#15: x86 double-float issue
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Reporter: rtoy | Owner: somebody
Type: defect | Status: new
Priority: minor | Milestone:
Component: Core | Version: 19d
Keywords: |
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Consider this sample code
{{{
(defun rbug (z tt betain beta)
(declare (double-float z tt betain beta)
(optimize (speed 3) (safety 0)))
(= (* (* (* z tt) betain) beta) z))
}}}
Compile it and run:
{{{
(rbug 5.562684646268004d-309 (1+ double-float-epsilon) .5d0 2d0)
}}}
This is t on sparc, nil on x86.
This is caused by x86 issues with double-float (53-bit) precision and the
extra range of the exponent in long-double (64-bit) format. Denormals in
this format are not handled the same as denormals on sparc or ppc.
There is a fix for this. When computing x*y, we scale x by an appropriate
value, multiply by y, and scale back. This will produce the correctly
rounded denormal. The only issue would be the exponent range. That is
fixed by storing the number to memory and reloaded. (This solution taken
from a proposed solution for Java numerics).
This could be easily implemented, but potentially slows down double-float
arithmetic by a factor of 2-4 times. I don't think we want to do that.
--
Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/15>
cmucl <http://common-lisp.net/project/cmucl>
cmucl
#14: cmucl.css
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Reporter: heller | Owner: somebody
Type: defect | Status: new
Priority: trivial | Milestone:
Component: Core | Version: 19d
Keywords: |
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many of the HTML files in cmu-user-html.tgz link to the cmucl.css
stylesheet, but it's not in the tarball.
--
Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/14>
cmucl <http://common-lisp.net/project/cmucl>
cmucl
