dtoa.h File Reference

#include <cfloat>
#include <cstddef>
#include "mysql/strings/api.h"

Go to the source code of this file.

Macros
#define	MAX_DECPT_FOR_F_FORMAT   DBL_DIG
#define	MY_GCVT_MAX_FIELD_WIDTH    (DBL_DIG + 4 + std::max(5, MAX_DECPT_FOR_F_FORMAT))

Enumerations
enum	my_gcvt_arg_type { MY_GCVT_ARG_FLOAT , MY_GCVT_ARG_DOUBLE }

Functions
MYSQL_STRINGS_EXPORT double	my_strtod (const char *str, const char **end, int *error)
	Converts string to double (string does not have to be zero-terminated) More...
MYSQL_STRINGS_EXPORT size_t	my_fcvt (double x, int precision, char *to, bool *error)
	Converts a given floating point number to a zero-terminated string representation using the 'f' format. More...
MYSQL_STRINGS_EXPORT size_t	my_fcvt_compact (double x, char *to, bool *error)
	Converts a given floating point number to a zero-terminated string representation using the 'f' format. More...
MYSQL_STRINGS_EXPORT size_t	my_gcvt (double x, my_gcvt_arg_type type, int width, char *to, bool *error)
	Converts a given floating point number to a zero-terminated string representation with a given field width using the 'e' format (aka scientific notation) or the 'f' one. More...

Variables
static constexpr int	DECIMAL_MAX_SCALE {30}
static constexpr int	DECIMAL_NOT_SPECIFIED {DECIMAL_MAX_SCALE + 1}
static constexpr int	FLOATING_POINT_BUFFER {311 + DECIMAL_NOT_SPECIFIED}

Macro Definition Documentation

MAX_DECPT_FOR_F_FORMAT

#define MAX_DECPT_FOR_F_FORMAT   DBL_DIG

MY_GCVT_MAX_FIELD_WIDTH

#define MY_GCVT_MAX_FIELD_WIDTH    (DBL_DIG + 4 + std::max(5, MAX_DECPT_FOR_F_FORMAT))

Enumeration Type Documentation

my_gcvt_arg_type

enum my_gcvt_arg_type

Enumerator
MY_GCVT_ARG_FLOAT
MY_GCVT_ARG_DOUBLE

Function Documentation

my_fcvt()

MYSQL_STRINGS_EXPORT size_t my_fcvt	(	double	x,
		int	precision,
		char *	to,
		bool *	error
	)

Converts a given floating point number to a zero-terminated string representation using the 'f' format.

This function is a wrapper around dtoa() to do the same as sprintf(to, "%-.*f", precision, x), though the conversion is usually more precise. The only difference is in handling [-,+]infinity and nan values, in which case we print '0\0' to the output string and indicate an overflow.

Parameters

x	the input floating point number.
precision	the number of digits after the decimal point. All properties of sprintf() apply: if the number of significant digits after the decimal point is less than precision, the resulting string is right-padded with zeros if the precision is 0, no decimal point appears if a decimal point appears, at least one digit appears before it
to	pointer to the output buffer. The longest string which my_fcvt() can return is FLOATING_POINT_BUFFER bytes (including the terminating '\0').
error	if not NULL, points to a location where the status of conversion is stored upon return. false successful conversion true the input number is [-,+]infinity or nan. The output string in this case is always '0'.

Returns

number of written characters (excluding terminating '\0')

my_fcvt_compact()

MYSQL_STRINGS_EXPORT size_t my_fcvt_compact	(	double	x,
		char *	to,
		bool *	error
	)

Converts a given floating point number to a zero-terminated string representation using the 'f' format.

This function is a wrapper around dtoa() to do almost the same as sprintf(to, "%-.*f", precision, x), though the conversion is usually more precise. The only difference is in handling [-,+]infinity and nan values, in which case we print '0\0' to the output string and indicate an overflow.

The string always contains the minimum number of digits necessary to reproduce the same binary double value if the string is parsed back to a double value.

Parameters

x	the input floating point number.
to	pointer to the output buffer. The longest string which my_fcvt() can return is FLOATING_POINT_BUFFER bytes (including the terminating '\0').
error	if not NULL, points to a location where the status of conversion is stored upon return. false successful conversion true the input number is [-,+]infinity or nan. The output string in this case is always '0'.

Returns

number of written characters (excluding terminating '\0')

my_gcvt()

MYSQL_STRINGS_EXPORT size_t my_gcvt	(	double	x,
		my_gcvt_arg_type	type,
		int	width,
		char *	to,
		bool *	error
	)

Converts a given floating point number to a zero-terminated string representation with a given field width using the 'e' format (aka scientific notation) or the 'f' one.

The format is chosen automatically to provide the most number of significant digits (and thus, precision) with a given field width. In many cases, the result is similar to that of sprintf(to, "%g", x) with a few notable differences:

• the conversion is usually more precise than C library functions.
• there is no 'precision' argument. instead, we specify the number of characters available for conversion (i.e. a field width).
• the result never exceeds the specified field width. If the field is too short to contain even a rounded decimal representation, my_gcvt() indicates overflow and truncates the output string to the specified width.
• float-type arguments are handled differently than double ones. For a float input number (i.e. when the 'type' argument is MY_GCVT_ARG_FLOAT) we deliberately limit the precision of conversion by FLT_DIG digits to avoid garbage past the significant digits.
• unlike sprintf(), in cases where the 'e' format is preferred, we don't zero-pad the exponent to save space for significant digits. The '+' sign for a positive exponent does not appear for the same reason.

Parameters

x	the input floating point number.
type	is either MY_GCVT_ARG_FLOAT or MY_GCVT_ARG_DOUBLE. Specifies the type of the input number (see notes above).
width	field width in characters. The minimal field width to hold any number representation (albeit rounded) is 7 characters ("-Ne-NNN").
to	pointer to the output buffer. The result is always zero-terminated, and the longest returned string is thus 'width + 1' bytes.
error	if not NULL, points to a location where the status of conversion is stored upon return. false successful conversion true the input number is [-,+]infinity or nan. The output string in this case is always '0'.

Returns

number of written characters (excluding terminating '\0')

my_gcvt(-9e-3, ..., 4, ...); my_gcvt(-9e-3, ..., 2, ...); my_gcvt(1.87e-3, ..., 4, ...); my_gcvt(55, ..., 1, ...);

We do our best to minimize such cases by:

• passing to dtoa() the field width as the number of significant digits
• removing the sign of the number early (and decreasing the width before passing it to dtoa())
• choosing the proper format to preserve the most number of significant digits.

my_strtod()

MYSQL_STRINGS_EXPORT double my_strtod	(	const char *	str,
		const char **	end,
		int *	error
	)

Converts string to double (string does not have to be zero-terminated)

This is a wrapper around dtoa's version of strtod().

Parameters

str	input string
end	address of a pointer to the first character after the input string. Upon return the pointer is set to point to the first rejected character.
error	Upon return is set to EOVERFLOW in case of underflow or overflow.

Returns

The resulting double value. In case of underflow, 0.0 is returned. In case overflow, signed DBL_MAX is returned.

Variable Documentation

DECIMAL_MAX_SCALE

constexpr int DECIMAL_MAX_SCALE {30}

staticconstexpr

DECIMAL_NOT_SPECIFIED

constexpr int DECIMAL_NOT_SPECIFIED {DECIMAL_MAX_SCALE + 1}

staticconstexpr

FLOATING_POINT_BUFFER

constexpr int FLOATING_POINT_BUFFER {311 + DECIMAL_NOT_SPECIFIED}

staticconstexpr