(split) Apply minor changes from v3.32 to v3.35 in the upstream.

[linuxjm/LDP_man-pages.git] / draft / man7 / math_error.7

.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Japanese Version Copyright (c) 2008  Akihiro MOTOKI
.\"         all rights reserved.
.\" Translated 2008-08-17, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v3.07
.\" 
.\"WORD:        significand     ²¾¿ôÉô
.\"WORD:        domain error    Îΰ襨¥é¡¼
.\"WORD:        pole error      ¶Ë¥¨¥é¡¼
.\"WORD:        range error     ÈÏ°Ï¥¨¥é¡¼
.\" 
.TH MATH_ERROR 7 2008-08-11 "Linux" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O math_error \- detecting errors from mathematical functions
math_error \- ¿ô³Ø´Ø¿ô¤«¤é¤Î¥¨¥é¡¼¤Î¸¡½Ð
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.nf
.B #include <math.h>
.B #include <errno.h>
.B #include <fenv.h>
.fi
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O When an error occurs,
.\"O most library functions indicate this fact by returning a special value
.\"O (e.g., \-1 or NULL).
.\"O Because they typically return a floating-point number,
.\"O the mathematical functions declared in
.\"O .IR <math.h>
.\"O indicate an error using other mechanisms.
.\"O There are two error-reporting mechanisms:
.\"O the older one sets
.\"O .IR errno ;
.\"O the newer one uses the floating-point exception mechanism (the use of
.\"O .BR feclearexcept (3)
.\"O and
.\"O .BR fetestexcept (3),
.\"O as outlined below)
.\"O described in
.\"O .BR fenv (3).
¥¨¥é¡¼¤¬È¯À¸¤¹¤ë¤È¡¢¤Û¤È¤ó¤É¤Î¥é¥¤¥Ö¥é¥ê´Ø¿ô¤Ï (\-1 ¤ä NULL ¤Ê¤É¤Î)
ÆÃÊ̤ÊÃͤòÊÖ¤¹¤³¤È¤Ç¥¨¥é¡¼¤òÄÌÃΤ¹¤ë¡£
.I <math.h>
¤ÇÀë¸À¤µ¤ì¤Æ¤¤¤ë¿ô³Ø´Ø¿ô¤Ï¡¢Ä̾ï¤ÏÉâÆ°¾®¿ôÅÀÃͤòÊÖ¤¹¤Î¤Ç¡¢
¾¤Îµ¡¹½¤ò»È¤Ã¤Æ¥¨¥é¡¼¤òÄÌÃΤ¹¤ë¡£
¥¨¥é¡¼ÄÌÃε¡¹½¤Ï 2 ¼ïÎढ¤ê¡¢
¸Å¤¤¤â¤Î¤¬
.I errno
¤òÀßÄꤹ¤ë¤ä¤êÊý¤Ç¤¢¤ê¡¢¿·¤·¤¤¤â¤Î¤¬
.BR fenv (3)
¤ÇÀâÌÀ¤µ¤ì¤Æ¤¤¤ëÉâÆ°¾®¿ôÅÀÎã³°µ¡¹½¤Ç¤¢¤ë¡£
.RB ( feclearexcept (3)
¤È
.BR fetestexcept (3)
¤ò»ÈÍѤ¹¤ë¡£¤³¤ì¤é¤Ë¤Ä¤¤¤Æ¤Ï°Ê²¼¤Ç³µÍפòÀâÌÀ¤·¤Æ¤¤¤ë¡£)

