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/* floating point to accurate string
Copyright (C) 2010-2023 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
/* This code can misbehave on some buggy or older platforms, when
operating on arguments on floating types other than 'double', or
when given unusual combinations of options. Gnulib's
snprintf-posix module works around many of these problems.
This code relies on sprintf, strtod, etc. operating accurately;
otherwise, the resulting strings could be inaccurate or too long. */
#include <config.h>
#include "ftoastr.h"
#include <float.h>
#include <stdio.h>
#include <stdlib.h>
#ifdef C_LOCALE
# include "c-snprintf.h"
# include "c-strtod.h"
# define PREFIX(name) c_ ## name
#else
# define PREFIX(name) name
#endif
#if LENGTH == 3
# define FLOAT long double
# define FLOAT_DIG LDBL_DIG
# define FLOAT_MIN LDBL_MIN
# define FLOAT_PREC_BOUND _GL_LDBL_PREC_BOUND
# define FTOASTR PREFIX (ldtoastr)
# define PROMOTED_FLOAT long double
# define STRTOF PREFIX (strtold)
#elif LENGTH == 2
# define FLOAT double
# define FLOAT_DIG DBL_DIG
# define FLOAT_MIN DBL_MIN
# define FLOAT_PREC_BOUND _GL_DBL_PREC_BOUND
# define FTOASTR PREFIX (dtoastr)
# define PROMOTED_FLOAT double
#else
# define LENGTH 1
# define FLOAT float
# define FLOAT_DIG FLT_DIG
# define FLOAT_MIN FLT_MIN
# define FLOAT_PREC_BOUND _GL_FLT_PREC_BOUND
# define FTOASTR PREFIX (ftoastr)
# define PROMOTED_FLOAT double
# if HAVE_STRTOF
# define STRTOF strtof
# endif
#endif
/* On pre-C99 hosts, approximate strtof with strtod. This
may generate one or two extra digits, but that's better than not
working at all. */
#ifndef STRTOF
# define STRTOF PREFIX (strtod)
#endif
/* On hosts where it's not known that snprintf works, use sprintf to
implement the subset needed here. Typically BUFSIZE is big enough
and there's little or no performance hit. */
#ifdef C_LOCALE
# undef snprintf
# define snprintf c_snprintf
#elif ! GNULIB_SNPRINTF
# undef snprintf
# define snprintf ftoastr_snprintf
static int
ftoastr_snprintf (char *buf, size_t bufsize, char const *format,
int width, int prec, FLOAT x)
{
PROMOTED_FLOAT promoted_x = x;
char width_0_buffer[LENGTH == 1 ? FLT_BUFSIZE_BOUND
: LENGTH == 2 ? DBL_BUFSIZE_BOUND
: LDBL_BUFSIZE_BOUND];
int n = width;
if (bufsize < sizeof width_0_buffer)
{
n = sprintf (width_0_buffer, format, 0, prec, promoted_x);
if (n < 0)
return n;
if (n < width)
n = width;
}
if (n < bufsize)
n = sprintf (buf, format, width, prec, promoted_x);
return n;
}
#endif
int
FTOASTR (char *buf, size_t bufsize, int flags, int width, FLOAT x)
{
/* The following method is simple but slow.
For ideas about speeding things up, please see:
Andrysco M, Jhala R, Lerner S. Printing floating-point numbers:
a faster, always correct method. ACM SIGPLAN notices - POPL '16.
2016;51(1):555-67 <https://doi.org/10.1145/2914770.2837654>; draft at
<https://cseweb.ucsd.edu/~lerner/papers/fp-printing-popl16.pdf>. */
PROMOTED_FLOAT promoted_x = x;
char format[sizeof "%-+ 0*.*Lg"];
FLOAT abs_x = x < 0 ? -x : x;
int prec;
char *p = format;
*p++ = '%';
/* Support flags that generate output parsable by strtof. */
*p = '-'; p += (flags & FTOASTR_LEFT_JUSTIFY ) != 0;
*p = '+'; p += (flags & FTOASTR_ALWAYS_SIGNED ) != 0;
*p = ' '; p += (flags & FTOASTR_SPACE_POSITIVE) != 0;
*p = '0'; p += (flags & FTOASTR_ZERO_PAD ) != 0;
*p++ = '*';
*p++ = '.';
*p++ = '*';
*p = 'L'; p += 2 < LENGTH;
*p++ = flags & FTOASTR_UPPER_E ? 'G' : 'g';
*p = '\0';
for (prec = abs_x < FLOAT_MIN ? 1 : FLOAT_DIG; ; prec++)
{
int n = snprintf (buf, bufsize, format, width, prec, promoted_x);
if (n < 0
|| FLOAT_PREC_BOUND <= prec
|| (n < bufsize && STRTOF (buf, NULL) == x))
return n;
}
}
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