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-.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
-.\" <mtk.manpages@gmail.com>
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.TH math_error 7 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-math_error \- detecting errors from mathematical functions
-.SH SYNOPSIS
-.nf
-.B #include <math.h>
-.B #include <errno.h>
-.B #include <fenv.h>
-.fi
-.SH DESCRIPTION
-When an error occurs,
-most library functions indicate this fact by returning a special value
-(e.g., \-1 or NULL).
-Because they typically return a floating-point number,
-the mathematical functions declared in
-.I <math.h>
-indicate an error using other mechanisms.
-There are two error-reporting mechanisms:
-the older one sets
-.IR errno ;
-the newer one uses the floating-point exception mechanism (the use of
-.BR feclearexcept (3)
-and
-.BR fetestexcept (3),
-as outlined below)
-described in
-.BR fenv (3).
-.P
-A portable program that needs to check for an error from a mathematical
-function should set
-.I errno
-to zero, and make the following call
-.P
-.in +4n
-.EX
-feclearexcept(FE_ALL_EXCEPT);
-.EE
-.in
-.P
-before calling a mathematical function.
-.P
-Upon return from the mathematical function, if
-.I errno
-is nonzero, or the following call (see
-.BR fenv (3))
-returns nonzero
-.P
-.in +4n
-.EX
-fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
- FE_UNDERFLOW);
-.EE
-.in
-.P
-.\" enum
-.\" {
-.\" FE_INVALID = 0x01,
-.\" __FE_DENORM = 0x02,
-.\" FE_DIVBYZERO = 0x04,
-.\" FE_OVERFLOW = 0x08,
-.\" FE_UNDERFLOW = 0x10,
-.\" FE_INEXACT = 0x20
-.\" };
-then an error occurred in the mathematical function.
-.P
-The error conditions that can occur for mathematical functions
-are described below.
-.SS Domain error
-A
-.I domain error
-occurs when a mathematical function is supplied with an argument whose
-value falls outside the domain for which the function
-is defined (e.g., giving a negative argument to
-.BR log (3)).
-When a domain error occurs,
-math functions commonly return a NaN
-(though some functions return a different value in this case);
-.I errno
-is set to
-.BR EDOM ,
-and an "invalid"
-.RB ( FE_INVALID )
-floating-point exception is raised.
-.SS Pole error
-A
-.I pole error
-occurs when the mathematical result of a function is an exact infinity
-(e.g., the logarithm of 0 is negative infinity).
-When a pole error occurs,
-the function returns the (signed) value
-.BR HUGE_VAL ,
-.BR HUGE_VALF ,
-or
-.BR HUGE_VALL ,
-depending on whether the function result type is
-.IR double ,
-.IR float ,
-or
-.IR "long double" .
-The sign of the result is that which is mathematically correct for
-the function.
-.I errno
-is set to
-.BR ERANGE ,
-and a "divide-by-zero"
-.RB ( FE_DIVBYZERO )
-floating-point exception is raised.
-.SS Range error
-A
-.I range error
-occurs when the magnitude of the function result means that it
-cannot be represented in the result type of the function.
-The return value of the function depends on whether the range error
-was an overflow or an underflow.
-.P
-A floating result
-.I overflows
-if the result is finite,
-but is too large to represented in the result type.
-When an overflow occurs,
-the function returns the value
-.BR HUGE_VAL ,
-.BR HUGE_VALF ,
-or
-.BR HUGE_VALL ,
-depending on whether the function result type is
-.IR double ,
-.IR float ,
-or
-.IR "long double" .
-.I errno
-is set to
-.BR ERANGE ,
-and an "overflow"
-.RB ( FE_OVERFLOW )
-floating-point exception is raised.
-.P
-A floating result
-.I underflows
-if the result is too small to be represented in the result type.
-If an underflow occurs,
-a mathematical function typically returns 0.0
-(C99 says a function shall return "an implementation-defined value
-whose magnitude is no greater than the smallest normalized
-positive number in the specified type").
-.I errno
-may be set to
-.BR ERANGE ,
-and an "underflow"
-.RB ( FE_UNDERFLOW )
-floating-point exception may be raised.
-.P
-Some functions deliver a range error if the supplied argument value,
-or the correct function result, would be
-.IR subnormal .
-A subnormal value is one that is nonzero,
-but with a magnitude that is so small that
-it can't be presented in normalized form
-(i.e., with a 1 in the most significant bit of the significand).
-The representation of a subnormal number will contain one
-or more leading zeros in the significand.
-.SH NOTES
-The
-.I math_errhandling
-identifier specified by C99 and POSIX.1 is not supported by glibc.
-.\" See CONFORMANCE in the glibc 2.8 (and earlier) source.
-This identifier is supposed to indicate which of the two
-error-notification mechanisms
-.RI ( errno ,
-exceptions retrievable via
-.BR fetestexcept (3))
-is in use.
-The standards require that at least one be in use,
-but permit both to be available.
-The current (glibc 2.8) situation under glibc is messy.
-Most (but not all) functions raise exceptions on errors.
-Some also set
-.IR errno .
-A few functions set
-.IR errno ,
-but don't raise an exception.
-A very few functions do neither.
-See the individual manual pages for details.
-.P
-To avoid the complexities of using
-.I errno
-and
-.BR fetestexcept (3)
-for error checking,
-it is often advised that one should instead check for bad argument
-values before each call.
-.\" http://www.securecoding.cert.org/confluence/display/seccode/FLP32-C.+Prevent+or+detect+domain+and+range+errors+in+math+functions
-For example, the following code ensures that
-.BR log (3)'s
-argument is not a NaN and is not zero (a pole error) or
-less than zero (a domain error):
-.P
-.in +4n
-.EX
-double x, r;
-\&
-if (isnan(x) || islessequal(x, 0)) {
- /* Deal with NaN / pole error / domain error */
-}
-\&
-r = log(x);
-.EE
-.in
-.P
-The discussion on this page does not apply to the complex
-mathematical functions (i.e., those declared by
-.IR <complex.h> ),
-which in general are not required to return errors by C99
-and POSIX.1.
-.P
-The
-.BR gcc (1)
-.I "\-fno\-math\-errno"
-option causes the executable to employ implementations of some
-mathematical functions that are faster than the standard
-implementations, but do not set
-.I errno
-on error.
-(The
-.BR gcc (1)
-.I "\-ffast\-math"
-option also enables
-.IR "\-fno\-math\-errno" .)
-An error can still be tested for using
-.BR fetestexcept (3).
-.SH SEE ALSO
-.BR gcc (1),
-.BR errno (3),
-.BR fenv (3),
-.BR fpclassify (3),
-.BR INFINITY (3),
-.BR isgreater (3),
-.BR matherr (3),
-.BR nan (3)
-.P
-.I "info libc"