.\"O A portable program that needs to check for an error from a mathematical
.\"O function should set
.\"O .I errno
.\"O to zero, and make the following call
°Ü¿¢À­¤¬É¬Í×¤Ê¥×¥í¥°¥é¥à¤Ç¡¢¿ô³Ø´Ø¿ô¤«¤é¤Î¥¨¥é¡¼¤ò³Îǧ¤¹¤ëɬÍפ¬¤¢¤ë¾ì¹ç¤Ë¤Ï¡¢
¿ô³Ø´Ø¿ô¤ò¸Æ¤Ó½Ð¤¹Á°¤Ë
.I errno
¤ò 0 ¤ËÀßÄꤷ¡¢°Ê²¼¤ò¸Æ¤Ó½Ð¤¹¤Ù¤­¤Ç¤¢¤ë¡£
.in +4n
.nf

feclearexcept(FE_ALL_EXCEPT);
.\"O 
.fi
.in
.\"O before calling a mathematical function.
.\"Omotoki: Âбþ¤¹¤ëÌõ¤Ï feclearexcept ¤Î°úÍѤÎÁ°¤Ë¤¢¤ë¡£

.\"O Upon return from the mathematical function, if
.\"O .I errno
.\"O is nonzero, or the following call (see
.\"O .BR fenv (3))
.\"O returns nonzero
¿ô³Ø´Ø¿ô¤«¤éÊ֤äƤ­¤¿ºÝ¤Ë¡¢
.I errno
¤¬ 0 °Ê³°¤«¡¢°Ê²¼¤Î¸Æ¤Ó½Ð¤·¤¬ 0 °Ê³°¤òÊÖ¤·¤¿¾ì¹ç
.RB ( fenv (3)
»²¾È)¡¢¿ô³Ø´Ø¿ô¤Ç¥¨¥é¡¼¤¬È¯À¸¤·¤Æ¤¤¤ë¡£
.in +4n
.nf

fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
             FE_UNDERFLOW);
.\"O 
.fi
.in
.\" enum
.\" {
.\" FE_INVALID = 0x01,
.\" __FE_DENORM = 0x02,
.\" FE_DIVBYZERO = 0x04,
.\" FE_OVERFLOW = 0x08,
.\" FE_UNDERFLOW = 0x10,
.\" FE_INEXACT = 0x20
.\" };
.\"O then an error occurred in the mathematical function.
.\"Omotoki: Âбþ¤¹¤ëÌõ¤Ï fetestexcept ¤Î°úÍѤÎÁ°¤Ë¤¢¤ë¡£

