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