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From: sla@helios (Steve Allen)
Newsgroups: comp.lang.fortran
Subject: operator precedence on FORTRAN 77
Summary: What does the standard say?
Keywords: unary minus, exponenation
Message-ID: <8980@saturn.ucsc.edu>
Date: 2 Sep 89 04:18:57 GMT
References: <3744@uwovax.uwo.ca>
Sender: usenet@saturn.ucsc.edu
Reply-To: sla@helios.ucsc.edu (Steve Allen)
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Organization: UC Observatories/Lick Observatory, Santa Cruz
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Which takes precedence, a unary minus, or an exponentiation?  This question
recently came up when one of our users ran a code which should have had more
parentheses.  The example is below.  My own impression is that the
Sun interpretation is the only one that makes sense, but I don't know
what the FORTRAN-77 standard requires.  Is there a correct interpretation?

	double precision  func1, func2, func3, func4
	func1 = 10.D0** -(3.D0)/2.D0
	func2 = 10.D0**(-(3.D0)/2.D0)
	func3 = 10.D0**  -3.D0 /2.D0
	func4 = 10.D0** - 3.D0 /2.D0
	write(*,*) func1, func2
	write(*,*) func3, func4
	end

Sun Fortran 1.x (x is either 0 or 1, I'm not sure)
on a Sun4 with SunOs 4.0.y (y is either 0 or 1, ditto) gives
    5.0000000000000D-04    3.1622776601684D-02
    5.0000000000000D-04    5.0000000000000D-04

VAX FORTRAN V4.7-271 on a MicroVax II with VMS V4.7 gives
 3.1622776601683793E-02  3.1622776601683793E-02
 3.1622776601683793E-02  3.1622776601683793E-02

Mips Computer Systems 1.31 Fortran on a SGI 4d/220 running IRIX V3.1F gives
   3.1622776601683790E-02  3.1622776601683790E-02
   3.1622776601683790E-02  3.1622776601683790E-02

Steve Allen
sla@helios.ucsc.edu
sla@portal.bitnet