F77_IEEE_ENVIRONMENT(3F) — FORTRAN LIBRARY ROUTINES

NAME

IEEE environment - mode, status, and signal handling subprograms for IEEE arithmetic

SYNOPSIS

#include <f77/f77_floatingpoint.h>

integer function ieee_flags(action,mode,in,out)
character∗(∗) action, mode, in, out

integer function ieee_handler(action,exception,hdl)
character∗(∗) action, exception
sigfpe_handler_type hdl

sigfpe_handler_type function sigfpe(code, hdl)
sigfpe_code_type code
sigfpe_handler_type hdl

DESCRIPTION

These subprograms provide modes and status required to fully exploit ANSI/IEEE Std 754-1985 arithmetic in a FORTRAN program. They correspond closely to the functions ieee_flags(3M), ieee_handler(3M), and sigfpe(3).

EXAMPLES

The following examples illustrate syntax.

integer ieeer
character∗1 mode, out, in
ieeer = ieee_flags(’clearall’,mode, in, out)

sets ieeer to 0, rounding direction to ’nearest’, rounding precision to ’extended’, and all accrued exception-occurred status to zero.

character∗1 out, in
ieeer = ieee_flags(’clear’,’direction’, in, out)

sets ieeer to 0, and rounding direction to ’nearest’.

character∗1 out
ieeer = ieee_flags(’set’,’direction’,’tozero’,out)

sets ieeer to 0 and the rounding direction to ’tozero’ unless the hardware does not support directed rounding modes; then ieeer is set to 1.

character∗16 out
ieeer = ieee_flags(’clear’,’exception’,’all’,out)

sets ieeer to 0 and clears all accrued exception-occurred bits. If subsequently overflow, invalid, and inexact exceptions are generated then

character∗16 out
ieeer = ieee_flags(’get’,’exception’,’overflow’,out)

sets ieeer to 25 and out to ’overflow’.

A user-specified signal handler might look like this:

integer function sample_handler ( sig, code, sigcontext )
integer sig
integer code
integer sigcontext(5)
cSample user-written sigfpe code handler.
cPrints a message and terminates.
csig .eq. SIGFPE always.
cThe structure of sigcontext is defined in <signal.h>.
print ∗, ’ieee exception code ’, loc(code), ’ occurred at pc ’, sigcontext(4)
call abort
end
and it might be set up like this:
external sample_handler
integer ieeer
ieeer = ieee_handler ( ’set’, ’overflow’, sample_handler )
if (ieeer .ne. 0) print ∗,’ ieee_handler can not set overflow ’

NOTE: UNIX invokes signal handlers by passing sig and code by value. If you write a signal handler function in FORTRAN as in the example, you can access these values with the loc function.

FILES

/usr/include/f77/f77_floatingpoint.h
/usr/lib/libm.a

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