.\"O The error conditions that can occur for mathematical functions
.\"O are described below.
¿ô³Ø´Ø¿ô¤ÇȯÀ¸¤¹¤ë¥¨¥é¡¼¾ò·ï¤Ë¤Ä¤¤¤Æ¤Ï°Ê²¼¤ÇÀâÌÀ¤¹¤ë¡£
.\"O .SS Domain Error
.SS Îΰ襨¥é¡¼ (domain error)
.\"O A
.\"O .I domain error
.\"O occurs when a mathematical function is supplied with an argument whose
.\"O value falls outside the domain for which the function
.\"O is defined (e.g., giving a negative argument to
.\"O .BR log (3)).
.\"O When a domain error occurs,
.\"O math functions commonly return a NaN
.\"O (though some functions return a different value in this case);
.\"O .I errno
.\"O is set to
.\"O .BR EDOM ,
.\"O and an "invalid"
.\"O .RB ( FE_INVALID )
.\"O floating-point exception is raised.
.I Îΰ襨¥é¡¼
¤¬È¯À¸¤¹¤ë¤Î¤Ï¡¢¿ô³Ø´Ø¿ô¤ËÅϤµ¤ì¤¿°ú¤­¿ô¤ÎÃͤ¬¤½¤Î´Ø¿ô¤¬ÄêµÁ¤µ¤ì¤Æ¤¤¤ë
Îΰè¤ËÆþ¤Ã¤Æ¤¤¤Ê¤¤¾ì¹ç¤Ç¤¢¤ë (Î㤨¤Ð
.BR log (3)
¤ËÉé¤Î°ú¤­¿ô¤òÅϤ·¤¿¾ì¹ç)¡£
Îΰ襨¥é¡¼¤¬È¯À¸¤¹¤ë¤È¡¢
¿ô³Ø´Ø¿ô¤ÏÉáÄÌ¤Ï NaN ¤òÊÖ¤·
(Ʊ¤¸¾õ¶·¤Ç°ã¤¦ÃͤòÊÖ¤¹´Ø¿ô¤â¤¢¤ë)¡¢
.I errno
¤Ë
.B EDOM
¤òÀßÄꤷ¡¢¡Ö̵¸ú (invalid)¡×
ÉâÆ°¾®¿ôÅÀÎã³°
.RB ( FE_INVALID )
¤ò¾å¤²¤ë¡£
.\"O .SS Pole Error
.SS ¶Ë¥¨¥é¡¼ (pole error)
.\"O A
.\"O .I pole error
.\"O occurs when the mathematical result of a function is an exact infinity
.\"O (e.g., the logarithm of 0 is negative infinity).
.\"O When a pole error occurs,
.\"O the function returns the (signed) value
.\"O .BR HUGE_VAL ,
.\"O .BR HUGE_VALF ,
.\"O or
.\"O .BR HUGE_VALL ,
.\"O depending on whether the function result type is
.\"O .IR double ,
.\"O .IR float ,
.\"O or
.\"O .IR "long double" .
.\"O The sign of the result is that which is mathematically correct for
.\"O the function.
.I ¶Ë¥¨¥é¡¼
¤¬È¯À¸¤¹¤ë¤Î¤Ï¡¢´Ø¿ô¤Î¿ô³ØŪ¤Ê·ë²Ì¤¬Ìµ¸ÂÂ礽¤Î¤â¤Î¤È¤Ê¤ë¾ì¹ç¤Ç¤¢¤ë
(Î㤨¤Ð
0 ¤ÎÂпô¤ÏÉé¤Î̵¸ÂÂç¤Ç¤¢¤ë)¡£
¶Ë¥¨¥é¡¼¤¬È¯À¸¤¹¤ë¤È¡¢¤½¤Î´Ø¿ô¤ÎÊÖ¤êÃÍ¤Ï (Éä¹æÉÕ¤­¤Î)
.BR HUGE_VAL ,
.BR HUGE_VALF ,
.B HUGE_VALL
¤Î¤¤¤º¤ì¤«¤È¤Ê¤ë (Á°µ­¤ÎÃͤΤ¦¤Á¤É¤ì¤¬Ê֤뤫¤Ï´Ø¿ô¤ÎÊÖ¤êÃͤη¿¤Ë¤è¤ê·è¤Þ¤ê¡¢
¤½¤ì¤¾¤ì
.IR double ,
.IR float ,
.I "long double"
¤ËÂбþ¤¹¤ë)¡£
·ë²Ì¤ÎÉä¹æ¤Ï¡¢¤½¤Î´Ø¿ô¤Î¿ô³ØŪ¤ÊÄêµÁ¤«¤é·èÄꤵ¤ì¤ë¡£
.\"O .I errno
.\"O is set to
.\"O .BR ERANGE ,
.\"O and a "divide-by-zero"
.\"O .RB ( FE_DIVBYZERO )
.\"O floating-point exception is raised.
.I errno
¤Ï
.B ERANGE
¤ËÀßÄꤵ¤ì¡¢¡Ö0 ¤Ë¤è¤ë½ü»» (divide-by-zero)¡×
ÉâÆ°¾®¿ôÅÀÎã³°
.RB ( FE_DIVBYZERO )
¤¬¾å¤¬¤ë¡£
.\"O .SS Range Error
.SS ÈÏ°Ï¥¨¥é¡¼ (range ¥¨¥é¡¼)
.\"O A
.\"O .I range error
.\"O occurs when the magnitude of the function result means that it
.\"O cannot be represented in the result type of the function.
.\"O The return value of the function depends on whether the range error
.\"O was an overflow or an underflow.
.I ÈÏ°Ï¥¨¥é¡¼
¤¬È¯À¸¤¹¤ë¤Î¤Ï¡¢´Ø¿ô¤Î·ë²Ì¤ÎÃͤ¬¤½¤Î´Ø¿ô¤ÎÊÖ¤êÃͤη¿¤Ç¤Ïɽ¸½¤Ç¤­¤Ê¤¤¾ì¹ç
¤Ç¤¢¤ë¡£´Ø¿ô¤ÎÊÖ¤êÃͤϡ¢ÈÏ°Ï¥¨¥é¡¼¤¬¥ª¡¼¥Ð¡¼¥Õ¥í¡¼¤Ç¤¢¤Ã¤¿¤«¥¢¥ó¥À¡¼¥Õ¥í¡¼
¤Ç¤¢¤Ã¤¿¤«¤Ë¤è¤Ã¤Æ°Û¤Ê¤ë¡£

