Tribblix: manual page: float.h.3head

FLOAT.H(3HEAD) Headers FLOAT.H(3HEAD)

NAME

float.h, float - floating types

SYNOPSIS

#include <float.h>

DESCRIPTION

The characteristics of floating types are defined in terms of a model
that describes a representation of floating-point numbers and values
that provide information about an implementation's floating-point
arithmetic.

The following parameters are used to define the model for each
floating-point type:

s
sign (+-1)

b
base or radix of exponent representation (an integer >1)

e
exponent (an integer between a minimum e(min) and a maximum
e(max))

p
precision (the number of base-b digits in the significand)

f(k)
non-negative integers less than b (the significand digits)

In addition to normalized floating-point numbers (f(1)>0 if x!=0),
floating types might be able to contain other kinds of floating-point
numbers, such as subnormal floating-point numbers (x!=0, e=e(min),
f(1)=0) and unnormalized floating-point numbers (x!=0, e=e(min),
f(1)=0), and values that are not floating-point numbers, such as
infinities and NaNs. A NaN is an encoding signifying Not-a-Number. A
quiet NaN propagates through almost every arithmetic operation
without raising a floating-point exception; a signaling NaN generally
raises a floating-point exception when occurring as an arithmetic
operand.

The accuracy of the library functions in math.h(3HEAD) and
complex.h(3HEAD) that return floating-point results is defined on the
libm(3LIB) manual page.

All integer values in the <float.h> header, except FLT_ROUNDS, are
constant expressions suitable for use in #if preprocessing
directives; all floating values are constant expressions. All except
DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, and FLT_ROUNDS have separate
names for all three floating-point types. The floating-point model
representation is provided for all values except FLT_EVAL_METHOD and
FLT_ROUNDS.

The rounding mode for floating-point addition is characterized by the
value of FLT_ROUNDS:

-1
Indeterminable.

0
Toward zero.

1
To nearest.

2
Toward positive infinity.

3
Toward negative infinity.

The values of operations with floating operands and values subject to
the usual arithmetic conversions and of floating constants are
evaluated to a format whose range and precision might be greater than
required by the type. The use of evaluation formats is characterized
by the architecture-dependent value of FLT_EVAL_METHOD:

-1
Indeterminable.

0
Evaluate all operations and constants just to the range and
precision of the type.

1
Evaluate operations and constants of type float and double to
the range and precision of the double type; evaluate long
double operations and constants to the range and precision of
the long double type.

2
Evaluate all operations and constants to the range and
precision of the long double type.

The values given in the following list are defined as constants.

o Radix of exponent representation, b.

FLT_RADIX

o Number of base-FLT_RADIX digits in the floating-point
significand, p.

FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG

o Number of decimal digits, n, such that any floating-point
number in the widest supported floating type with p(max)
radix b digits can be rounded to a floating-point number
with n decimal digits and back again without change to the
value.

DECIMAL_DIG

o Number of decimal digits, q, such that any floating-point
number with q decimal digits can be rounded into a
floating-point number with p radix b digits and back again
without change to the q decimal digits.

FLT_DIG
DBL_DIG
LDBL_DIG

o Minimum negative integer such that FLT_RADIX raised to
that power minus 1 is a normalized floating-point number,
e(min).

FLT_MIN_EXP
DBL_MIN_EXP
LDBL_MIN_EXP

o Minimum negative integer such that 10 raised to that power
is in the range of normalized floating-point numbers.

FLT_MIN_10_EXP
DBL_MIN_10_EXP
LDBL_MIN_10_EXP

o Maximum integer such that FLT_RADIX raised to that power
minus 1 is a representable finite floating-point number,
e(max).

FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP

o Maximum integer such that 10 raised to that power is in
the range of representable finite floating-point numbers.

FLT_MAX_10_EXP
DBL_MAX_10_EXP
LDBL_MAX_10_EXP

The values given in the following list are defined as constant
expressions with values that are greater than or equal to those
shown:

o Maximum representable finite floating-point number.

FLT_MAX
DBL_MAX
LDBL_MAX

The values given in the following list are defined as constant
expressions with implementation-defined (positive) values that are
less than or equal to those shown:

o The difference between 1 and the least value greater than
1 that is representable in the given floating-point type,
b^1 - p.

FLT_EPSILON
DBL_EPSILON
LDBL_EPSILON

o Minimum normalized positive floating-point number,
b^e(min)^-1.

FLT_MIN
DBL_MIN
LDBL_MIN

ATTRIBUTES

NAME

SYNOPSIS

DESCRIPTION

ATTRIBUTES

SEE ALSO