Content-type: text/html Man page of float.h

float.h

Section: Headers (3HEAD)
Updated: 17 Dec 2003
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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 emin and a maximum emax)

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

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

In addition to normalized floating-point numbers (f1>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=emin, f1=0) and unnormalized floating-point numbers (x≠0, e=emin, f1=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.

• Radix of exponent representation, b.

FLT_RADIX

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

FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG

• Number of decimal digits, n, such that any floating-point number in the widest supported floating type with pmax 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

• 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

• Minimum negative integer such that FLT_RADIX raised to that power minus 1 is a normalized floating-point number, emin.

FLT_MIN_EXP
DBL_MIN_EXP
LDBL_MIN_EXP

• 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

• Maximum integer such that FLT_RADIX raised to that power minus 1 is a representable finite floating-point number, emax.

FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP

• 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:

• 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:

• 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

• Minimum normalized positive floating-point number, b **emin **-1 .

FLT_MIN
DBL_MIN
LDBL_MIN

 

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPEATTRIBUTE VALUE
Interface StabilityStandard

 

SEE ALSO

complex.h(3HEAD), math.h(3HEAD), attributes(5), standards(5)


 

Index

NAME
SYNOPSIS
DESCRIPTION
ATTRIBUTES
SEE ALSO

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Time: 02:37:12 GMT, October 02, 2010