.\"O A floating result
.\"O .I overflows
.\"O if the result is finite,
.\"O but is too large to represented in the result type.
.\"O When an overflow occurs,
.\"O the function returns the value
.\"O .BR HUGE_VAL ,
.\"O .BR HUGE_VALF ,
.\"O or
.\"O .BR HUGE_VALL ,
.\"O depending on whether the function result type is
.\"O .IR double ,
.\"O .IR float ,
.\"O or
.\"O .IR "long double" .
.\"O .I errno
.\"O is set to
.\"O .BR ERANGE ,
.\"O and an "overflow"
.\"O .RB ( FE_OVERFLOW )
.\"O floating-point exception is raised.
ÉâÆ°¾®¿ôÅÀ¤Î¥ª¡¼¥Ð¡¼¥Õ¥í¡¼¤Ï¡¢·ë²Ì¤¬Í­¸Â¤À¤¬¡¢Â礭²á¤®¤Æ
·ë²Ì¤òÊÖ¤¹·¿¤Ç¤Ïɽ¸½¤Ç¤­¤Ê¤¤¾ì¹ç¤ËȯÀ¸¤¹¤ë¡£
¥ª¡¼¥Ð¡¼¥Õ¥í¡¼¤¬È¯À¸¤¹¤ë¤È¡¢
¤½¤Î´Ø¿ô¤Ï
.BR HUGE_VAL ,
.BR HUGE_VALF ,
.B HUGE_VALL
¤Î¤¤¤º¤ì¤«¤òÊÖ¤¹ (Á°µ­¤ÎÃͤΤ¦¤Á¤É¤ì¤¬Ê֤뤫¤Ï´Ø¿ô¤ÎÊÖ¤êÃͤη¿¤Ë¤è¤ê·è¤Þ¤ê¡¢
¤½¤ì¤¾¤ì
.IR double ,
.IR float ,
.I "long double"
¤ËÂбþ¤¹¤ë)¡£
.I errno
¤Ï
.B ERANGE
¤ËÀßÄꤵ¤ì¡¢¡Ö¥ª¡¼¥Ð¡¼¥Õ¥í¡¼ (overflow)¡×
ÉâÆ°¾®¿ôÅÀÎã³°
.RB ( FE_OVERFLOW )
¤¬¾å¤¬¤ë¡£

