tomwalters@0: /*
tomwalters@0:     imb.c
tomwalters@0:     =====
tomwalters@0: 
tomwalters@0:     integer version of logarithms using units of milliBells.
tomwalters@0: 
tomwalters@0: */
tomwalters@0: 
tomwalters@0: #include <math.h>
tomwalters@0: 
tomwalters@0: #include "stitch.h"
tomwalters@0: 
tomwalters@0: #define LOG_ZERO (-10)
tomwalters@0: 
tomwalters@0: int imB( number )
tomwalters@0: long number ;
tomwalters@0: {
tomwalters@0:     register int i, out ;
tomwalters@0:     register long in ;
tomwalters@0:     static int precision = 12 ;
tomwalters@0:     static int *table = { ( int * ) 0 } ;
tomwalters@0:     static unsigned table_size ;
tomwalters@0:     static int inc ;
tomwalters@0:     double k ;
tomwalters@0: 
tomwalters@0:     if( table == ( int * ) 0 ) {
tomwalters@0: 
tomwalters@0: 	table_size = 1 << precision ;
tomwalters@0: 
tomwalters@0: 	k   = 2000. / log( 10. ) ;
tomwalters@0: 	inc = k     * log(  2. ) + 0.5 ;
tomwalters@0: 
tomwalters@0: 	table = (int *) stitch_malloc( table_size * sizeof( *table ), "imb.c for log table" ) ;
tomwalters@0: 
tomwalters@0: 	for( i=0 ; i < table_size ; i++ )
tomwalters@0: 	    table[ i ] = log( (double) ( table_size + i ) / table_size ) * k + 0.5 ;
tomwalters@0:     }
tomwalters@0: 
tomwalters@0:     if( number > 0 ) {
tomwalters@0: 
tomwalters@0: 	in = number ;
tomwalters@0: 
tomwalters@0: 	out = precision * inc ;
tomwalters@0: 
tomwalters@0: 	if( number < table_size )
tomwalters@0: 	    do {
tomwalters@0: 		in <<= 1 ;
tomwalters@0: 		out -= inc ;
tomwalters@0: 	    }
tomwalters@0: 	    while( in < table_size ) ;
tomwalters@0: 	else
tomwalters@0: 	    while( in - table_size >= table_size ) {
tomwalters@0: 		in >>= 1 ;
tomwalters@0: 		out += inc ;
tomwalters@0: 	    }
tomwalters@0: 
tomwalters@0: 	return( out + table[ in - table_size ] ) ;
tomwalters@0:     }
tomwalters@0:     else
tomwalters@0: 	return ( LOG_ZERO ) ;
tomwalters@0: }
tomwalters@0: