/*

 * floatcomp.c - Isolate floating point details.

 */

/*

 * Copyright (C) 1986, 1988, 1989, 1991-2011, 2016

 * the Free Software Foundation, Inc.

 *

 * This file is part of GAWK, the GNU implementation of the

 * AWK Programming Language.

 *

 * GAWK is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or

 * (at your option) any later version.

 *

 * GAWK is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA

 */

#include "awk.h"

#include <math.h>

#ifdef HAVE_UINTMAX_T

/* Assume IEEE-754 arithmetic on pre-C89 hosts.  */

#ifndef FLT_RADIX

#define FLT_RADIX 2

#endif

#ifndef FLT_MANT_DIG

#define FLT_MANT_DIG 24

#endif

#ifndef DBL_MANT_DIG

#define DBL_MANT_DIG 53

#endif

/*

 * The number of base-FLT_RADIX digits in an AWKNUM fraction, assuming

 * that AWKNUM is not long double.

 */

#define AWKSMALL_MANT_DIG \

  (sizeof (AWKNUM) == sizeof (double) ? DBL_MANT_DIG : FLT_MANT_DIG)

/*

 * The number of base-FLT_DIGIT digits in an AWKNUM fraction, even if

 * AWKNUM is long double.  Don't mention 'long double' unless

 * LDBL_MANT_DIG is defined, for the sake of ancient compilers that

 * lack 'long double'.

 */

#ifdef LDBL_MANT_DIG

#define AWKNUM_MANT_DIG \

  (sizeof (AWKNUM) == sizeof (long double) ? LDBL_MANT_DIG : AWKSMALL_MANT_DIG)

#else

#define AWKNUM_MANT_DIG AWKSMALL_MANT_DIG

#endif

/*

 * The number of bits in an AWKNUM fraction, assuming FLT_RADIX is

 * either 2 or 16.  IEEE and VAX formats use radix 2, and IBM

 * mainframe format uses radix 16; we know of no other radices in

 * practical use.

 */

#if FLT_RADIX != 2 && FLT_RADIX != 16

Please port the following code to your weird host;

#endif

#define AWKNUM_FRACTION_BITS (AWKNUM_MANT_DIG * (FLT_RADIX == 2 ? 1 : 4))

#define DBL_FRACTION_BITS (DBL_MANT_DIG * (FLT_RADIX == 2 ? 1 : 4))

/* Return the number of trailing zeros in N.  N must be nonzero.  */

static int

count_trailing_zeros(uintmax_t n)

{

#if 3 < (__GNUC__ + (4 <= __GNUC_MINOR__)) && UINTMAX_MAX <= ULLONG_MAX

	return __builtin_ctzll(n);

#else

	int i = 0;

	for (; (n & 3) == 0; n >>= 2)

		i += 2;

	return i + (1 & ~n);

#endif

}

/* adjust_uint --- fiddle with values, ask Paul Eggert to explain */

uintmax_t

adjust_uint(uintmax_t n)

{

	/*

	 * If uintmax_t is so wide that AWKNUM cannot represent all its

	 * values, strip leading nonzero bits of integers that are so large

	 * that they cannot be represented exactly as AWKNUMs, so that their

	 * low order bits are represented exactly, without rounding errors.

	 * This is more desirable in practice, since it means the user sees

	 * integers that are the same width as the AWKNUM fractions.

	 */

	int wordbits = CHAR_BIT * sizeof n;

	if (AWKNUM_FRACTION_BITS < wordbits) {

		uintmax_t one = 1;

		uintmax_t sentinel = one << (wordbits - AWKNUM_FRACTION_BITS);

		int shift = count_trailing_zeros(n | sentinel);

		uintmax_t mask = (one << AWKNUM_FRACTION_BITS) - 1;

		n &= mask << shift;

	}

	return n;

}

#endif /* HAVE_UINTMAX_T */