1 /* floating point to accurate string
3 Copyright (C) 2010 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert. */
28 # define FLOAT long double
29 # define FLOAT_DIG LDBL_DIG
30 # define FLOAT_MIN LDBL_MIN
31 # define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
32 # define FTOASTR ldtoastr
33 # define STRTOF strtold
36 # define FLOAT_DIG DBL_DIG
37 # define FLOAT_MIN DBL_MIN
38 # define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
39 # define FTOASTR dtoastr
40 # define STRTOF strtod
44 # define FLOAT_DIG FLT_DIG
45 # define FLOAT_MIN FLT_MIN
46 # define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
47 # define FTOASTR ftoastr
48 # define STRTOF strtof
51 /* On pre-C99 hosts, approximate strtof and strtold with strtod. This
52 may generate one or two extra digits, but that's better than not
53 working at all. Assume that strtof works if strtold does. */
54 #if LENGTH != 2 && ! HAVE_C99_STRTOLD
56 # define STRTOF strtod
60 FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
62 /* The following method is simple but slow.
63 For ideas about speeding things up, please see:
65 Florian Loitsch, Printing floating-point numbers quickly and accurately
66 with integers. ACM SIGPLAN notices 46, 6 (June 2010), 233-243
67 <http://dx.doi.org/10.1145/1809028.1806623>; also see the
68 2010-03-21 draft <http://florian.loitsch.com/tmp/article.pdf>. */
70 char format[sizeof "%-+ 0*.*Lg"];
71 FLOAT abs_x = x < 0 ? -x : x;
77 /* Support flags that generate output parsable by strtof. */
78 *p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0;
79 *p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
80 *p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
81 *p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0;
86 *p = 'L'; p += 2 < LENGTH;
87 *p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
90 for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
92 int n = snprintf (buf, bufsize, format, width, prec, x);
94 || FLOAT_PREC_BOUND <= prec
95 || (n < bufsize && STRTOF (buf, NULL) == x))