[Search for users] [Overall Top Noters] [List of all Conferences] [Download this site]

Conference turris::fortran

Title:	Digital Fortran
Notice:	Read notes 1.* for important information
Moderator:	QUARK::LIONEL

Created:	Thu Jun 01 1995
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	1333
Total number of notes:	6734

1238.0. "floating invalid operation on WNT" by COL01::VSEMUSCHIN (Duck and Recover !) Tue Mar 25 1997 07:08

Customer has following problem:

c
c DEC Fortran for WNT version 1.2 tested on both
c WNT 4.0 and 3.51
c
	program power3
	implicit double precision (a-z)

c following works:

	r=-2**3
	write(*,*)r

c following produces:
c forrtl: severe: Program Exception - floating invalind operation

	x=-2.
	y=3.
	w=x**y
	write(*,*)w

	end

I suspect RTL errors ...
Help !

=Seva

T.R Title User Personal
Name Date Lines

1238.1 use /check=nopower to get C semantics from ** TLE::WHITLOCK Stan Whitlock Tue Mar 25 1997 08:13 26

T.R	Title	User	Personal Name	Date	Lines
1238.1	use /check=nopower to get C semantics from **	TLE::WHITLOCK	Stan Whitlock	`Tue Mar 25 1997 08:13`	26
	there are several things going on here: >> r=-2.3. is evaluated as -(2.3.) since takes precedence over unary - in standard Fortran rules. So the answer is -8. >> (-2.)3. is illegal Fortran, both by Fortran 77 and Fortran 90. Therefore you get an error at run-time. But DFANT v1.2 has the "/check=nopower" switch, which changes the semantics of to be like C, ie, o 0.0. == 1. o negative number to an odd integer power works so if you compile with "/check=nopower" {the deafult is "/check=power"}, you'll get -8. from (-2.)**3. "/check=[no]power" is available in f90 and f77 on Alpha/VMS, Alpha/UNIX, and Alpha/NT {spelled appropriately for the platform}. /Stan

there are several things going on here:

>>	r=-2.**3.

is evaluated as -(2.**3.) since ** takes precedence over unary - in standard
Fortran rules.  So the answer is -8.

>>	(-2.)**3.

is illegal Fortran, both by Fortran 77 and Fortran 90.  Therefore you get an
error at run-time.

But DFANT v1.2 has the "/check=nopower" switch, which changes the semantics of
** to be like C, ie, 

    o	0.**0.  == 1.

    o	negative number to an odd integer power works

so if you compile with "/check=nopower" {the deafult is "/check=power"}, you'll
get -8. from (-2.)**3.

"/check=[no]power" is available in f90 and f77 on Alpha/VMS, Alpha/UNIX, and
Alpha/NT {spelled appropriately for the platform}.

/Stan