#20: Modular arith bug? ---------------------+------------------------------------------------------ Reporter: rtoy | Owner: somebody Type: defect | Status: new Priority: major | Milestone: Component: Core | Version: 19e Resolution: | Keywords: ---------------------+------------------------------------------------------ Old description:

{{{ (defun mat3neg (tt v) (ldb (byte 32 0) (ash v (- tt))))

(defun mat3neg-a (tt v) (logand #xffffffff (ash v (- tt))))

(defun zot (z2) (declare (type (unsigned-byte 32) z2) (optimize speed (safety 0))) (mat3neg -28 z2))

(defun zot-a (z2) (declare (type (unsigned-byte 32) z2) (optimize speed (safety 0))) (mat3neg-a -28 z2)) }}}

Compile {{{zot}}} and there are lots of compiler notes, from {{{mat3neg}}}. But compile {{{zot-a}}} and there's just one for boxing up the result.

However, {{{zot}}} and {{{zot-a}}} are functionally identical, so {{{zot}}} and {{{zot-a}}} should produce the same code. But {{{zot}}} has to do a full call to {{{ash}}} and {{{two-arg-and}}}.

The {{{ldb}}} must be confusing the compiler somehow.

New description: {{{ (declaim (inline mat3neg mat3neg-a)) (defun mat3neg (tt v) (ldb (byte 32 0) (ash v (- tt)))) (defun mat3neg-a (tt v) (logand #xffffffff (ash v (- tt)))) (defun zot (z2) (declare (type (unsigned-byte 32) z2) (optimize speed (safety 0))) (mat3neg -28 z2)) (defun zot-a (z2) (declare (type (unsigned-byte 32) z2) (optimize speed (safety 0))) (mat3neg-a -28 z2)) }}} Compile {{{zot}}} and there are lots of compiler notes, from {{{mat3neg}}}. But compile {{{zot-a}}} and there's just one for boxing up the result. However, {{{zot}}} and {{{zot-a}}} are functionally identical, so {{{zot}}} and {{{zot-a}}} should produce the same code. But {{{zot}}} has to do a full call to {{{ash}}} and {{{two-arg-and}}}. The {{{ldb}}} must be confusing the compiler somehow. -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/20> cmucl <http://common-lisp.net/project/cmucl> cmucl

#20: Modular arith bug? ---------------------+------------------------------------------------------ Reporter: rtoy | Owner: somebody Type: defect | Status: closed Priority: major | Milestone: Component: Core | Version: 19e Resolution: fixed | Keywords: ---------------------+------------------------------------------------------ Changes (by rtoy): * resolution: => fixed * status: new => closed Comment: This particular issue is fixed and should work as expected in the 2008-09 snapshot. The workaround was to change %ldb to optimize the expression at compile-time as much as possible. Closing this particular issue. -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/20> cmucl <http://common-lisp.net/project/cmucl> cmucl