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Re: problem building a GCJ-friendly GNU Crypto
- From: Roger Sayle <roger at eyesopen dot com>
- To: Mark Wielaard <mark at klomp dot org>
- Cc: raif at fl dot net dot au, <java at gcc dot gnu dot org>, <java-patches at gcc dot gnu dot org>, <gcc-patches at gcc dot gnu dot org>
- Date: Sat, 20 Sep 2003 13:33:37 -0600 (MDT)
- Subject: Re: problem building a GCJ-friendly GNU Crypto
Hi Mark,
> On Fri, 2003-09-19 at 16:37, Roger Sayle wrote:
> > A reduced test case would be great.
>
> The following should give:
> XO: 1
> But (with your patch applied) gives:
> X0: 65536.
>
> public class ConstTest
> {
> public static void main(String[] args)
> {
> byte[] in = new byte[] { 1, 0, 0, 0 };
> int i = 0;
> int X0 = (in[i++] & 0xFF)
> | (in[i++] & 0xFF) << 8
> | (in[i++] & 0xFF) << 16
> | in[i++] << 24;
> System.out.println("X0: " + X0);
> }
> }
Thanks for the test case. Looking at it I can immediately guess what
the problem is: the evaluation order of operands to binary operators.
A quick check of section 15.7.1 of the Java language specification
reveals that the semantics are indeed different from C and C++s which
allow side-effecting operands to be evaluated in arbitrary order.
I'm currently working on a patch to add an -fevaluation-order command
line option to GCC, that sets a flag_evaluation_order variable that
can be checked during constant folding to preserve left-to-right
evaluation order of binary expressions. This can then be enabled by
default by the java front-end, which should help make libbackend.a
more java friendly.
In the mean-time, the obvious fix is in[i], in[i+1], in[i+2] etc...
as recommended in section 15.7 in the java language specs. Hopefully,
I'll have a patch to fix the real problem ready to submit in a day
or two. Sorry for the inconvenience.
Roger
--
Roger Sayle, E-mail: roger@eyesopen.com
OpenEye Scientific Software, WWW: http://www.eyesopen.com/
Suite 1107, 3600 Cerrillos Road, Tel: (+1) 505-473-7385
Santa Fe, New Mexico, 87507. Fax: (+1) 505-473-0833