.\"O A floating result
.\"O .I underflows
.\"O if the result is too small to be represented in the result type.
.\"O If an underflow occurs,
.\"O a mathematical function typically returns 0.0
.\"O (C99 says a function shall return "an implementation-defined value
.\"O whose magnitude is no greater than the smallest normalized
.\"O positive number in the specified type").
ÉâÆ°¾®¿ôÅÀ¤Î¥¢¥ó¥À¡¼¥Õ¥í¡¼¤Ï¡¢
·ë²Ì¤¬¾®¤µ²á¤®¤Æ¡¢·ë²Ì¤òÊÖ¤¹·¿¤Ç¤Ïɽ¸½¤Ç¤­¤Ê¤¤¾ì¹ç¤ËȯÀ¸¤¹¤ë¡£
¥¢¥ó¥À¡¼¥Õ¥í¡¼¤¬È¯À¸¤¹¤ë¤È¡¢¿ô³Ø´Ø¿ô¤ÏÄ̾ï¤Ï 0.0 ¤òÊÖ¤¹
(C99 ¤Ç¤Ï¡¢»ØÄꤵ¤ì¤¿·¿¤Ë¤ª¤¤¤ÆºÇ¾®¤ÎÀµµ¬²½¤µ¤ì¤¿Àµ¤ÎÃͤè¤êÂ礭¤¯¤Ê¤¤
Ãͤò»ý¤Ä¼ÂÁõÄêµÁ (implementation-defined) ¤ÎÃͤòÊÖ¤¹¡¢¤È¤Ê¤Ã¤Æ¤¤¤ë)¡£
.\"O .I errno
.\"O may be set to
.\"O .BR ERANGE ,
.\"O and an "overflow"
.\"O .RB ( FE_UNDERFLOW )
.\"O floating-point exception may be raised.
.I errno
¤Ï
.B ERANGE
¤ËÀßÄꤵ¤ì¡¢¡Ö¥¢¥ó¥À¡¼¥Õ¥í¡¼¡×ÉâÆ°¾®¿ôÅÀÎã³°
.RB ( FE_UNDERFLOW )
¤¬¾å¤¬¤ë¡£

