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. */
20 /* This code can misbehave on some buggy or older platforms, when
21 operating on arguments on floating types other than 'double', or
22 when given unusual combinations of options. Gnulib's
23 snprintf-posix module works around many of these problems.
25 This code relies on sprintf, strtod, etc. operating accurately;
26 otherwise, the resulting strings could be inaccurate or too long. */
36 # define FLOAT long double
37 # define FLOAT_DIG LDBL_DIG
38 # define FLOAT_MIN LDBL_MIN
39 # define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
40 # define FTOASTR ldtoastr
41 # define STRTOF strtold
44 # define FLOAT_DIG DBL_DIG
45 # define FLOAT_MIN DBL_MIN
46 # define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
47 # define FTOASTR dtoastr
48 # define STRTOF strtod
52 # define FLOAT_DIG FLT_DIG
53 # define FLOAT_MIN FLT_MIN
54 # define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
55 # define FTOASTR ftoastr
56 # define STRTOF strtof
59 /* On pre-C99 hosts, approximate strtof and strtold with strtod. This
60 may generate one or two extra digits, but that's better than not
61 working at all. Assume that strtof works if strtold does. */
62 #if LENGTH != 2 && ! HAVE_C99_STRTOLD
64 # define STRTOF strtod
67 /* On hosts where it's not known that snprintf works, use sprintf to
68 implement the subset needed here. Typically BUFSIZE is big enough
69 and there's little performance hit. */
70 #if ! GNULIB_SNPRINTF_POSIX
72 # define snprintf ftoastr_snprintf
74 ftoastr_snprintf (char *buf, size_t bufsize, char const *format,
75 int width, int prec, FLOAT x)
77 char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND
78 : LENGTH == 2 ? DBL_BUFSIZE_BOUND
79 : LDBL_BUFSIZE_BOUND];
81 if (bufsize < sizeof width_0_buffer)
83 n = sprintf (width_0_buffer, format, 0, prec, x);
90 n = sprintf (buf, format, width, prec, x);
96 FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
98 /* The following method is simple but slow.
99 For ideas about speeding things up, please see:
101 Florian Loitsch, Printing floating-point numbers quickly and accurately
102 with integers. ACM SIGPLAN notices 46, 6 (June 2010), 233-243
103 <http://dx.doi.org/10.1145/1809028.1806623>; also see the
104 2010-03-21 draft <http://florian.loitsch.com/tmp/article.pdf>. */
106 char format[sizeof "%-+ 0*.*Lg"];
107 FLOAT abs_x = x < 0 ? -x : x;
113 /* Support flags that generate output parsable by strtof. */
114 *p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0;
115 *p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
116 *p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
117 *p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0;
122 *p = 'L'; p += 2 < LENGTH;
123 *p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
126 for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
128 int n = snprintf (buf, bufsize, format, width, prec, x);
130 || FLOAT_PREC_BOUND <= prec
131 || (n < bufsize && STRTOF (buf, NULL) == x))