comparison filter/imb.c @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

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