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Linux 2.6 - man page for float.h (linux section 7posix)

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

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 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).

       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 infinities and NaNs. A NaN
       is an encoding signifying Not-a-Number. A quiet NaN propagates through almost every arith-
       metic 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 floating-point operations ( '+' , '-' , '*' , '/' ) and of the library
       functions in <math.h> and <complex.h> that return floating-point  results  is  implementa-
       tion-defined. The implementation may state that the accuracy is unknown.

       All  integer  values in the <float.h> header, except FLT_ROUNDS, shall be constant expres-
       sions suitable for use in #if preprocessing directives; all floating values shall be  con-
       stant 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 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 evaluated 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 precision of the type.

	1     Evaluate	operations and constants of type float and double to the range and preci-
	      sion 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  implementation-defined  behav-
       ior.

       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 sup-
	  ported floating type with p_max radix b digits can be rounded to a floating-point  num-
	  ber 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  with-
	  out 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 normal-
	  ized 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  normal-
	  ized 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 orig-
       inal 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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