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

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

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>(P)
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