.\"O Some functions deliver a range error if the supplied argument value,
.\"O or the correct function result, would be
.\"O .IR subnormal .
.\"O A subnormal value is one that is nonzero,
.\"O but with a magnitude that is so small that
.\"O it can't be presented in normalized form
.\"O (i.e., with a 1 in the most significant bit of the significand).
.\"O The representation of a subnormal number will contain one
.\"O or more leading zeros in the significand.
¤¤¤¯¤Ä¤«¤Î´Ø¿ô¤Ç¤Ï¡¢ÅϤµ¤ì¤¿°ú¤­¿ô¤ÎÃͤ䡢Àµ¤·¤¤´Ø¿ô¤Î·ë²Ì¤¬
.I subnormal (ÈóÀµµ¬²½¿ô)
¤Ë¤Ê¤ë¾ì¹ç¤ËÈÏ°Ï¥¨¥é¡¼¤ò¾å¤²¤ë¡£
subnormal ¤ÊÃͤȤϡ¢0 ¤Ç¤Ï¤Ê¤¤¤¬¡¢¤½¤ÎÃͤ¬¾®¤µ¤¹¤®¤Æ
(²¾¿ôÉô¤ÎºÇ¾å°Ì¥Ó¥Ã¥È¤¬ 1 ¤È¤Ê¤ë) ɸ½à·Á¤Ç¤Ïɽ¸½¤Ç¤­¤Ê¤¤¤è¤¦¤ÊÃͤǤ¢¤ë¡£
subnormal ¤ÊÃͤÎɽ¸½¤Ç¤Ï¡¢²¾¿ôÉô¤Î¾å°Ì¦¤Î¥Ó¥Ã¥È¤Ë 1 ¸Ä°Ê¾å¤Î 0 ¤¬
´Þ¤Þ¤ì¤ë¤³¤È¤Ë¤Ê¤ë¡£
.\"O .SH NOTES
.SH Ãí°Õ
.\"O The
.\"O .I math_errhandling
.\"O identifier specified by C99 and POSIX.1-2001 is not supported by glibc.
C99 ¤È POSIX.1-2001 ¤Çµ¬Äꤵ¤ì¤Æ¤¤¤ë
.I math_errhandling
¼±ÊÌ»Ò¤Ï glibc ¤Ç¤Ï¥µ¥Ý¡¼¥È¤µ¤ì¤Æ¤¤¤Ê¤¤¡£
.\" See CONFORMANCE in the glibc 2.8 (and earlier) source.
.\"O This identifier is supposed to indicate which of the two
.\"O error-notification mechanisms
.\"O .RI ( errno ,
.\"O exceptions retrievable via
.\"O .BR fettestexcept (3))
.\"O is in use.
¤³¤Î¼±Ê̻Ҥϡ¢2 ¤Ä¤Î¥¨¥é¡¼ÄÌÃε¡¹½
.RI ( errno
¤È
.BR fetestexcept (3)
·Ðͳ¤Ç¼èÆÀ¤Ç¤­¤ëÎã³°) ¤Î¤¦¤Á¤É¤Á¤é¤¬»ÈÍѤµ¤ì¤Æ¤¤¤ë¤«¤òÄÌÃÎ
¤¹¤ë¤³¤È¤Ë¤Ê¤Ã¤Æ¤¤¤ë¡£
.\"O The standards require that at least one be in use,
.\"O but permit both to be available.
.\"O The current (version 2.8) situation under glibc is messy.
.\"O Most (but not all) functions raise exceptions on errors.
.\"O Some also set
.\"O .IR errno .
.\"O A few functions set
.\"O .IR errno ,
.\"O but don't raise an exception.
.\"O A very few functions do neither.
.\"O See the individual manual pages for details.
ɸ½à¤Ç¤Ï¡¢¾¯¤Ê¤¯¤È¤â°ì¤Ä¤Ï»ÈÍѤµ¤ì¤ë¤³¤È¤¬Í׵ᤵ¤ì¤Æ¤¤¤ë¤¬¡¢
ξÊý¤È¤âÍøÍѲÄǽ¤Ç¤¢¤Ã¤Æ¤â¤è¤¤¤È¤µ¤ì¤Æ¤¤¤ë¡£
glibc ¤Ç¤Î¸½ºß¤Î (¥Ð¡¼¥¸¥ç¥ó 2.8 ¤Ç¤Î) ¾õ¶·¤Ï¤«¤Ê¤êº®Í𤷤Ƥ¤¤ë¡£
¤Û¤È¤ó¤É¤Î´Ø¿ô (¤¿¤À¤·Á´Éô¤Ç¤Ï¤Ê¤¤) ¤Ï¥¨¥é¡¼»þ¤ËÎã³°¤ò¾å¤²¤ë¡£
¤¤¤¯¤Ä¤«¤Î´Ø¿ô¤Ï
.I errno
¤âÀßÄꤹ¤ë¡£
.I errno
¤òÀßÄꤹ¤ë¤¬¡¢Îã³°¤ò¾å¤²¤Ê¤¤´Ø¿ô¤â¾¯¤·¤À¤±Â¸ºß¤¹¤ë¡£
¤É¤Á¤é¤â¹Ô¤ï¤Ê¤¤´Ø¿ô¤â¤´¤¯¾¯¿ô¤À¤¬Â¸ºß¤¹¤ë¡£
¾ÜºÙ¤Ë¤Ä¤¤¤Æ¤Ï¸Ä¡¹¤Î¥Þ¥Ë¥å¥¢¥ë¥Ú¡¼¥¸¤ò»²¾È¤Î¤³¤È¡£

.\"O To avoid the complexities of using
.\"O .I errno
.\"O and
.\"O .BR fetestexcept (3)
.\"O for error checking,
.\"O it is often advised that one should instead check for bad argument
.\"O values before each call.
.I errno
¤È
.BR fetestexcept (3)
¤ÎξÊý¤ò»È¤Ã¤Æ¥¨¥é¡¼¥Á¥§¥Ã¥¯¤ò¹Ô¤¦¤³¤È¤ÇÊ£»¨¤Ë¤Ê¤ë¤Î¤òÈò¤±¤ë¤¿¤á¡¢
¿¤¯¤Î¾ì¹ç¡¢´Ø¿ô¸Æ¤Ó½Ð¤·¤ò¹Ô¤¦Á°¤ËÉÔÀµ¤Ê°ú¤­¿ô¤«¤Î¥Á¥§¥Ã¥¯¤ò¹Ô¤¦
ÊýË¡¤¬¿ä¾©¤µ¤ì¤Æ¤¤¤ë¡£
.\" http://www.securecoding.cert.org/confluence/display/seccode/FLP32-C.+Prevent+or+detect+domain+and+range+errors+in+math+functions
.\"O For example, the following code ensures that
.\"O .BR log (3)'s
.\"O argument is not a NaN and is not zero (a pole error) or
.\"O less than zero (a domain error):
Î㤨¤Ð¡¢°Ê²¼¤Î¥³¡¼¥É¤Ï¡¢
.BR log (3)
¤Î°ú¤­¿ô¤¬ NaN ¤Ç¤â (¶Ë¥¨¥é¡¼¤È¤Ê¤ë) 0 ¤Ç¤â (Îΰ襨¥é¡¼¤È¤Ê¤ë) 0 ̤Ëþ
¤Ç¤â¤Ê¤¤¤³¤È¤òÊݾڤ¹¤ë¤â¤Î¤Ç¤¢¤ë¡£
.in +4n
.nf

