163 lines
6.4 KiB
C
163 lines
6.4 KiB
C
/* floating point to accurate string
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Copyright (C) 2010-2024 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 <https://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert. */
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#ifndef _GL_FTOASTR_H
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#define _GL_FTOASTR_H
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#include "intprops.h"
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#include <float.h>
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#include <stddef.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Store into BUF (of size BUFSIZE) an accurate minimal-precision
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string representation of a floating point number. FLAGS affect the
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formatting of the number. Pad the output string with spaces as
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necessary to width WIDTH bytes, in the style of printf. WIDTH must
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be nonnegative. X is the floating-point number to be converted.
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Return the number of bytes stored into BUF, not counting the
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terminating null. However, do not overrun BUF: if BUF is too
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small, return a fairly tight (but not necessarily exact) upper
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bound on the value that would have been returned if BUF had been
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big enough. If SIZE is zero, BUF may be a null pointer. On error
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(e.g., returned value would exceed INT_MAX), return -1 and set
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errno.
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Example:
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char buf[DBL_BUFSIZE_BOUND];
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int r = dtoastr (buf, sizeof buf, 0, 0, 0.1);
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In the C locale, this sets R to 3 and stores "0.1" into BUF. */
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int ftoastr (char *buf, size_t bufsize, int flags, int width, float x);
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int dtoastr (char *buf, size_t bufsize, int flags, int width, double x);
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int ldtoastr (char *buf, size_t bufsize, int flags, int width, long double x);
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/* The last two functions except that the formatting takes place in
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the C locale. */
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int c_dtoastr (char *buf, size_t bufsize, int flags, int width, double x);
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int c_ldtoastr (char *buf, size_t bufsize, int flags, int width, long double x);
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/* Flag values for ftoastr etc. These can be ORed together. */
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enum
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{
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/* Left justify within the width; the default is right justification. */
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FTOASTR_LEFT_JUSTIFY = 1,
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/* Output "+" before positive numbers; the default outputs nothing. */
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FTOASTR_ALWAYS_SIGNED = 2,
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/* Output " " before positive numbers; ignored if
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FTOASTR_ALWAYS_SIGNED is also given. */
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FTOASTR_SPACE_POSITIVE = 4,
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/* Pad with zeros instead of spaces; ignored if FTOASTR_LEFT_JUSTIFY
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is also given. */
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FTOASTR_ZERO_PAD = 8,
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/* Use 'E' instead of 'e' before the exponent. */
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FTOASTR_UPPER_E = 16
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};
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/* _GL_FLT_PREC_BOUND is an upper bound on the precision needed to
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represent a float value without losing information. Likewise for
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_GL_DBL_PREC_BOUND and double, and _GL_LDBL_PREC_BOUND and long double.
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These are macros, not enums, to work around a bug in IBM xlc 12.1. */
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#if FLT_RADIX == 10 /* decimal floating point */
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# define _GL_FLT_PREC_BOUND FLT_MANT_DIG
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# define _GL_DBL_PREC_BOUND DBL_MANT_DIG
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# define _GL_LDBL_PREC_BOUND LDBL_MANT_DIG
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#else
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/* An upper bound on the number of bits needed to represent a single
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digit in a floating-point fraction. */
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# if FLT_RADIX == 2 /* IEEE 754 floating point, VAX floating point, etc. */
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# define _GL_FLOAT_DIG_BITS_BOUND 1
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# elif FLT_RADIX <= 16 /* IBM hex floating point has FLT_RADIX == 16. */
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# define _GL_FLOAT_DIG_BITS_BOUND 4
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# else /* no machine is this bad, but let's be complete */
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# define _GL_FLOAT_DIG_BITS_BOUND ((int) TYPE_WIDTH (int) - 1)
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# endif
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/* An upper bound on the number of decimal digits needed to represent
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a floating point number accurately, assuming a fraction contains
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DIG digits. For why the "+ 1" is needed, see "Binary to Decimal
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Conversion" in David Goldberg's paper "What Every Computer
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Scientist Should Know About Floating-Point Arithmetic"
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<https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html>. */
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# define _GL_FLOAT_PREC_BOUND(dig) \
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(INT_BITS_STRLEN_BOUND ((dig) * _GL_FLOAT_DIG_BITS_BOUND) + 1)
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# define _GL_FLT_PREC_BOUND _GL_FLOAT_PREC_BOUND ( FLT_MANT_DIG)
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# define _GL_DBL_PREC_BOUND _GL_FLOAT_PREC_BOUND ( DBL_MANT_DIG)
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# define _GL_LDBL_PREC_BOUND _GL_FLOAT_PREC_BOUND (LDBL_MANT_DIG)
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#endif
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/* Bound on the number of bytes printed for an exponent in the range
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MIN..MAX, where MIN < 0 < MAX; printf always prints a sign and at
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least 2 digits. Although the maximum known exponent is 4932 for
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IEEE 754 binary128, support tight bounds for exponents up to a
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million, just in case. */
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#define _GL_FLOAT_EXPONENT_STRLEN_BOUND(min, max) \
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( -100 < (min) && (max) < 100 ? 3 \
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: -1000 < (min) && (max) < 1000 ? 4 \
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: -10000 < (min) && (max) < 10000 ? 5 \
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: -100000 < (min) && (max) < 100000 ? 6 \
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: -1000000 < (min) && (max) < 1000000 ? 7 \
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: INT_STRLEN_BOUND (int) /* not a tight bound */)
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/* A reasonably tight bound on the length of a type-T floating value
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formatted with ftoastr etc. Room is needed for sign, fraction
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digits, decimal point, "e", and exponent. POINTLEN should be a
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reasonably tight bound on the string length of the decimal
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point. */
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#define _GL_FLOAT_STRLEN_BOUND_L(t, pointlen) \
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(1 + _GL_##t##_PREC_BOUND + pointlen + 1 \
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+ _GL_FLOAT_EXPONENT_STRLEN_BOUND (t##_MIN_10_EXP, t##_MAX_10_EXP))
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#define FLT_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( FLT, pointlen)
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#define DBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L ( DBL, pointlen)
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#define LDBL_STRLEN_BOUND_L(pointlen) _GL_FLOAT_STRLEN_BOUND_L (LDBL, pointlen)
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/* Looser bounds that are locale-independent and are integral constant
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expressions. */
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#define FLT_STRLEN_BOUND FLT_STRLEN_BOUND_L (MB_LEN_MAX)
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#define DBL_STRLEN_BOUND DBL_STRLEN_BOUND_L (MB_LEN_MAX)
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#define LDBL_STRLEN_BOUND LDBL_STRLEN_BOUND_L (MB_LEN_MAX)
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/* Looser, locale-independent bounds that include the trailing null byte. */
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#define FLT_BUFSIZE_BOUND ( FLT_STRLEN_BOUND + 1)
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#define DBL_BUFSIZE_BOUND ( DBL_STRLEN_BOUND + 1)
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#define LDBL_BUFSIZE_BOUND (LDBL_STRLEN_BOUND + 1)
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#ifdef __cplusplus
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}
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#endif
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#endif /* _GL_FTOASTR_H */
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