In article <caf6rxgkptzu_+m2howvqb5wxdafdrdl2yqj0vcy2lovswt6...@mail.gmail.com>, Eitan Adler <li...@eitanadler.com> wrote: >Hi all, > >I'd like to commit the patch below. Does anyone have concerns with it? > >Previous discussion: >https://lists.freebsd.org/pipermail/freebsd-numerics/2018-February/thread.html >https://marc.info/?l=openbsd-tech&m=151859583112854&w=2 > >Original submission: https://github.com/freebsd/freebsd/pull/130 > > >=== > >As a component of atan2(y, x), the case of x == 1.0 is farmed out to >atan(y). The current implementation of this comparison is vulnerable >to signed integer underflow (that is, undefined behavior), and it's >performed in a somewhat more complicated way than it need be. Change >it to not be quite so cute, rather directly comparing the high/low >bits of x to the specific IEEE-754 bit pattern that encodes 1.0. > >Note that while there are three different e_atan* files in the >relevant directory, only this one needs fixing. e_atan2f.c already >compares against the full bit pattern encoding 1.0f, while >e_atan2l.cuses bitwise-ands/ors/nots and so doesn't require a change. >=== > > > >Index: e_atan2.c >=================================================================== >RCS file: /cvs/src/lib/libm/src/e_atan2.c,v >retrieving revision 1.13 >diff -u -r1.13 e_atan2.c >--- e_atan2.c 12 Sep 2016 19:47:02 -0000 1.13 >+++ e_atan2.c 14 Feb 2018 08:06:05 -0000 >@@ -64,7 +64,7 @@ > if(((ix|((lx|-lx)>>31))>0x7ff00000)|| > ((iy|((ly|-ly)>>31))>0x7ff00000)) /* x or y is NaN */ > return x+y; >- if(((hx-0x3ff00000)|lx)==0) return atan(y); /* x=1.0 */ >+ if(hx==0x3ff00000&&lx==0) return atan(y); /* x=1.0 */ > m = ((hy>>31)&1)|((hx>>30)&2); /* 2*sign(x)+sign(y) */ > > /* when y = 0 */
Go for it. christos