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138 lines
4.1 KiB
C
138 lines
4.1 KiB
C
/* floating point to accurate string
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Copyright (C) 2010-2013 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert. */
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/* This code can misbehave on some buggy or older platforms, when
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operating on arguments on floating types other than 'double', or
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when given unusual combinations of options. Gnulib's
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snprintf-posix module works around many of these problems.
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This code relies on sprintf, strtod, etc. operating accurately;
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otherwise, the resulting strings could be inaccurate or too long. */
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#include <config.h>
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#include "ftoastr.h"
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#include <float.h>
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#include <stdio.h>
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#include <stdlib.h>
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#if LENGTH == 3
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# define FLOAT long double
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# define FLOAT_DIG LDBL_DIG
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# define FLOAT_MIN LDBL_MIN
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# define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
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# define FTOASTR ldtoastr
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# if HAVE_C99_STRTOLD
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# define STRTOF strtold
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# endif
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#elif LENGTH == 2
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# define FLOAT double
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# define FLOAT_DIG DBL_DIG
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# define FLOAT_MIN DBL_MIN
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# define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
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# define FTOASTR dtoastr
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#else
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# define LENGTH 1
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# define FLOAT float
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# define FLOAT_DIG FLT_DIG
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# define FLOAT_MIN FLT_MIN
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# define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
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# define FTOASTR ftoastr
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# if HAVE_STRTOF
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# define STRTOF strtof
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# endif
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#endif
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/* On pre-C99 hosts, approximate strtof and strtold with strtod. This
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may generate one or two extra digits, but that's better than not
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working at all. */
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#ifndef STRTOF
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# define STRTOF strtod
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#endif
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/* On hosts where it's not known that snprintf works, use sprintf to
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implement the subset needed here. Typically BUFSIZE is big enough
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and there's little or no performance hit. */
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#if ! GNULIB_SNPRINTF
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# undef snprintf
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# define snprintf ftoastr_snprintf
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static int
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ftoastr_snprintf (char *buf, size_t bufsize, char const *format,
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int width, int prec, FLOAT x)
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{
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char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND
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: LENGTH == 2 ? DBL_BUFSIZE_BOUND
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: LDBL_BUFSIZE_BOUND];
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int n = width;
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if (bufsize < sizeof width_0_buffer)
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{
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n = sprintf (width_0_buffer, format, 0, prec, x);
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if (n < 0)
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return n;
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if (n < width)
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n = width;
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}
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if (n < bufsize)
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n = sprintf (buf, format, width, prec, x);
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return n;
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}
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#endif
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int
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FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
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{
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/* The following method is simple but slow.
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For ideas about speeding things up, please see:
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Florian Loitsch, Printing floating-point numbers quickly and accurately
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with integers. ACM SIGPLAN notices 46, 6 (June 2010), 233-243
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<http://dx.doi.org/10.1145/1809028.1806623>; also see the
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2010-03-21 draft <http://florian.loitsch.com/tmp/article.pdf>. */
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char format[sizeof "%-+ 0*.*Lg"];
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FLOAT abs_x = x < 0 ? -x : x;
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int prec;
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char *p = format;
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*p++ = '%';
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/* Support flags that generate output parsable by strtof. */
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*p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0;
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*p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
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*p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
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*p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0;
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*p++ = '*';
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*p++ = '.';
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*p++ = '*';
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*p = 'L'; p += 2 < LENGTH;
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*p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
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*p = '\0';
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for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
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{
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int n = snprintf (buf, bufsize, format, width, prec, x);
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if (n < 0
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|| FLOAT_PREC_BOUND <= prec
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|| (n < bufsize && STRTOF (buf, NULL) == x))
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return n;
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}
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}
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