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[bug-grep] Re: length of dec. representation of a number

From: Paul Eggert
Subject: [bug-grep] Re: length of dec. representation of a number
Date: Wed, 09 Mar 2005 15:27:04 -0800
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux)

Stepan Kasal <address@hidden> writes:

> It took me some time to decipher the macros, perhaps we could document
> them more:

OK, and to avoid further confusion I ported them to signed-magnitude
hosts (not that I ever expect to see this tested :-).

I installed the following lib/intprops.h into gnulib and coreutils,
replacing the file I had installed earlier today.

/* intprops.h -- properties of integer types

   Copyright (C) 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.

   This program 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 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by Paul Eggert.  */

#include <limits.h>

/* The extra casts in the following macros work around compiler bugs,
   e.g., in Cray C  */

/* True if the arithmetic type T is an integer type.  bool counts as
   an integer.  */
#define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)

/* True if negative values of the signed integer type T use twos
   complement, ones complement, or signed magnitude representation,
   respectively.  Much GNU code assumes twos complement, but some
   people like to be portable to all possible C hosts.  */
#define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
#define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
#define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)

/* True if the arithmetic type T is signed.  */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))

/* The maximum and minimum values for the integer type T.  These
   macros have undefined behavior if T is signed and has padding bits.
   If this is a problem for you, please let us know how to fix it for
   your host.  */
#define TYPE_MINIMUM(t) \
  ((t) (! TYPE_SIGNED (t) \
        ? (t) 0 \
        ? ~ (t) 0 \
        : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
#define TYPE_MAXIMUM(t) \
  ((t) (! TYPE_SIGNED (t) \
        ? (t) -1 \
        : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))

/* Bound on length of the string representing an integer value or type T.
   Subtract 1 for the sign bit if t is signed; log10 (2.0) < 146/485;
   add 1 for integer division truncation; add 1 more for a minus sign
   if needed.  */
#define INT_STRLEN_BOUND(t) \
  ((sizeof (t) * CHAR_BIT - 1) * 146 / 485 + 2)

/* Bound on buffer size needed to represent an integer value or type T,
   including the terminating null.  */

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