float.h (3head) manual page
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:
tab() allbox; cw(2.750000i)| cw(2.750000i) lw(2.750000i) lw(2.750000i). ATTRIBUTE TYPEATTRIBUTE VALUE Interface StabilityStandard
See Also
complex.h(3HEAD) , math.h(3HEAD) , attributes(5) , standards(5)
