| <html lang="en"> |
| <head> |
| <title>Floating Point Parameters - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Floating-Type-Macros.html#Floating-Type-Macros" title="Floating Type Macros"> |
| <link rel="prev" href="Floating-Point-Concepts.html#Floating-Point-Concepts" title="Floating Point Concepts"> |
| <link rel="next" href="IEEE-Floating-Point.html#IEEE-Floating-Point" title="IEEE Floating Point"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Floating-Point-Parameters"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="IEEE-Floating-Point.html#IEEE-Floating-Point">IEEE Floating Point</a>, |
| Previous: <a rel="previous" accesskey="p" href="Floating-Point-Concepts.html#Floating-Point-Concepts">Floating Point Concepts</a>, |
| Up: <a rel="up" accesskey="u" href="Floating-Type-Macros.html#Floating-Type-Macros">Floating Type Macros</a> |
| <hr> |
| </div> |
| |
| <h5 class="subsubsection">A.5.3.2 Floating Point Parameters</h5> |
| |
| <p><a name="index-float_002eh-3780"></a>These macro definitions can be accessed by including the header file |
| <samp><span class="file">float.h</span></samp> in your program. |
| |
| <p>Macro names starting with ‘<samp><span class="samp">FLT_</span></samp>’ refer to the <code>float</code> type, |
| while names beginning with ‘<samp><span class="samp">DBL_</span></samp>’ refer to the <code>double</code> type |
| and names beginning with ‘<samp><span class="samp">LDBL_</span></samp>’ refer to the <code>long double</code> |
| type. (If GCC does not support <code>long double</code> as a distinct data |
| type on a target machine then the values for the ‘<samp><span class="samp">LDBL_</span></samp>’ constants |
| are equal to the corresponding constants for the <code>double</code> type.) |
| |
| <p>Of these macros, only <code>FLT_RADIX</code> is guaranteed to be a constant |
| expression. The other macros listed here cannot be reliably used in |
| places that require constant expressions, such as ‘<samp><span class="samp">#if</span></samp>’ |
| preprocessing directives or in the dimensions of static arrays. |
| |
| <p>Although the ISO C<!-- /@w --> standard specifies minimum and maximum values for |
| most of these parameters, the GNU C implementation uses whatever values |
| describe the floating point representation of the target machine. So in |
| principle GNU C actually satisfies the ISO C<!-- /@w --> requirements only if the |
| target machine is suitable. In practice, all the machines currently |
| supported are suitable. |
| |
| <dl> |
| <!-- float.h --> |
| <!-- ISO --> |
| <dt><code>FLT_ROUNDS</code><a name="index-FLT_005fROUNDS-3781"></a><dd>This value characterizes the rounding mode for floating point addition. |
| The following values indicate standard rounding modes: |
| |
| <dl> |
| <dt><code>-1</code><dd>The mode is indeterminable. |
| <br><dt><code>0</code><dd>Rounding is towards zero. |
| <br><dt><code>1</code><dd>Rounding is to the nearest number. |
| <br><dt><code>2</code><dd>Rounding is towards positive infinity. |
| <br><dt><code>3</code><dd>Rounding is towards negative infinity. |
| </dl> |
| |
| <p class="noindent">Any other value represents a machine-dependent nonstandard rounding |
| mode. |
| |
| <p>On most machines, the value is <code>1</code>, in accordance with the IEEE |
| standard for floating point. |
| |
| <p>Here is a table showing how certain values round for each possible value |
| of <code>FLT_ROUNDS</code>, if the other aspects of the representation match |
| the IEEE single-precision standard. |
| |
| <pre class="smallexample"> 0 1 2 3 |
| 1.00000003 1.0 1.0 1.00000012 1.0 |
| 1.00000007 1.0 1.00000012 1.00000012 1.0 |
| -1.00000003 -1.0 -1.0 -1.0 -1.00000012 |
| -1.00000007 -1.0 -1.00000012 -1.0 -1.00000012 |
| </pre> |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_RADIX</code><a name="index-FLT_005fRADIX-3782"></a><dd>This is the value of the base, or radix, of the exponent representation. |
| This is guaranteed to be a constant expression, unlike the other macros |
| described in this section. The value is 2 on all machines we know of |
| except the IBM 360 and derivatives. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MANT_DIG</code><a name="index-FLT_005fMANT_005fDIG-3783"></a><dd>This is the number of base-<code>FLT_RADIX</code> digits in the floating point |
| mantissa for the <code>float</code> data type. The following expression |
| yields <code>1.0</code> (even though mathematically it should not) due to the |
| limited number of mantissa digits: |
| |
| <pre class="smallexample"> float radix = FLT_RADIX; |
| |
| 1.0f + 1.0f / radix / radix / ... / radix |
| </pre> |
| <p class="noindent">where <code>radix</code> appears <code>FLT_MANT_DIG</code> times. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MANT_DIG</code><a name="index-DBL_005fMANT_005fDIG-3784"></a><dt><code>LDBL_MANT_DIG</code><a name="index-LDBL_005fMANT_005fDIG-3785"></a><dd>This is the number of base-<code>FLT_RADIX</code> digits in the floating point |
| mantissa for the data types <code>double</code> and <code>long double</code>, |
| respectively. |
| |
| <!-- Extra blank lines make it look better. --> |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_DIG</code><a name="index-FLT_005fDIG-3786"></a><dd> |
| This is the number of decimal digits of precision for the <code>float</code> |
| data type. Technically, if <var>p</var> and <var>b</var> are the precision and |
