libsent/src/phmm/addlog.c

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/*
 * Copyright (c) 1991-2011 Kawahara Lab., Kyoto University
 * Copyright (c) 2000-2005 Shikano Lab., Nara Institute of Science and Technology
 * Copyright (c) 2005-2011 Julius project team, Nagoya Institute of Technology
 * All rights reserved
 */

#include <sent/stddefs.h>
#include <sent/hmm.h>

#define TBLSIZE 500000          ///< Table size (precision depends on this)
#define VRANGE 15               ///< Must be larger than -LOG_ADDMIN
#define TMAG 33333.3333         ///< TBLSIZE / VRANGE

static LOGPROB tbl[TBLSIZE];    
static boolean built_tbl = FALSE;

void
make_log_tbl()
{
  LOGPROB f;
  int i;

  if (built_tbl == FALSE) {
    jlog("Stat: addlog: generating addlog table (size = %d kB)\n", (TBLSIZE * sizeof(LOGPROB)) / 1024);
    for (i=0;i<TBLSIZE;i++){
      f = - ((float)VRANGE * (float)i / (float)TBLSIZE);
      tbl[i] = log(1 + exp(f));
      /*if (i < 10 || i > TBLSIZE - 10) j_printf("%f: %d(%f)\n", f, i, tbl[i]);*/
    }
    jlog("Stat: addlog: addlog table generated\n");
    built_tbl = TRUE;
  }
}

LOGPROB
addlog(LOGPROB x, LOGPROB y)
{
  /* return(log(exp(x)+exp(y))) */
  LOGPROB tmp;
  unsigned int idx;
  
  if (x < y) {
    if ((tmp = x - y) < LOG_ADDMIN) return y;
    else {
      idx = (unsigned int)((- tmp) * TMAG + 0.5);
      /* jlog("%f == %f\n",tbl[idx],log(1 + exp(tmp))); */
      return (y + tbl[idx]);
    }
  } else {
    if ((tmp = y - x) < LOG_ADDMIN) return x;
    else {
      idx =(unsigned int)((- tmp) * TMAG + 0.5);
      /* jlog("%f == %f\n",tbl[idx],log(1 + exp(tmp))); */
      return (x + tbl[idx]);
    }
  }
}

LOGPROB
addlog_array(LOGPROB *a, int n)
{
  LOGPROB tmp;
  LOGPROB x,y;
  unsigned int idx;

  y = LOG_ZERO;
  for(n--; n >= 0; n--) {
    x = a[n];
    if (x > y) {
      tmp = x; x = y; y = tmp;
    }
    /* always y >= x */
    if ((tmp = x - y) < LOG_ADDMIN) continue;
    else {
      idx = (unsigned int)((- tmp) * TMAG + 0.5);
      y += tbl[idx];
    }
  }
  return(y);
}