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Diffstat (limited to 'lib/ftoastr.h')
| -rw-r--r-- | lib/ftoastr.h | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/lib/ftoastr.h b/lib/ftoastr.h new file mode 100644 index 0000000..bac32a3 --- /dev/null +++ b/lib/ftoastr.h @@ -0,0 +1,152 @@ +/* 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. */ + +#ifndef _GL_FTOASTR_H +#define _GL_FTOASTR_H + +#include "intprops.h" +#include <float.h> +#include <stddef.h> + +/* Store into BUF (of size BUFSIZE) an accurate minimal-precision + string representation of a floating point number. FLAGS affect the + formatting of the number. Pad the output string with spaces as + necessary to width WIDTH bytes, in the style of printf. WIDTH must + be nonnegative. X is the floating-point number to be converted. + + Return the number of bytes stored into BUF, not counting the + terminating null. However, do not overrun BUF: if BUF is too + small, return a fairly tight (but not necessarily exact) upper + bound on the value that would have been returned if BUF had been + big enough. If SIZE is zero, BUF may be a null pointer. On error + (e.g., returned value would exceed INT_MAX), return -1 and set + errno. + + Example: + + char buf[DBL_BUFSIZE_BOUND]; + int r = dtoastr (buf, sizeof buf, 0, 0, 0.1); + + In the C locale, this sets R to 3 and stores "0.1" into BUF. */ + +int ftoastr (char *buf, size_t bufsize, int flags, int width, float x); +int dtoastr (char *buf, size_t bufsize, int flags, int width, double x); +int ldtoastr (char *buf, size_t bufsize, int flags, int width, long double x); + +/* The last two functions except that the formatting takes place in + the C locale. */ +int c_dtoastr (char *buf, size_t bufsize, int flags, int width, double x); +int c_ldtoastr (char *buf, size_t bufsize, int flags, int width, long double x); + + +/* Flag values for ftoastr etc. These can be ORed together. */ +enum + { + /* Left justify within the width; the default is right justification. */ + FTOASTR_LEFT_JUSTIFY = 1, + + /* Output "+" before positive numbers; the default outputs nothing. */ + FTOASTR_ALWAYS_SIGNED = 2, + + /* Output " " before positive numbers; ignored if + FTOASTR_ALWAYS_SIGNED is also given. */ + FTOASTR_SPACE_POSITIVE = 4, + + /* Pad with zeros instead of spaces; ignored if FTOASTR_LEFT_JUSTIFY + is also given. */ + FTOASTR_ZERO_PAD = 8, + + /* Use 'E' instead of 'e' before the exponent. */ + FTOASTR_UPPER_E = 16 + }; + + +/* _GL_FLT_PREC_BOUND is an upper bound on the precision needed to + represent a float value without losing information. Likewise for + _GL_DBL_PREC_BOUND and double, and _GL_LDBL_PREC_BOUND and long double. + These are macros, not enums, to work around a bug in IBM xlc 12.1. */ + +#if FLT_RADIX == 10 /* decimal floating point */ +# define _GL_FLT_PREC_BOUND FLT_MANT_DIG +# define _GL_DBL_PREC_BOUND DBL_MANT_DIG +# define _GL_LDBL_PREC_BOUND LDBL_MANT_DIG +#else + +/* An upper bound on the number of bits needed to represent a single + digit in a floating-point fraction. */ +# if FLT_RADIX == 2 /* IEEE 754 floating point, VAX floating point, etc. */ +# define _GL_FLOAT_DIG_BITS_BOUND 1 +# elif FLT_RADIX <= 16 /* IBM hex floating point has FLT_RADIX == 16. */ +# define _GL_FLOAT_DIG_BITS_BOUND 4 +# else /* no machine is this bad, but let's be complete */ +# define _GL_FLOAT_DIG_BITS_BOUND ((int) TYPE_WIDTH (int) - 1) +# endif + +/* An upper bound on the number of decimal digits needed to represent + a floating point number accurately, assuming a fraction contains + DIG digits. For why the "+ 1" is needed, see "Binary to Decimal + Conversion" in David Goldberg's paper "What Every Computer + Scientist Should Know About Floating-Point Arithmetic" + <https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html>. */ +# define _GL_FLOAT_PREC_BOUND(dig) \ + (INT_BITS_STRLEN_BOUND ((dig) * _GL_FLOAT_DIG_BITS_BOUND) + 1) + +# define _GL_FLT_PREC_BOUND _GL_FLOAT_PREC_BOUND ( FLT_MANT_DIG) +# define _GL_DBL_PREC_BOUND _GL_FLOAT_PREC_BOUND ( DBL_MANT_DIG) +# define _GL_LDBL_PREC_BOUND _GL_FLOAT_PREC_BOUND (LDBL_MANT_DIG) +#endif + + +/* Bound on the number of bytes printed for an exponent in the range + MIN..MAX, where MIN < 0 < MAX; printf always prints a sign and at + least 2 digits. Although the maximum known exponent is 4932 for + IEEE 754 binary128, support tight bounds for exponents up to a + million, just in case. */ +#define _GL_FLOAT_EXPONENT_STRLEN_BOUND(min, max) \ + ( -100 < (min) && (max) < 100 ? 3 \ + : -1000 < (min) && (max) < 1000 ? 4 \ + : -10000 < (min) && (max) < 10000 ? 5 \ + : -100000 < (min) && (max) < 100000 ? 6 \ + : -1000000 < (min) && (max) < 1000000 ? 7 \ + : INT_STRLEN_BOUND (int) /* not a tight bound */) + +/* A reasonably tight bound on the length of a type-T floating value + formatted with ftoastr etc. Room is needed for sign, fraction + digits, decimal point, "e", and exponent. POINTLEN should be a + reasonably tight bound on the string length of the decimal + point. */ +#define _GL_FLOAT_STRLEN_BOUND_L(t, pointlen) \ + (1 + _GL_##t##_PREC_BOUND + pointlen + 1 \ + + _GL_FLOAT_EXPONENT_STRLEN_BOUND (t##_MIN_10_EXP, t##_MAX_10_EXP)) +#define FLT_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( FLT, pointlen) +#define DBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( DBL, pointlen) +#define LDBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L (LDBL, pointlen) + +/* Looser bounds that are locale-independent and are integral constant + expressions. */ +#define FLT_STRLEN_BOUND FLT_STRLEN_BOUND_L (MB_LEN_MAX) +#define DBL_STRLEN_BOUND DBL_STRLEN_BOUND_L (MB_LEN_MAX) +#define LDBL_STRLEN_BOUND LDBL_STRLEN_BOUND_L (MB_LEN_MAX) + +/* Looser, locale-independent bounds that include the trailing null byte. */ +#define FLT_BUFSIZE_BOUND ( FLT_STRLEN_BOUND + 1) +#define DBL_BUFSIZE_BOUND ( DBL_STRLEN_BOUND + 1) +#define LDBL_BUFSIZE_BOUND (LDBL_STRLEN_BOUND + 1) + +#endif /* _GL_FTOASTR_H */ |