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msun: signed overflow in atan2

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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.

Closes #130

Submitted by:	Jeff Walden (@jswalden github PR #130)
Reviewed by:	bde
MFC After:	1 month
This commit is contained in:
eadler 2018-02-14 07:59:30 +00:00
parent 707bc0b7a7
commit b21ccf63f2
1 changed files with 1 additions and 1 deletions
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2
lib/msun/src/e_atan2.c
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@ -71,7 +71,7 @@ __ieee754_atan2(double y, double x)
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 */