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diff --git a/man3/fenv.3 b/man3/fenv.3 new file mode 100644 index 0000000..653ba03 --- /dev/null +++ b/man3/fenv.3 @@ -0,0 +1,335 @@ +'\" t +.\" Copyright (c) 2000 Andries Brouwer (aeb@cwi.nl) +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" 2000-08-14 added GNU additions from Andreas Jaeger +.\" 2000-12-05 some changes inspired by acahalan's remarks +.\" +.TH fenv 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +feclearexcept, fegetexceptflag, feraiseexcept, fesetexceptflag, +fetestexcept, fegetenv, fegetround, feholdexcept, fesetround, +fesetenv, feupdateenv, feenableexcept, fedisableexcept, +fegetexcept \- floating-point rounding and exception handling +.SH LIBRARY +Math library +.RI ( libm ", " \-lm ) +.SH SYNOPSIS +.nf +.B #include <fenv.h> +.PP +.BI "int feclearexcept(int " excepts ); +.BI "int fegetexceptflag(fexcept_t *" flagp ", int " excepts ); +.BI "int feraiseexcept(int " excepts ); +.BI "int fesetexceptflag(const fexcept_t *" flagp ", int " excepts ); +.BI "int fetestexcept(int " excepts ); +.PP +.B "int fegetround(void);" +.BI "int fesetround(int " rounding_mode ); +.PP +.BI "int fegetenv(fenv_t *" envp ); +.BI "int feholdexcept(fenv_t *" envp ); +.BI "int fesetenv(const fenv_t *" envp ); +.BI "int feupdateenv(const fenv_t *" envp ); +.fi +.SH DESCRIPTION +These eleven functions were defined in C99, and describe the handling +of floating-point rounding and exceptions (overflow, zero-divide, etc.). +.SS Exceptions +The +.I divide-by-zero +exception occurs when an operation on finite numbers +produces infinity as exact answer. +.PP +The +.I overflow +exception occurs when a result has to be represented as a +floating-point number, but has (much) larger absolute value than the +largest (finite) floating-point number that is representable. +.PP +The +.I underflow +exception occurs when a result has to be represented as a +floating-point number, but has smaller absolute value than the smallest +positive normalized floating-point number (and would lose much accuracy +when represented as a denormalized number). +.PP +The +.I inexact +exception occurs when the rounded result of an operation +is not equal to the infinite precision result. +It may occur whenever +.I overflow +or +.I underflow +occurs. +.PP +The +.I invalid +exception occurs when there is no well-defined result +for an operation, as for 0/0 or infinity \- infinity or sqrt(\-1). +.SS Exception handling +Exceptions are represented in two ways: as a single bit +(exception present/absent), and these bits correspond in some +implementation-defined way with bit positions in an integer, +and also as an opaque structure that may contain more information +about the exception (perhaps the code address where it occurred). +.PP +Each of the macros +.BR FE_DIVBYZERO , +.BR FE_INEXACT , +.BR FE_INVALID , +.BR FE_OVERFLOW , +.B FE_UNDERFLOW +is defined when the implementation supports handling +of the corresponding exception, and if so then +defines the corresponding bit(s), so that one can call +exception handling functions, for example, using the integer argument +.BR FE_OVERFLOW | FE_UNDERFLOW . +Other exceptions may be supported. +The macro +.B FE_ALL_EXCEPT +is the bitwise OR of all bits corresponding to supported exceptions. +.PP +The +.BR feclearexcept () +function clears the supported exceptions represented by the bits +in its argument. +.PP +The +.BR fegetexceptflag () +function stores a representation of the state of the exception flags +represented by the argument +.I excepts +in the opaque object +.IR *flagp . +.PP +The +.BR feraiseexcept () +function raises the supported exceptions represented by the bits in +.IR excepts . +.PP +The +.BR fesetexceptflag () +function sets the complete status for the exceptions represented by +.I excepts +to the value +.IR *flagp . +This value must have been obtained by an earlier call of +.BR fegetexceptflag () +with a last argument that contained all bits in +.IR excepts . +.PP +The +.BR fetestexcept () +function returns a word in which the bits are set that were +set in the argument +.I excepts +and for which the corresponding exception is currently set. +.SS Rounding mode +The rounding mode determines how the result of floating-point operations +is treated when the result cannot be exactly represented in the significand. +Various rounding modes may be provided: +round to nearest (the default), +round up (toward positive infinity), +round down (toward negative infinity), and +round toward zero. +.PP +Each of the macros +.BR FE_TONEAREST , +.BR FE_UPWARD , +.BR FE_DOWNWARD , +and +.B FE_TOWARDZERO +is defined when the implementation