| 1 | /* floating point to accurate string |
| 2 | |
| 3 | Copyright (C) 2010-2013 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 | #ifndef _GL_FTOASTR_H |
| 21 | |
| 22 | #include "intprops.h" |
| 23 | #include <float.h> |
| 24 | #include <stddef.h> |
| 25 | |
| 26 | /* Store into BUF (of size BUFSIZE) an accurate minimal-precision |
| 27 | string representation of a floating point number. FLAGS affect the |
| 28 | formatting of the number. Pad the output string with spaces as |
| 29 | necessary to width WIDTH bytes, in the style of printf. WIDTH must |
| 30 | be nonnegative. X is the floating-point number to be converted. |
| 31 | |
| 32 | Return the number of bytes stored into BUF, not counting the |
| 33 | terminating null. However, do not overrun BUF: if BUF is too |
| 34 | small, return a fairly tight (but not necessarily exact) upper |
| 35 | bound on the value that would have been returned if BUF had been |
| 36 | big enough. If SIZE is zero, BUF may be a null pointer. On error |
| 37 | (e.g., returned value would exceed INT_MAX), return -1 and set |
| 38 | errno. |
| 39 | |
| 40 | Example: |
| 41 | |
| 42 | char buf[DBL_BUFSIZE_BOUND]; |
| 43 | int r = dtoastr (buf, sizeof buf, 0, 0, 0.1); |
| 44 | |
| 45 | In the C locale, this sets R to 3 and stores "0.1" into BUF. */ |
| 46 | |
| 47 | int ftoastr (char *buf, size_t bufsize, int flags, int width, float x); |
| 48 | int dtoastr (char *buf, size_t bufsize, int flags, int width, double x); |
| 49 | int ldtoastr (char *buf, size_t bufsize, int flags, int width, long double x); |
| 50 | |
| 51 | /* Flag values for ftoastr etc. These can be ORed together. */ |
| 52 | enum |
| 53 | { |
| 54 | /* Left justify within the width; the default is right justification. */ |
| 55 | FTOASTR_LEFT_JUSTIFY = 1, |
| 56 | |
| 57 | /* Output "+" before positive numbers; the default outputs nothing. */ |
| 58 | FTOASTR_ALWAYS_SIGNED = 2, |
| 59 | |
| 60 | /* Output " " before positive numbers; ignored if |
| 61 | FTOASTR_ALWAYS_SIGNED is also given. */ |
| 62 | FTOASTR_SPACE_POSITIVE = 4, |
| 63 | |
| 64 | /* Pad with zeros instead of spaces; ignored if FTOASTR_LEFT_JUSTIFY |
| 65 | is also given. */ |
| 66 | FTOASTR_ZERO_PAD = 8, |
| 67 | |
| 68 | /* Use 'E' instead of 'e' before the exponent. */ |
| 69 | FTOASTR_UPPER_E = 16 |
| 70 | }; |
| 71 | |
| 72 | |
| 73 | /* _GL_FLT_PREC_BOUND is an upper bound on the precision needed to |
| 74 | represent a float value without losing information. Likewise for |
| 75 | _GL_DBL_PREC_BOUND and double, and _GL_LDBL_PREC_BOUND and long double. */ |
| 76 | |
| 77 | #if FLT_RADIX == 10 /* decimal floating point */ |
| 78 | enum { _GL_FLT_PREC_BOUND = FLT_MANT_DIG }; |
| 79 | enum { _GL_DBL_PREC_BOUND = DBL_MANT_DIG }; |
| 80 | enum { _GL_LDBL_PREC_BOUND = LDBL_MANT_DIG }; |
| 81 | #else |
| 82 | |
| 83 | /* An upper bound on the number of bits needed to represent a single |
| 84 | digit in a floating-point fraction. */ |
| 85 | # if FLT_RADIX == 2 /* IEEE 754 floating point, VAX floating point, etc. */ |
| 86 | # define _GL_FLOAT_DIG_BITS_BOUND 1 |
| 87 | # elif FLT_RADIX <= 16 /* IBM hex floating point has FLT_RADIX == 16. */ |
| 88 | # define _GL_FLOAT_DIG_BITS_BOUND 4 |
| 89 | # else /* no machine is this bad, but let's be complete */ |
| 90 | # define _GL_FLOAT_DIG_BITS_BOUND (CHAR_BIT * (int) sizeof (int) - 1) |
| 91 | # endif |
| 92 | |
| 93 | /* An upper bound on the number of decimal digits needed to represent |
| 94 | a floating point number accurately, assuming a fraction contains |
| 95 | DIG digits. For why the "+ 1" is needed, see "Binary to Decimal |
| 96 | Conversion" in David Goldberg's paper "What Every Computer |
| 97 | Scientist Should Know About Floating-Point Arithmetic" |
| 98 | <http://docs.sun.com/source/806-3568/ncg_goldberg.html>. */ |
| 99 | # define _GL_FLOAT_PREC_BOUND(dig) \ |
| 100 | (INT_BITS_STRLEN_BOUND ((dig) * _GL_FLOAT_DIG_BITS_BOUND) + 1) |
| 101 | |
| 102 | enum { _GL_FLT_PREC_BOUND = _GL_FLOAT_PREC_BOUND ( FLT_MANT_DIG) }; |
| 103 | enum { _GL_DBL_PREC_BOUND = _GL_FLOAT_PREC_BOUND ( DBL_MANT_DIG) }; |
| 104 | enum { _GL_LDBL_PREC_BOUND = _GL_FLOAT_PREC_BOUND (LDBL_MANT_DIG) }; |
| 105 | #endif |
| 106 | |
| 107 | |
| 108 | /* Bound on the number of bytes printed for an exponent in the range |
| 109 | MIN..MAX, where MIN < 0 < MAX; printf always prints a sign and at |
| 110 | least 2 digits. Although the maximum known exponent is 4932 for |
| 111 | IEEE 754 binary128, support tight bounds for exponents up to a |
| 112 | million, just in case. */ |
| 113 | #define _GL_FLOAT_EXPONENT_STRLEN_BOUND(min, max) \ |
| 114 | ( -100 < (min) && (max) < 100 ? 3 \ |
| 115 | : -1000 < (min) && (max) < 1000 ? 4 \ |
| 116 | : -10000 < (min) && (max) < 10000 ? 5 \ |
| 117 | : -100000 < (min) && (max) < 100000 ? 6 \ |
| 118 | : -1000000 < (min) && (max) < 1000000 ? 7 \ |
| 119 | : INT_STRLEN_BOUND (int) /* not a tight bound */) |
| 120 | |
| 121 | /* A reasonably tight bound on the length of a type-T floating value |
| 122 | formatted with ftoastr etc. Room is needed for sign, fraction |
| 123 | digits, decimal point, "e", and exponent. POINTLEN should be a |
| 124 | reasonably tight bound on the string length of the decimal |
| 125 | point. */ |
| 126 | #define _GL_FLOAT_STRLEN_BOUND_L(t, pointlen) \ |
| 127 | (1 + _GL_##t##_PREC_BOUND + pointlen + 1 \ |
| 128 | + _GL_FLOAT_EXPONENT_STRLEN_BOUND (t##_MIN_10_EXP, t##_MAX_10_EXP)) |
| 129 | #define FLT_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( FLT, pointlen) |
| 130 | #define DBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( DBL, pointlen) |
| 131 | #define LDBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L (LDBL, pointlen) |
| 132 | |
| 133 | /* Looser bounds that are locale-independent and are integral constant |
| 134 | expressions. */ |
| 135 | #define FLT_STRLEN_BOUND FLT_STRLEN_BOUND_L (MB_LEN_MAX) |
| 136 | #define DBL_STRLEN_BOUND DBL_STRLEN_BOUND_L (MB_LEN_MAX) |
| 137 | #define LDBL_STRLEN_BOUND LDBL_STRLEN_BOUND_L (MB_LEN_MAX) |
| 138 | |
| 139 | /* Looser, locale-independent bounds that include the trailing null byte. */ |
| 140 | #define FLT_BUFSIZE_BOUND ( FLT_STRLEN_BOUND + 1) |
| 141 | #define DBL_BUFSIZE_BOUND ( DBL_STRLEN_BOUND + 1) |
| 142 | #define LDBL_BUFSIZE_BOUND (LDBL_STRLEN_BOUND + 1) |
| 143 | |
| 144 | #endif /* _GL_FTOASTR_H */ |