/*
 * comp_t.c
 *
 * Routine per la manipolazione dei record di accounting di Linux.
 *
 * decode_comp_t() converte le quantita` codificate in comp_t
 *	nel semplice numero che codifica.
 *
 * Martin Guy, FreakNet Medialab, Luglio 2001
 */

#include "comp_t.h"

#if 0
/* Da /usr/src/linux/kernel/acct.c */
/*
 *  encode an unsigned long into a comp_t
 *
 *  This routine has been adopted from the encode_comp_t() function in
 *  the kern_acct.c file of the FreeBSD operating system. The encoding
 *  is a 13-bit fraction with a 3-bit (base 8) exponent.
 */

#define	MANTSIZE	13			/* 13 bit mantissa. */
#define	EXPSIZE		3			/* Base 8 (3 bit) exponent. */
#define	MAXFRACT	((1 << MANTSIZE) - 1)	/* Maximum fractional value. */

static comp_t encode_comp_t(unsigned long value)
{
	int exp, rnd;

	exp = rnd = 0;
	while (value > MAXFRACT) {
		rnd = value & (1 << (EXPSIZE - 1));	/* Round up? */
		value >>= EXPSIZE;	/* Base 8 exponent == 3 bit shift. */
		exp++;
	}

	/*
         * If we need to round up, do it (and handle overflow correctly).
         */
	if (rnd && (++value > MAXFRACT)) {
		value >>= EXPSIZE;
		exp++;
	}

	/*
         * Clean it up and polish it off.
         */
	exp <<= MANTSIZE;		/* Shift the exponent into place */
	exp += value;			/* and add on the mantissa. */
	return exp;
}
#endif

/* Convertita nella funzione inversa... */
#define	MANTSIZE	13			/* 13 bit mantissa. */
#define	EXPSIZE		3			/* Base 8 (3 bit) exponent. */

unsigned long
decode_comp_t(comp_t comp)
{
	unsigned long value;
	int exp;

	exp = comp >> MANTSIZE;		/* Sappiamo che comp_t e` unsigned */
	value = comp & ((1<<MANTSIZE) - 1);

	return(value << (exp * 3));	/* Exponent is in base 8 */
}