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at 2025-08-13T15:06:30-07:00

Set 64-bit precision (80-bit float) in call-out

Add some tests for the special functions where we were computing the
incorrect value when the precision was not set to 64-bit (80-bit
float).

   #+core-math

   (:temporary (:sc unsigned-stack) fpu-cw)

   #+core-math

-  (:temporary (:sc unsigned-reg) temp-cw)

+  (:temporary (:sc unsigned-reg :offset esi-offset) temp-cw)

   (:node-var node)

   (:vop-var vop)

   (:save-p t)

     #+core-math

     (progn

       ;; Save the x87 FPU control word.  Then modify it to set the

-      ;; precision bits to double (2).

+      ;; precision bits to 3 for 64-bit mantissas for 80-bit

+      ;; arithmetic.  If we don't some of some special functions

+      ;; return incorrect values because the x87 precision was set to

+      ;; single.

       (inst fnstcw save-fpu-cw)

       (move temp-cw save-fpu-cw)

       (inst and temp-cw (dpb 0 (byte 2 8) #xffff)) ; Zap the precision control bits

-      (inst or temp-cw (dpb 2 (byte 2 8) 0)) ; Set precision control to double

+      (inst or temp-cw (dpb 3 (byte 3 8) 0)) ; Set precision control bits

       (move fpu-cw temp-cw)

       (inst fldcw fpu-cw)		; New CW

       )

               (tanh #c(200w0 200w0))))

+(define-test cos-tiny

+    (:tag issues)

+  ;; This test comes from the Maxima testsuite where core-math was not

+  ;; computing cos(8.881784197001252d-16) correctly.  It should be

+  ;; exactly 1.  We were getting one bit less.

+  (assert-eql 1d0

+	      (cos (kernel:make-double-float 1020264448 0))))

+

+(define-test log.special-value

+    (:tag issues)

+  ;; This test comes from the Maxima testsuite where core-math was not

+  ;; computing log(0.6899991035461426d0) => -0.37106498060016496d0.

+  ;; The computed result looked it had like a single-precision accuracy.

+  (assert-eql -0.37106498060016496d0

+	      (kernel:%log (kernel:make-double-float (+ 1071644672 398457) 0))))

Raymond Toy pushed to branch issue-425-correctly-rounded-math-functions at cmucl / cmucl

Commits:

2 changed files:

Changes: