#65: Different results for EXPT between compiled and interpreted code --------------------+------------------------------------------------------- Reporter: rtoy | Owner: somebody Type: defect | Status: new Priority: major | Milestone: Component: Core | Version: 2012-12 Keywords: | --------------------+------------------------------------------------------- Description changed by rtoy: Old description:

Consider {{{ (defun sqr (x) (declare (type (complex double-float) x)) (expt x 2)) }}}

Compare the results: {{{ * (sqr #c(0d0 1d0)) #C(-1d0 0d0)

* (expt #c(0d0 1d0)) #C(-1.0d0 1.2246467991473532d-16) }}}

The difference is caused by a deftransform for {{{expt}}} that converts {{{(expt x 2)}}} to {{{(* x x)}}}.

Perhaps the {{{expt}}} should be modified to do the same transformation when the power is one of the special values in the deftransform? (The deftransform handles 2, 3, 4, and 1/2.)

New description: Consider {{{ (defun sqr (x) (declare (type (complex double-float) x)) (expt x 2)) }}} Compare the results: {{{ * (sqr #c(0d0 1d0)) #C(-1d0 0d0) * (expt #c(0d0 1d0) 2) #C(-1.0d0 1.2246467991473532d-16) }}} The difference is caused by a deftransform for {{{expt}}} that converts {{{(expt x 2)}}} to {{{(* x x)}}}. Perhaps the {{{expt}}} should be modified to do the same transformation when the power is one of the special values in the deftransform? (The deftransform handles 2, 3, 4, and 1/2 and their negatives.) -- -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/65#comment:1> cmucl <http://common-lisp.net/project/cmucl> Cmucl is a high-performance, free Common Lisp implementation.

#65: Different results for EXPT between compiled and interpreted code ---------------------+------------------------------------------------------ Reporter: rtoy | Owner: somebody Type: defect | Status: reopened Priority: major | Milestone: Component: Core | Version: 2012-12 Resolution: | Keywords: ---------------------+------------------------------------------------------ Changes (by rtoy): * status: closed => reopened * resolution: fixed => Comment: Some cases were missed in the previous patch. Here is a test that should cover all the cases. {{{ (defun test-expt-xfrm () (let (failures) (dolist (base '(2 2f0 2d0 2w0 #c(0 1) #c(0f0 1) #c(0d0 1) #c(0w0 1))) (dolist (power '(2 3 1/2 -2 -3 -1/2 5)) (dolist (power-type '(rational single-float double-float double- double-float (complex single-float) (complex double- float) (complex double-double-float))) (let* ((pp (coerce power power-type)) (interp (expt base pp)) (compiled (funcall (compile nil `(lambda (b) (declare (type ,(type- of base) b)) (expt b ,pp))) base))) (unless (= interp compiled) (push (list base pp interp compiled) failures) (format t "~S^~S =~% ~S~% ~S~%" base pp interp compiled)))))) failures)) }}} This should return {{{NIL}}} if everything is working correctly. -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/65#comment:3> cmucl <http://common-lisp.net/project/cmucl> Cmucl is a high-performance, free Common Lisp implementation.