These macro definitions can be accessed by including the header file
float.h in your program.

Macro names starting with `FLT_' refer to the float type,
while names beginning with `DBL_' refer to the double type
and names beginning with `LDBL_' refer to the long double
type. (If GCC does not support long double as a distinct data
type on a target machine then the values for the `LDBL_' constants
are equal to the corresponding constants for the double type.)

Of these macros, only FLT_RADIX is guaranteed to be a constant
expression. The other macros listed here cannot be reliably used in
places that require constant expressions, such as `#if'
preprocessing directives or in the dimensions of static arrays.

Although the ISO C standard specifies minimum and maximum values for
most of these parameters, the GNU C implementation uses whatever values
describe the floating point representation of the target machine. So in
principle GNU C actually satisfies the ISO C requirements only if the
target machine is suitable. In practice, all the machines currently
supported are suitable.

FLT_ROUNDS

This value characterizes the rounding mode for floating point addition.
The following values indicate standard rounding modes:

-1

The mode is indeterminable.

0

Rounding is towards zero.

1

Rounding is to the nearest number.

2

Rounding is towards positive infinity.

3

Rounding is towards negative infinity.

Any other value represents a machine-dependent nonstandard rounding
mode.

On most machines, the value is 1, in accordance with the IEEE
standard for floating point.

Here is a table showing how certain values round for each possible value
of FLT_ROUNDS, if the other aspects of the representation match
the IEEE single-precision standard.

This is the value of the base, or radix, of the exponent representation.
This is guaranteed to be a constant expression, unlike the other macros
described in this section. The value is 2 on all machines we know of
except the IBM 360 and derivatives.

FLT_MANT_DIG

This is the number of base-FLT_RADIX digits in the floating point
mantissa for the float data type. The following expression
yields 1.0 (even though mathematically it should not) due to the
limited number of mantissa digits:

This is the number of base-FLT_RADIX digits in the floating point
mantissa for the data types double and long double,
respectively.

FLT_DIG

This is the number of decimal digits of precision for the float
data type. Technically, if p and b are the precision and
base (respectively) for the representation, then the decimal precision
q is the maximum number of decimal digits such that any floating
point number with q base 10 digits can be rounded to a floating
point number with p base b digits and back again, without
change to the q decimal digits.

The value of this macro is supposed to be at least 6, to satisfy
ISO C.

DBL_DIG

LDBL_DIG

These are similar to FLT_DIG, but for the data types
double and long double, respectively. The values of these
macros are supposed to be at least 10.

FLT_MIN_EXP

This is the smallest possible exponent value for type float.
More precisely, is the minimum negative integer such that the value
FLT_RADIX raised to this power minus 1 can be represented as a
normalized floating point number of type float.

DBL_MIN_EXP

LDBL_MIN_EXP

These are similar to FLT_MIN_EXP, but for the data types
double and long double, respectively.

FLT_MIN_10_EXP

This is the minimum negative integer such that 10 raised to this
power minus 1 can be represented as a normalized floating point number
of type float. This is supposed to be -37 or even less.

DBL_MIN_10_EXP

LDBL_MIN_10_EXP

These are similar to FLT_MIN_10_EXP, but for the data types
double and long double, respectively.

FLT_MAX_EXP

This is the largest possible exponent value for type float. More
precisely, this is the maximum positive integer such that value
FLT_RADIX raised to this power minus 1 can be represented as a
floating point number of type float.

DBL_MAX_EXP

LDBL_MAX_EXP

These are similar to FLT_MAX_EXP, but for the data types
double and long double, respectively.

FLT_MAX_10_EXP

This is the maximum positive integer such that 10 raised to this
power minus 1 can be represented as a normalized floating point number
of type float. This is supposed to be at least 37.

DBL_MAX_10_EXP

LDBL_MAX_10_EXP

These are similar to FLT_MAX_10_EXP, but for the data types
double and long double, respectively.

FLT_MAX

The value of this macro is the maximum number representable in type
float. It is supposed to be at least 1E+37. The value
has type float.

The smallest representable number is - FLT_MAX.

DBL_MAX

LDBL_MAX

These are similar to FLT_MAX, but for the data types
double and long double, respectively. The type of the
macro's value is the same as the type it describes.

FLT_MIN

The value of this macro is the minimum normalized positive floating
point number that is representable in type float. It is supposed
to be no more than 1E-37.

DBL_MIN

LDBL_MIN

These are similar to FLT_MIN, but for the data types
double and long double, respectively. The type of the
macro's value is the same as the type it describes.

FLT_EPSILON

This is the maximum positive floating point number of type float
such that 1.0 + FLT_EPSILON != 1.0 is true. It's supposed to
be no greater than 1E-5.

DBL_EPSILON

LDBL_EPSILON

These are similar to FLT_EPSILON, but for the data types
double and long double, respectively. The type of the
macro's value is the same as the type it describes. The values are not
supposed to be greater than 1E-9.

Published under the terms of the GNU General Public License