[Bug 294692] [PATCH] lib/msun: Replaced manual checks with isnan()

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D294692

--- Comment #1 from Steve Kargl <[email protected]> ---
Jesus, this looks okay to me.  But, I do wonder about one issue
and have one suggestion.

Issue: All of the bitwise expressions that have been replaced
worked even if a user compiled libm with -ffast-math.  I
suspect the new changes will be optimized out.  I don't know
if we need to be paranoid about this or not; worse yet, I do=20
not know how to warn users to be careful with compiler options.

Suggestion:  In the changed routines, we either assign parameters
to internal variables or directly access the bits before the
isnan() tests.  For example,

 double
 nextafter(double x, double y)
 {
        volatile double t;
        int32_t hx,hy,ix,iy;
        u_int32_t lx,ly;

        EXTRACT_WORDS(hx,lx,x);
        EXTRACT_WORDS(hy,ly,y);
        ix =3D hx&0x7fffffff;             /* |x| */
        iy =3D hy&0x7fffffff;             /* |y| */

-       if(((ix>=3D0x7ff00000)&&((ix-0x7ff00000)|lx)!=3D0) ||   /* x is nan=
 */
-          ((iy>=3D0x7ff00000)&&((iy-0x7ff00000)|ly)!=3D0))     /* y is nan=
 */
+       if(isnan(x) || isnan(y))     /* x or y is nan */
           return x+y;
        if(x=3D=3Dy) return y;              /* x=3Dy, return y */
        if((ix|lx)=3D=3D0) {                        /* x =3D=3D 0 */
            INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */

You can move the isnan() test to before EXTRACT_WORDS() in the above
as well as the 'x =3D=3D y' test.  That is, extract the bits when we need
them.

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