supports getting and setting +the corresponding rounding direction. +.PP +The +.BR fegetround () +function returns the macro corresponding to the current +rounding mode. +.PP +The +.BR fesetround () +function sets the rounding mode as specified by its argument +and returns zero when it was successful. +.PP +C99 and POSIX.1-2008 specify an identifier, +.BR FLT_ROUNDS , +defined in +.IR <float.h> , +which indicates the implementation-defined rounding +behavior for floating-point addition. +This identifier has one of the following values: +.TP +.B \-1 +The rounding mode is not determinable. +.TP +.B 0 +Rounding is toward 0. +.TP +.B 1 +Rounding is toward nearest number. +.TP +.B 2 +Rounding is toward positive infinity. +.TP +.B 3 +Rounding is toward negative infinity. +.PP +Other values represent machine-dependent, nonstandard rounding modes. +.PP +The value of +.B FLT_ROUNDS +should reflect the current rounding mode as set by +.BR fesetround () +(but see BUGS). +.SS Floating-point environment +The entire floating-point environment, including +control modes and status flags, can be handled +as one opaque object, of type +.IR fenv_t . +The default environment is denoted by +.B FE_DFL_ENV +(of type +.IR "const fenv_t\ *" ). +This is the environment setup at program start and it is defined by +ISO C to have round to nearest, all exceptions cleared and a nonstop +(continue on exceptions) mode. +.PP +The +.BR fegetenv () +function saves the current floating-point environment in the object +.IR *envp . +.PP +The +.BR feholdexcept () +function does the same, then clears all exception flags, +and sets a nonstop (continue on exceptions) mode, +if available. +It returns zero when successful. +.PP +The +.BR fesetenv () +function restores the floating-point environment from +the object +.IR *envp . +This object must be known to be valid, for example, the result of a call to +.BR fegetenv () +or +.BR feholdexcept () +or equal to +.BR FE_DFL_ENV . +This call does not raise exceptions. +.PP +The +.BR feupdateenv () +function installs the floating-point environment represented by +the object +.IR *envp , +except that currently raised exceptions are not cleared. +After calling this function, the raised exceptions will be a bitwise OR +of those previously set with those in +.IR *envp . +As before, the object +.I *envp +must be known to be valid. +.SH RETURN VALUE +These functions return zero on success and nonzero if an error occurred. +.\" Earlier seven of these functions were listed as returning void. +.\" This was corrected in Corrigendum 1 (ISO/IEC 9899:1999/Cor.1:2001(E)) +.\" of the C99 Standard. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.nh +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR feclearexcept (), +.BR fegetexceptflag (), +.BR feraiseexcept (), +.BR fesetexceptflag (), +.BR fetestexcept (), +.BR fegetround (), +.BR fesetround (), +.BR fegetenv (), +.BR feholdexcept (), +.BR fesetenv (), +.BR feupdateenv (), +.BR feenableexcept (), +.BR fedisableexcept (), +.BR fegetexcept () +T} Thread safety T{ +.na +.nh +MT-Safe +T} +.TE +.sp 1 +.hy +.SH STANDARDS +C11, POSIX.1-2008, IEC 60559 (IEC 559:1989), ANSI/IEEE 854. +.SH HISTORY +C99, POSIX.1-2001. +glibc 2.1. +.SH NOTES +.SS glibc notes +If possible, the GNU C Library defines a macro +.B FE_NOMASK_ENV +which represents an environment where every exception raised causes a +trap to occur. +You can test for this macro using +.BR #ifdef . +It is defined only if +.B _GNU_SOURCE +is defined. +The C99 standard does not define a way to set individual bits in the +floating-point mask, for example, to trap on specific flags. +Since glibc 2.2, glibc supports the functions +.BR feenableexcept () +and +.BR fedisableexcept () +to set individual floating-point traps, and +.BR fegetexcept () +to query the state. +.PP +.nf +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" +.B "#include <fenv.h>" +.PP +.BI "int feenableexcept(int " excepts ); +.BI "int fedisableexcept(int " excepts ); +.B "int fegetexcept(void);" +.fi +.PP +The +.BR feenableexcept () +and +.BR fedisableexcept () +functions enable (disable) traps for each of the exceptions represented by +.I excepts +and return the previous set of enabled exceptions when successful, +and \-1 otherwise. +The +.BR fegetexcept () +function returns the set of all currently enabled exceptions. +.SH BUGS +C99 specifies that the value of +.B FLT_ROUNDS +should reflect changes to the current rounding mode, as set by +.BR fesetround (). +Currently, +.\" Aug 08, glibc 2.8 +this does not occur: +.B FLT_ROUNDS +always has the value 1. +.\" See http://gcc.gnu.org/ml/gcc/2002-02/msg01535.html +.SH SEE ALSO +.BR math_error (7) |