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[bug-gnulib] Re: [bug-grep] length of dec. representation of a number
From: |
Paul Eggert |
Subject: |
[bug-gnulib] Re: [bug-grep] length of dec. representation of a number |
Date: |
Sat, 05 Mar 2005 09:04:17 -0800 |
User-agent: |
Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux) |
address@hidden (Paul Jarc) writes:
> Just for fun, I calculated an optimal fraction. 146/485 is the
> smallest overestimate of log10(2) that can be used to calculate
> (without overflowing a 16-bit signed int) the number of bytes needed
GNU code can assume 32-bit int, so it's less obscure to use 30103 / 100000.
log10(2) is about 0.301029996, so that's pretty close.
Here's what I've drafted so far -- I haven't tested it though. I'm
planning to turn this sort of thing into a separate gnulib module with
an include file named "int-props.h" or something like that; this sort
of code is used in several places in gnulib and coreutils now, and
should be factored out.
/* The extra cast works around compiler bugs. */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* Bound on length of the string representing an integer value of type t.
Subtract one for the sign bit if t is signed;
30103 / 100000 is log10 (2) rounded up;
round the result up;
add one for a minus sign if t is signed. */
#define INT_STRLEN_BOUND(t) \
(((sizeof (t) * CHAR_BIT - TYPE_SIGNED (t)) * 30103 + 99999) / 100000 \
+ TYPE_SIGNED (t))
#define INT_BUFSIZE_BOUND(t) (INT_STRLEN_BOUND (t) + 1)
- [bug-gnulib] Re: [bug-grep] length of dec. representation of a number,
Paul Eggert <=
- [bug-gnulib] Re: length of dec. representation of a number, Stepan Kasal, 2005/03/07
- [bug-gnulib] Re: [bug-grep] length of dec. representation of a number, Jim Meyering, 2005/03/08
- [bug-gnulib] Re: [bug-grep] length of dec. representation of a number, Paul Jarc, 2005/03/09
- [bug-gnulib] Re: [bug-grep] length of dec. representation of a number, Jim Meyering, 2005/03/08
- Re: [bug-gnulib] Re: [bug-grep] length of dec. representation of a number, Stepan Kasal, 2005/03/09
- Re: [bug-gnulib] Re: [bug-grep] length of dec. representation of a number, Paul Jarc, 2005/03/09
- [bug-gnulib] Re: length of dec. representation of a number, Paul Eggert, 2005/03/09
- [bug-gnulib] Re: length of dec. representation of a number, Paul Jarc, 2005/03/10
- [bug-gnulib] Re: [bug-grep] Re: length of dec. representation of a number, Jim Meyering, 2005/03/10
- Re: length of dec. representation of a number [bug-grep] [bug-gnulib], Stepan Kasal, 2005/03/10