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Diffstat (limited to 'lib/ftoastr.c')
| -rw-r--r-- | lib/ftoastr.c | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/lib/ftoastr.c b/lib/ftoastr.c new file mode 100644 index 0000000..9105752 --- /dev/null +++ b/lib/ftoastr.c @@ -0,0 +1,151 @@ +/* floating point to accurate string + + Copyright (C) 2010-2022 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; + } +} |