double x, r;

if (isnan(x) || islessequal(x, 0)) {
    /* Deal with NaN / pole error / domain error */
}

r = log(x);

.fi
.in
.\"O The discussion on this page does not apply to the complex
.\"O mathematical functions (i.e., those declared by
.\"O .IR <complex.h> ),
.\"O which in general are not required to return errors by C99
.\"O and POSIX.1-2001.
¤³¤Î¥Ú¡¼¥¸¤Ë½ñ¤«¤ì¤Æ¤¤¤ë¤³¤È¤Ï¡¢
.RI ( <complex.h>
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°ìÈ̤ˡ¢C99 ¤ä POSIX.1-2001 ¤Ç¤Ï¤³¤ì¤é¤Î´Ø¿ô¤¬¥¨¥é¡¼¤òÊÖ¤¹¤³¤È¤ò
Í׵ᤷ¤Æ¤Ê¤¤¡£

.\"O The
.\"O .BR gcc (1)
.\"O .I "-fno-math-errno"
.\"O option causes the executable to employ implementations of some
.\"O mathematical functions that are faster than the standard
.\"O implementations, but do not set
.\"O .I errno
.\"O on error.
.\"O (The
.\"O .BR gcc (1)
.\"O .I "-ffast-math"
.\"O option also enables
.\"O .IR "-fno-math-errno" .)
.\"O An error can still be tested for using
.\"O .BR fetestexcept (3).
.BR gcc (1)
¤Î
.I "-fno-math-errno"
¥ª¥×¥·¥ç¥ó¤ò»È¤¦¤È¡¢¼Â¹Ô¥Õ¥¡¥¤¥ë¤Ç¡¢É¸½à¤Î¼ÂÁõ¤è¤ê¤â¹â®¤Ê¿ô³Ø´Ø¿ô¤Î
¼ÂÁõ¤¬»ÈÍѤµ¤ì¤ë¤è¤¦¤Ë¤Ê¤ë¤¬¡¢
¥¨¥é¡¼»þ¤Ë
.I errno
¤¬ÀßÄꤵ¤ì¤Ê¤¤
.RB ( gcc (1)
¤Î
.I "-ffast-math"
¥ª¥×¥·¥ç¥ó¤ò»ØÄꤷ¤¿¾ì¹ç¤Ë¤â
.I "-fno-math-errno"
¤ÏÍ­¸ú¤Ë¤Ê¤ë)¡£
¤³¤Î¥ª¥×¥·¥ç¥ó¤ò»ØÄꤷ¤¿¾ì¹ç¤Ç¤â¡¢
.BR fetestexcept (3)
¤ò»È¤Ã¤¿¥¨¥é¡¼¤Î¸¡ºº¤Ï²Äǽ¤Ç¤¢¤ë¡£
.\"O .SH SEE ALSO
.SH ´ØÏ¢¹àÌÜ
.BR gcc (1),
.BR errno (3),
.BR fenv (3),
.BR fpclassify (3),
.BR INFINITY (3),
.BR isgreater (3),
.BR matherr (3),
.BR nan (3)
.br
.I "info libc"