timespec_get: New module.
[gnulib.git] / lib / ftoastr.c
blob0ee0407ec2727f6be91c1dd35b64387238699eb0
1 /* floating point to accurate string
3 Copyright (C) 2010-2021 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 <https://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. */
28 #include <config.h>
30 #include "ftoastr.h"
32 #include <float.h>
33 #include <stdio.h>
34 #include <stdlib.h>
36 #ifdef C_LOCALE
37 # include "c-snprintf.h"
38 # include "c-strtod.h"
39 # define PREFIX(name) c_ ## name
40 #else
41 # define PREFIX(name) name
42 #endif
44 #if LENGTH == 3
45 # define FLOAT long double
46 # define FLOAT_DIG LDBL_DIG
47 # define FLOAT_MIN LDBL_MIN
48 # define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
49 # define FTOASTR PREFIX (ldtoastr)
50 # define PROMOTED_FLOAT long double
51 # define STRTOF PREFIX (strtold)
52 #elif LENGTH == 2
53 # define FLOAT double
54 # define FLOAT_DIG DBL_DIG
55 # define FLOAT_MIN DBL_MIN
56 # define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
57 # define FTOASTR PREFIX (dtoastr)
58 # define PROMOTED_FLOAT double
59 #else
60 # define LENGTH 1
61 # define FLOAT float
62 # define FLOAT_DIG FLT_DIG
63 # define FLOAT_MIN FLT_MIN
64 # define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
65 # define FTOASTR PREFIX (ftoastr)
66 # define PROMOTED_FLOAT double
67 # if HAVE_STRTOF
68 # define STRTOF strtof
69 # endif
70 #endif
72 /* On pre-C99 hosts, approximate strtof with strtod. This
73 may generate one or two extra digits, but that's better than not
74 working at all. */
75 #ifndef STRTOF
76 # define STRTOF PREFIX (strtod)
77 #endif
79 /* On hosts where it's not known that snprintf works, use sprintf to
80 implement the subset needed here. Typically BUFSIZE is big enough
81 and there's little or no performance hit. */
82 #ifdef C_LOCALE
83 # undef snprintf
84 # define snprintf c_snprintf
85 #elif ! GNULIB_SNPRINTF
86 # undef snprintf
87 # define snprintf ftoastr_snprintf
88 static int
89 ftoastr_snprintf (char *buf, size_t bufsize, char const *format,
90 int width, int prec, FLOAT x)
92 PROMOTED_FLOAT promoted_x = x;
93 char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND
94 : LENGTH == 2 ? DBL_BUFSIZE_BOUND
95 : LDBL_BUFSIZE_BOUND];
96 int n = width;
97 if (bufsize < sizeof width_0_buffer)
99 n = sprintf (width_0_buffer, format, 0, prec, promoted_x);
100 if (n < 0)
101 return n;
102 if (n < width)
103 n = width;
105 if (n < bufsize)
106 n = sprintf (buf, format, width, prec, promoted_x);
107 return n;
109 #endif
112 FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
114 /* The following method is simple but slow.
115 For ideas about speeding things up, please see:
117 Andrysco M, Jhala R, Lerner S. Printing floating-point numbers:
118 a faster, always correct method. ACM SIGPLAN notices - POPL '16.
119 2016;51(1):555-67 <https://doi.org/10.1145/2914770.2837654>; draft at
120 <https://cseweb.ucsd.edu/~lerner/papers/fp-printing-popl16.pdf>. */
122 PROMOTED_FLOAT promoted_x = x;
123 char format[sizeof "%-+ 0*.*Lg"];
124 FLOAT abs_x = x < 0 ? -x : x;
125 int prec;
127 char *p = format;
128 *p++ = '%';
130 /* Support flags that generate output parsable by strtof. */
131 *p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0;
132 *p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
133 *p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
134 *p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0;
136 *p++ = '*';
137 *p++ = '.';
138 *p++ = '*';
139 *p = 'L'; p += 2 < LENGTH;
140 *p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
141 *p = '\0';
143 for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
145 int n = snprintf (buf, bufsize, format, width, prec, promoted_x);
146 if (n < 0
147 || FLOAT_PREC_BOUND <= prec
148 || (n < bufsize && STRTOF (buf, NULL) == x))
149 return n;