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From: pmontgom@MATH.UCLA.EDU
Newsgroups: comp.lang.fortran,comp.bugs.4bsd
Subject: RSHIFT doesn't always sign extend
Message-ID: <11219@shemp.UCLA.EDU>
Date: 9 Feb 88 02:16:07 GMT
Sender: root@CS.UCLA.EDU
Reply-To: pmontgom@MATH.UCLA.EDU (Peter Montgomery)
Organization: UCLA Mathematics Department
Lines: 28

C		The manual page BIT(3F) states "Rshift, or lshift
C       with a negative nbits, is an arithmetic right shift with 
C       sign extension."  Accordingly, both LSHIFT(-4, -2) and 
C	RSHIFT(-4, 2) should return -1.  Both do return -1
C       when used with constant arguments.  But when the
C	arguments to RSHIFT are variables, it does not do sign
C	extension (instead, it generates an extxv instruction).
C
C		The following output was obtained on a VAX 750.
C	The "-v" option to f77 produces "Berkeley F77,
C	version 2.0 (4.3 bsd, SCCS level 6)."

* Constant LSHIFT(-4, -2) =   -1
* Variable LSHIFT(-4, -2) =   -1
* Constant RSHIFT(-4, +2) =   -1
* Variable RSHIFT(-4, +2) =   1073741823

	program SHIFTS
	integer two, four
	data two/2/, four/4/

	print * , 'Constant LSHIFT(-4, -2) = ', LSHIFT(-4, -2)
	print * , 'Variable LSHIFT(-4, -2) = ', LSHIFT(-four, -two)
	print * , 'Constant RSHIFT(-4, +2) = ', RSHIFT(-4, +2)
	print * , 'Variable RSHIFT(-4, +2) = ', RSHIFT(-four, +two)
	end
--------
         pmontgom@sdcrdcf.UUCP
         pmontgom@julia.MATH.UCLA.EDU