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

Commits:

• d2210864
  by Raymond Toy at 2026-02-16T14:31:08-08:00

  Fix #473:  Signal underflow with cr_exp
  
  Explicitly signal underflow (if enabled) when calling `kernel:%exp`
  with an arg that would cause exp to underflow.  The constant used is
  taken from the source code for core-math exp.c.
  
  Update the in fdlibm to use `with-float-traps-enabled` instead of the
  weird way we were doing it.
  

• c84c6c27
  by Raymond Toy at 2026-02-16T18:52:48-08:00

  Make core-math exp silently return NaN when given NaN
  
  This makes exp match what many other core-math routines do with NaN,
  like log, sin, tan, and sinh, which silently return NaN.
  
  This also makes it match what fdlibm does, as mentioned in the
  comments in e_exp.c.
  

• 72096452
  by Raymond Toy at 2026-02-17T10:51:19-08:00

  Merge branch 'master' into issue-473-make-cr-exp-signal-underflow
  

• 7fa0f3c1
  by Raymond Toy at 2026-02-17T19:59:33-08:00

  Merge branch 'issue-473-make-cr-exp-signal-underflow' into issue-425-correctly-rounded-math-functions-single-float
  

2 changed files:

• src/lisp/irrat.c
• tests/fdlibm.lisp

Changes:

  */

 #define MAYBE_SIGNAL_INVALID(test, val)		\

-    if ((test)) {				\ 

+    if ((test)) {				\

         return fdlibm_setexception(val, FDLIBM_INVALID);	\

     }

 lisp_exp(double x)

 {

 #ifdef FEATURE_CORE_MATH

+    /*

+     * For consistency, silently return NaN when x is NaN.  Do not

+     * signal an invalid operation, even if invalid operation trap is

+     *  enabled.  This is what fdlibm does, and also what many of the

+     *  other core-math routines do.

+     */

+

+    if (isnan(x)) {

+	return x;

+    }

+    

+    /*

+     * Can't depend on cr_exp to signal underflow.  It seems the

+     * underflow has been constant-folded to zero.  Hence, check for

+     * underflow here and explicitly signal an underflow.  The

+     * constant here is from core-math exp.c.

+     */

+    if (x <= -0x1.74910d52d3052p+9) {

+	return fdlibm_setexception(0.0, FDLIBM_UNDERFLOW);

+    }

+

     return cr_exp(x);

 #else    

     return __ieee754_exp(x);

   (ext:with-float-traps-masked (:overflow)

     (assert-equal ext:double-float-positive-infinity

 		  (kernel:%exp 710d0)))

-  (let ((modes (ext:get-floating-point-modes)))

-    (unwind-protect

-	 (progn

-	   (ext:set-floating-point-modes :traps '(:underflow))

-	   (assert-error 'floating-point-underflow

-			 (kernel:%exp -1000d0)))

-      (apply #'ext:set-floating-point-modes modes)))

+  (ext:with-float-traps-enabled (:underflow)

+    (assert-error 'floating-point-underflow

+		  (kernel:%exp -1000d0)))

   (let ((x (scale-float 1d0 -29))

 	(x0 0d0))

     ;; exp(x) = x, |x| < 2^-28, with inexact exception unlees x = 0