math computation table.
* @param base The base B in which computation is to be done.
* @param shift Log values are shifted right by this many bits.
* @param use_table Whether to use an add table or not
* @return The newly created log math table.
*/
SPHINXBASE_EXPORT
logmath_t *logmath_init(float64 base, int shift, int use_table);
/**
* Memory-map (or read) a log table from a file.
*/
SPHINXBASE_EXPORT
logmath_t *logmath_read(const char *filename);
/**
* Write a log table to a file.
*/
SPHINXBASE_EXPORT
int32 logmath_write(logmath_t *lmath, const char *filename);
/**
* Get the log table size and dimensions.
*/
SPHINXBASE_EXPORT
int32 logmath_get_table_shape(logmath_t *lmath, uint32 *out_size,
uint32 *out_width, uint32 *out_shift);
/**
* Get the log base.
*/
SPHINXBASE_EXPORT
float64 logmath_get_base(logmath_t *lmath);
/**
* Get the smallest possible value represented in this base.
*/
SPHINXBASE_EXPORT
int logmath_get_zero(logmath_t *lmath);
/**
* Get the width of the values in a log table.
*/
SPHINXBASE_EXPORT
int logmath_get_width(logmath_t *lmath);
/**
* Get the shift of the values in a log table.
*/
SPHINXBASE_EXPORT
int logmath_get_shift(logmath_t *lmath);
/**
* Retain ownership of a log table.
*
* @return pointer to retained log table.
*/
SPHINXBASE_EXPORT
logmath_t *logmath_retain(logmath_t *lmath);
/**
* Free a log table.
*
* @return new reference count (0 if freed completely)
*/
SPHINXBASE_EXPORT
int logmath_free(logmath_t *lmath);
/**
* Add two values in log space exactly and slowly (without using add table).
*/
SPHINXBASE_EXPORT
int logmath_add_exact(logmath_t *lmath, int logb_p, int logb_q);
/**
* Add two values in log space (i.e. return log(exp(p)+exp(q)))
*/
SPHINXBASE_EXPORT
int logmath_add(logmath_t *lmath, int logb_p, int logb_q);
/**
* Convert linear floating point number to integer log in base B.
*/
SPHINXBASE_EXPORT
int logmath_log(logmath_t *lmath, float64 p);
/**
* Convert integer log in base B to linear floating point.
*/
SPHINXBASE_EXPORT
float64 logmath_exp(logmath_t *lmath, int logb_p);
/**
* Convert natural log (in floating point) to integer log in base B.
*/
SPHINXBASE_EXPORT
int logmath_ln_to_log(logmath_t *lmath, float64 log_p);
/**
* Convert integer log in base B to natural log (in floating point).
*/
SPHINXBASE_EXPORT
float64 logmath_log_to_ln(logmath_t *lmath, int logb_p);
/**
* Convert base 10 log (in floating point) to integer log in base B.
*/
SPHINXBASE_EXPORT
int logmath_log10_to_log(logmath_t *lmath, float64 log_p);
/**
* Convert integer log in base B to base 10 log (in floating point).
*/
SPHINXBASE_EXPORT
float64 logmath_log_to_log10(logmath_t *lmath, int logb_p);
#ifdef __cplusplus
}
#endif
#endif /* __LOGMATH_H__ */
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