1.4.26 ieee_flags,ieee_handler,sigfpe: IEEE Arithmetic
These subprograms provide modes and status required to fully exploit ANSI/IEEE Standard 754-1985 arithmetic in a Fortran program. They correspond closely to the functions ieee_flags(3M), ieee_handler(3M), and sigfpe(3).
Table 1–5 IEEE Arithmetic Support Routines|
ieeer = ieee_flags( action,mode,in,out ) ieeer = ieee_handler(action,exception,hdl ) ieeer = sigfpe( code, hdl ) |
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action |
character |
Input |
|
code |
sigfpe_code_type |
Input |
|
mode |
character |
Input |
|
in |
character |
Input |
|
exception |
character |
Input |
|
hdl |
sigfpe_handler_type |
Input |
|
out |
character |
Output |
|
Return value |
INTEGER*4 |
Output |
See the Numerical Computation Guide for details on how these functions can be used strategically.
If you use sigfpe, you must do your own setting of the corresponding trap-enable-mask bits in the floating-point status register. The details are in the SPARC architecture manual. The libm function ieee_handler sets these trap-enable-mask bits for you.
The character keywords accepted for mode and exception depend on the value of action.
Table 1–6 ieee_flags( action , mode , in , out) Parameters and Actions|
action = ’clearall’ |
mode, in, out, unused; returns 0 |
|
|
action = ’clear’ clear mode, in out is unused; returns 0 |
mode = ’direction’ | |
|
mode = ’exception’ |
in = ’inexact’ or ’division’ or ’underflow’ or ’overflow’ or ’invalid’ or ’all’ or ’common’ |
|
|
action = ’set’ set floating-point mode, in out is unused; returns 0 |
mode = ’direction’ |
in = ’nearest’ or ’tozero’ or ’positive’ or ’negative’ |
|
mode = ’exception’ |
in = ’inexact’ or ’division’ or ’underflow’ or ’overflow’ or ’invalid’ or ’all’ or ’common’ |
|
|
action = ’get’ test mode settings in, out may be blank or one of the settings to test returns the current setting depending on mode, or ’not available’ The function returns 0 or the current exception flags if mode = ’exception’ |
mode =’direction’ |
out = ’nearest’ or ’tozero’ or ’positive’ or ’negative’ |
|
mode =’exception’ |
out = ’inexact’ or ’division’ or ’underflow’ or ’overflow’ or ’invalid’ or ’all’ or ’common’ |
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Table 1–7 ieee_handler( action , in , out) Parameters
|
action = ’clear’ clear user exception handing of in; out is unused |
in = ’inexact’ or ’division’ or ’underflow’ or ’overflow’ or ’invalid’ or ’all’ or ’common’ |
|
action = ’set’ set user exception handing of in; out is address of handler routine, or SIGFPE_DEFAULT, or SIGFPE_ABORT, or SIGFPE_IGNORE defined in floating point.h |
in = ’inexact’ or ’division’ or ’underflow’ or ’overflow’ or ’invalid’ or ’all’ or ’common’ |
Example 1: Set rounding direction to round toward zero, unless the hardware does not support directed rounding modes:
INTEGER*4 ieeer
character*1 mode, out, in
ieeer = ieee_flags( ’set’, ’direction’, ’tozero’, out )
|
Example 2: Clear rounding direction to default (round toward nearest):
character*1 out, in
ieeer = ieee_flags(’clear’,’direction’, in, out )
|
Example 3: Clear all accrued exception-occurred bits:
character*18 out
ieeer = ieee_flags( ’clear’, ’exception’, ’all’, out )
|
Example 4: Detect overflow exception as follows:
character*18 out
ieeer = ieee_flags( ’get’, ’exception’, ’overflow’, out )
if (out .eq. ’overflow’ ) stop ’overflow’
|
The above code sets out to overflow and ieeer to 25 (this value is platform dependent). Similar coding detects exceptions, such as invalid or inexact.
Example 5: hand1.f, write and use a signal handler:
external hand
real r / 14.2 /, s / 0.0 /
i = ieee_handler( ’set’, ’division’, hand )
t = r/s
end
INTEGER*4 function hand ( sig, sip, uap )
INTEGER*4 sig, address
structure /fault/
INTEGER*4 address
end structure
structure /siginfo/
INTEGER*4 si_signo
INTEGER*4 si_code
INTEGER*4 si_errno
record /fault/ fault
end structure
record /siginfo/ sip
address = sip.fault.address
write (*,10) address
10 format(’Exception at hex address ’, z8 )
end
|
Change the declarations for address and function hand to INTEGER*8 to enable Example 5 in a 64-bit, SPARC environment (-m64)
See the Numerical Computation Guide. See also: floatingpoint(3), signal(3), sigfpe(3), floatingpoint(3F), ieee_flags(3M), and ieee_handler(3M).
1.4.26.1 floatingpoint.h: Fortran IEEE Definitions
The header file floatingpoint.h defines constants and types used to implement standard floating-point according to ANSI/IEEE Std 754-1985.
Include the file in a Fortran 95 source program as follows:
#include "floatingpoint.h" |
Use of this include file requires preprocessing prior to Fortran compilation. The source file referencing this include file will automatically be preprocessed if the name has a .F, .F90 or .F95 extension.
|
fp_direction_type |
The type of the IEEE rounding direction mode. The order of enumeration varies according to hardware. |
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sigfpe_code_type |
The type of a SIGFPE code. |
|
sigfpe_handler_type |
The type of a user-definable SIGFPE exception handler called to handle a particular SIGFPE code. |
|
SIGFPE_DEFAULT |
A macro indicating default SIGFPE exception handling: IEEE exceptions to continue with a default result and to abort for other SIGFPE codes. |
|
SIGFPE_IGNORE |
A macro indicating an alternate SIGFPE exception handling, namely to ignore and continue execution. |
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SIGFPE_ABORT |
A macro indicating an alternate SIGFPE exception handling, namely to abort with a core dump. |
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N_IEEE_EXCEPTION |
The number of distinct IEEE floating-point exceptions. |
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fp_exception_type |
The type of the N_IEEE_EXCEPTION exceptions. Each exception is given a bit number. |
|
fp_exception_field_type |
The type intended to hold at least N_IEEE_EXCEPTION bits corresponding to the IEEE exceptions numbered by fp_exception_type. Thus, fp_inexact corresponds to the least significant bit and fp_invalid to the fifth least significant bit. Some operations can set more than one exception. |
IEEE Classification:
|
fp_class_type |
A list of the classes of IEEE floating-point values and symbols. |
Refer to the Numerical Computation Guide. See also ieee_environment(3F).
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