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at 2025-12-13T14:24:22-08:00

Fix #458:  Fix spurious overflow in double-double multiply

Merge branch 'issue-458-double-double-mult-overflow' into 'master'

Fix #458:  Fix spurious overflow in double-double multiply

Closes #458

See merge request cmucl/cmucl!337
 	   (optimize (speed 3)))

   ;; If the numbers are too big, scale them done so SPLIT doesn't overflow.

   (multiple-value-bind (aa bb)

-      (values (if (> a +two970+)

+      (values (if (> (abs a) +two970+)

 		  (* a +two-53+)

 		  a)

-	      (if (> b +two970+)

+	      (if (> (abs b) +two970+)

 		  (* b +two-53+)

 		  b))

     (let ((p (* aa bb)))

 		(declare (optimize (inhibit-warnings 3)))

 	      ;; If the numbers was scaled down, we need to scale the

 	      ;; result back up.

-	      (when (> a +two970+)

+	      (when (> (abs a) +two970+)

 		(setf p (* p +two53+)

 		      e (* e +two53+)))

-	      (when (> b +two970+)

+	      (when (> (abs b) +two970+)

 		(setf p (* p +two53+)

 		      e (* e +two53+)))

 	      (values p e))))))))

 			     (x86::x87-floating-point-modes)))))

     (assert-true (typep new-mode 'x86::float-modes))

     (assert-equal new-mode (setf (x86::x87-floating-point-modes) new-mode))))

+

+

+

+;; Issue #458

+(define-test dd-mult-overflow

+  (:tag :issues)

+  (assert-equal -2w300

+		(* -2w300 1w0)))

Raymond Toy pushed to branch master at cmucl / cmucl

Commits:

2 changed files:

Changes: