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<float.h>(0P)		   POSIX Programmer's Manual		 <float.h>(0P)

NAME
       float.h - 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	float‐
       ing-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).

       A floating-point number x is defined by the following model:

       In addition to  normalized  floating-point  numbers  (f_1>0  if	x!=0),
       floating	 types	may  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 infini‐
       ties  and  NaNs.	 A NaN is an encoding signifying Not-a-Number. A quiet
       NaN propagates through almost every arithmetic operation without	 rais‐
       ing  a  floating-point  exception;  a  signaling NaN generally raises a
       floating-point exception when occurring as an arithmetic operand.

       The accuracy of the floating-point operations ( '+', '-',  '*',	'/'  )
       and  of	the  library functions in <math.h> and <complex.h> that return
       floating-point results is  implementation-defined.  The	implementation
       may state that the accuracy is unknown.

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

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

       -1     Indeterminable.

	0     Toward zero.

	1     To nearest.

	2     Toward positive infinity.

	3     Toward negative infinity.

       All other values	 for  FLT_ROUNDS  characterize	implementation-defined
       rounding behavior.

       The  values  of operations with floating operands and values subject to
       the usual arithmetic conversions and of floating constants  are	evalu‐
       ated to a format whose range and precision may be greater than required
       by the type. The use of evaluation  formats  is	characterized  by  the
       implementation-defined value of FLT_EVAL_METHOD:

       -1     Indeterminable.

	0     Evaluate all operations and constants just to the range and pre‐
	      cision 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.

       All other negative values for FLT_EVAL_METHOD characterize  implementa‐
       tion-defined behavior.

       The  values  given  in  the following list shall be defined as constant
       expressions with implementation-defined	values	that  are  greater  or
       equal in magnitude (absolute value) to those shown, with the same sign.

	* Radix of exponent representation, b.

       FLT_RADIX
	      2

	* 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 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
	      10

	* 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
	      6

       DBL_DIG
	      10

       LDBL_DIG
	      10

	* 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

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

       FLT_MIN_10_EXP
	      -37

       DBL_MIN_10_EXP
	      -37

       LDBL_MIN_10_EXP
	      -37

	* 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

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

       FLT_MAX_10_EXP
	      +37

       DBL_MAX_10_EXP
	      +37

       LDBL_MAX_10_EXP
	      +37

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

	* Maximum representable finite floating-point number.

       FLT_MAX
	      1E+37

       DBL_MAX
	      1E+37

       LDBL_MAX
	      1E+37

       The values given in the following list shall  be	 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
	      1E-5

       DBL_EPSILON
	      1E-9

       LDBL_EPSILON
	      1E-9

	* Minimum normalized positive floating-point number, b**e_min.

       FLT_MIN
	      1E-37

       DBL_MIN
	      1E-37

       LDBL_MIN
	      1E-37

       The following sections are informative.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <complex.h>, <math.h>

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	by  the	 Institute  of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained	online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			 <float.h>(0P)
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