Originální popis anglicky:
float.h  floating types
Návod, kniha: POSIX Programmer's Manual
#include <float.h>
The characteristics of floating types are defined in terms of a model that
describes a representation of floatingpoint numbers and values that provide
information about an implementation's floatingpoint arithmetic.
The following parameters are used to define the model for each floatingpoint
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 baseb digits in the
significand).
 f_k
 Nonnegative integers less than b (the significand
digits).
A floatingpoint number
x is defined by the following model:
In addition to normalized floatingpoint numbers (
f_1>0 if
x!=0), floating types may be able to contain other kinds of
floatingpoint numbers, such as subnormal floatingpoint numbers (
x!=0,
e=
e_min,
f_1=0) and unnormalized
floatingpoint numbers (
x!=0,
e>
e_min,
f_1=0), and values that are not floatingpoint numbers, such as
infinities and NaNs. A
NaN is an encoding signifying NotaNumber. A
quiet NaN propagates through almost every arithmetic operation without
raising a floatingpoint exception; a
signaling NaN generally raises a
floatingpoint exception when occurring as an arithmetic operand.
The accuracy of the floatingpoint operations (
'+' ,
'' ,
'*' ,
'/' ) and of the library functions in
<math.h> and
<complex.h> that return floatingpoint
results is implementationdefined. 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
DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, and FLT_ROUNDS have separate names
for all three floatingpoint types. The floatingpoint model representation is
provided for all values except FLT_EVAL_METHOD and FLT_ROUNDS.
The rounding mode for floatingpoint addition is characterized by the
implementationdefined 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 implementationdefined 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 implementationdefined 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.
All other negative values for FLT_EVAL_METHOD characterize
implementationdefined behavior.
The values given in the following list shall be defined as constant expressions
with implementationdefined 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 baseFLT_RADIX digits in the floatingpoint
significand, p.
 FLT_MANT_DIG
 DBL_MANT_DIG
 LDBL_MANT_DIG

 *
 Number of decimal digits, n, such that any
floatingpoint number in the widest supported floating type with
p_max radix b digits can be rounded to a floatingpoint
number with n decimal digits and back again without change to the
value.
 DECIMAL_DIG
10
 *
 Number of decimal digits, q, such that any
floatingpoint number with q decimal digits can be rounded into a
floatingpoint 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 floatingpoint 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 floatingpoint 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 floatingpoint 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 floatingpoint 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 implementationdefined values that are greater than or equal to those
shown:
 *
 Maximum representable finite floatingpoint 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 implementationdefined (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 floatingpoint type,
b**1p.
 FLT_EPSILON
1E5
 DBL_EPSILON
1E9
 LDBL_EPSILON
1E9
 *
 Minimum normalized positive floatingpoint number,
b** e_min.
 FLT_MIN
1E37
 DBL_MIN
1E37
 LDBL_MIN
1E37
The following sections are informative.
None.
None.
None.
<complex.h> ,
<math.h>
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) 20012003 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
.