| base (respectively) for the representation, then the decimal precision |
| <var>q</var> is the maximum number of decimal digits such that any floating |
| point number with <var>q</var> base 10 digits can be rounded to a floating |
| point number with <var>p</var> base <var>b</var> digits and back again, without |
| change to the <var>q</var> decimal digits. |
| |
| <p>The value of this macro is supposed to be at least <code>6</code>, to satisfy |
| ISO C<!-- /@w -->. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_DIG</code><a name="index-DBL_005fDIG-3787"></a><dt><code>LDBL_DIG</code><a name="index-LDBL_005fDIG-3788"></a><dd> |
| These are similar to <code>FLT_DIG</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. The values of these |
| macros are supposed to be at least <code>10</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MIN_EXP</code><a name="index-FLT_005fMIN_005fEXP-3789"></a><dd>This is the smallest possible exponent value for type <code>float</code>. |
| More precisely, is the minimum negative integer such that the value |
| <code>FLT_RADIX</code> raised to this power minus 1 can be represented as a |
| normalized floating point number of type <code>float</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MIN_EXP</code><a name="index-DBL_005fMIN_005fEXP-3790"></a><dt><code>LDBL_MIN_EXP</code><a name="index-LDBL_005fMIN_005fEXP-3791"></a><dd> |
| These are similar to <code>FLT_MIN_EXP</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MIN_10_EXP</code><a name="index-FLT_005fMIN_005f10_005fEXP-3792"></a><dd>This is the minimum negative integer such that <code>10</code> raised to this |
| power minus 1 can be represented as a normalized floating point number |
| of type <code>float</code>. This is supposed to be <code>-37</code> or even less. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MIN_10_EXP</code><a name="index-DBL_005fMIN_005f10_005fEXP-3793"></a><dt><code>LDBL_MIN_10_EXP</code><a name="index-LDBL_005fMIN_005f10_005fEXP-3794"></a><dd>These are similar to <code>FLT_MIN_10_EXP</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MAX_EXP</code><a name="index-FLT_005fMAX_005fEXP-3795"></a><dd>This is the largest possible exponent value for type <code>float</code>. More |
| precisely, this is the maximum positive integer such that value |
| <code>FLT_RADIX</code> raised to this power minus 1 can be represented as a |
| floating point number of type <code>float</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MAX_EXP</code><a name="index-DBL_005fMAX_005fEXP-3796"></a><dt><code>LDBL_MAX_EXP</code><a name="index-LDBL_005fMAX_005fEXP-3797"></a><dd>These are similar to <code>FLT_MAX_EXP</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MAX_10_EXP</code><a name="index-FLT_005fMAX_005f10_005fEXP-3798"></a><dd>This is the maximum positive integer such that <code>10</code> raised to this |
| power minus 1 can be represented as a normalized floating point number |
| of type <code>float</code>. This is supposed to be at least <code>37</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MAX_10_EXP</code><a name="index-DBL_005fMAX_005f10_005fEXP-3799"></a><dt><code>LDBL_MAX_10_EXP</code><a name="index-LDBL_005fMAX_005f10_005fEXP-3800"></a><dd>These are similar to <code>FLT_MAX_10_EXP</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MAX</code><a name="index-FLT_005fMAX-3801"></a><dd> |
| The value of this macro is the maximum number representable in type |
| <code>float</code>. It is supposed to be at least <code>1E+37</code>. The value |
| has type <code>float</code>. |
| |
| <p>The smallest representable number is <code>- FLT_MAX</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MAX</code><a name="index-DBL_005fMAX-3802"></a><dt><code>LDBL_MAX</code><a name="index-LDBL_005fMAX-3803"></a><dd> |
| These are similar to <code>FLT_MAX</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. The type of the |
| macro's value is the same as the type it describes. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_MIN</code><a name="index-FLT_005fMIN-3804"></a><dd> |
| The value of this macro is the minimum normalized positive floating |
| point number that is representable in type <code>float</code>. It is supposed |
| to be no more than <code>1E-37</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_MIN</code><a name="index-DBL_005fMIN-3805"></a><dt><code>LDBL_MIN</code><a name="index-LDBL_005fMIN-3806"></a><dd> |
| These are similar to <code>FLT_MIN</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. The type of the |
| macro's value is the same as the type it describes. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>FLT_EPSILON</code><a name="index-FLT_005fEPSILON-3807"></a><dd> |
| This is the minimum positive floating point number of type <code>float</code> |
| such that <code>1.0 + FLT_EPSILON != 1.0</code> is true. It's supposed to |
| be no greater than <code>1E-5</code>. |
| |
| <!-- float.h --> |
| <!-- ISO --> |
| <br><dt><code>DBL_EPSILON</code><a name="index-DBL_005fEPSILON-3808"></a><dt><code>LDBL_EPSILON</code><a name="index-LDBL_005fEPSILON-3809"></a><dd> |
| These are similar to <code>FLT_EPSILON</code>, but for the data types |
| <code>double</code> and <code>long double</code>, respectively. The type of the |
| macro's value is the same as the type it describes. The values are not |
| supposed to be greater than <code>1E-9</code>. |
| </dl> |
| |
| </body></html> |
| |
