| 1 | /* floating point to accurate string |
| 2 | |
| 3 | Copyright (C) 2010-2014 Free Software Foundation, Inc. |
| 4 | |
| 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. |
| 9 | |
| 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. |
| 14 | |
| 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/>. */ |
| 17 | |
| 18 | /* Written by Paul Eggert. */ |
| 19 | |
| 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. |
| 24 | |
| 25 | This code relies on sprintf, strtod, etc. operating accurately; |
| 26 | otherwise, the resulting strings could be inaccurate or too long. */ |
| 27 | |
| 28 | #include <config.h> |
| 29 | |
| 30 | #include "ftoastr.h" |
| 31 | |
| 32 | #include <float.h> |
| 33 | #include <stdio.h> |
| 34 | #include <stdlib.h> |
| 35 | |
| 36 | #if LENGTH == 3 |
| 37 | # define FLOAT long double |
| 38 | # define FLOAT_DIG LDBL_DIG |
| 39 | # define FLOAT_MIN LDBL_MIN |
| 40 | # define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND |
| 41 | # define FTOASTR ldtoastr |
| 42 | # if HAVE_C99_STRTOLD |
| 43 | # define STRTOF strtold |
| 44 | # endif |
| 45 | #elif LENGTH == 2 |
| 46 | # define FLOAT double |
| 47 | # define FLOAT_DIG DBL_DIG |
| 48 | # define FLOAT_MIN DBL_MIN |
| 49 | # define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND |
| 50 | # define FTOASTR dtoastr |
| 51 | #else |
| 52 | # define LENGTH 1 |
| 53 | # define FLOAT float |
| 54 | # define FLOAT_DIG FLT_DIG |
| 55 | # define FLOAT_MIN FLT_MIN |
| 56 | # define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND |
| 57 | # define FTOASTR ftoastr |
| 58 | # if HAVE_STRTOF |
| 59 | # define STRTOF strtof |
| 60 | # endif |
| 61 | #endif |
| 62 | |
| 63 | /* On pre-C99 hosts, approximate strtof and strtold with strtod. This |
| 64 | may generate one or two extra digits, but that's better than not |
| 65 | working at all. */ |
| 66 | #ifndef STRTOF |
| 67 | # define STRTOF strtod |
| 68 | #endif |
| 69 | |
| 70 | /* On hosts where it's not known that snprintf works, use sprintf to |
| 71 | implement the subset needed here. Typically BUFSIZE is big enough |
| 72 | and there's little or no performance hit. */ |
| 73 | #if ! GNULIB_SNPRINTF |
| 74 | # undef snprintf |
| 75 | # define snprintf ftoastr_snprintf |
| 76 | static int |
| 77 | ftoastr_snprintf (char *buf, size_t bufsize, char const *format, |
| 78 | int width, int prec, FLOAT x) |
| 79 | { |
| 80 | char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND |
| 81 | : LENGTH == 2 ? DBL_BUFSIZE_BOUND |
| 82 | : LDBL_BUFSIZE_BOUND]; |
| 83 | int n = width; |
| 84 | if (bufsize < sizeof width_0_buffer) |
| 85 | { |
| 86 | n = sprintf (width_0_buffer, format, 0, prec, x); |
| 87 | if (n < 0) |
| 88 | return n; |
| 89 | if (n < width) |
| 90 | n = width; |
| 91 | } |
| 92 | if (n < bufsize) |
| 93 | n = sprintf (buf, format, width, prec, x); |
| 94 | return n; |
| 95 | } |
| 96 | #endif |
| 97 | |
| 98 | int |
| 99 | FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x) |
| 100 | { |
| 101 | /* The following method is simple but slow. |
| 102 | For ideas about speeding things up, please see: |
| 103 | |
| 104 | Florian Loitsch, Printing floating-point numbers quickly and accurately |
| 105 | with integers. ACM SIGPLAN notices 46, 6 (June 2010), 233-243 |
| 106 | <http://dx.doi.org/10.1145/1809028.1806623>; also see the |
| 107 | 2010-03-21 draft <http://florian.loitsch.com/tmp/article.pdf>. */ |
| 108 | |
| 109 | char format[sizeof "%-+ 0*.*Lg"]; |
| 110 | FLOAT abs_x = x < 0 ? -x : x; |
| 111 | int prec; |
| 112 | |
| 113 | char *p = format; |
| 114 | *p++ = '%'; |
| 115 | |
| 116 | /* Support flags that generate output parsable by strtof. */ |
| 117 | *p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0; |
| 118 | *p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0; |
| 119 | *p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0; |
| 120 | *p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0; |
| 121 | |
| 122 | *p++ = '*'; |
| 123 | *p++ = '.'; |
| 124 | *p++ = '*'; |
| 125 | *p = 'L'; p += 2 < LENGTH; |
| 126 | *p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g'; |
| 127 | *p = '\0'; |
| 128 | |
| 129 | for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++) |
| 130 | { |
| 131 | int n = snprintf (buf, bufsize, format, width, prec, x); |
| 132 | if (n < 0 |
| 133 | || FLOAT_PREC_BOUND <= prec |
| 134 | || (n < bufsize && STRTOF (buf, NULL) == x)) |
| 135 | return n; |
| 136 | } |
| 137 | } |