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Simplified the fix in rev.1.3. Instead of using long double for

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TWO52[sx] to trick gcc into correctly converting TWO52[sx]+x to double
on assignment to "double w", force a correct assignment by assigning
to *(double *)&w.  This is cleaner and avoids the double rounding
problem on machines that evaluate double expressions in double
precision.  It is not necessary to convert w-TWO52[sx] to double
precision on return as implied in the comment in rev.1.3, since
the difference is exact.
This commit is contained in:
Bruce Evans 2005-12-03 07:38:35 +00:00
parent 7441377544
commit 3fc5a433e9
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=153043
1 changed files with 2 additions and 8 deletions
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10
lib/msun/src/s_rint.c
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@ -27,13 +27,7 @@ static char rcsid[] = "$FreeBSD$";
#include "math.h"
#include "math_private.h"
/*
* TWO23 is long double instead of double to avoid a bug in gcc. Without
* this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
* precision and doesn't clip them to double precision when they are
* assigned and returned.
*/
static const long double
static const double
TWO52[2]={
4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
@ -88,6 +82,6 @@ rint(double x)
if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
}
INSERT_WORDS(x,i0,i1);
w = TWO52[sx]+x;
*(volatile double *)&w = TWO52[sx]+x; /* clip any extra precision */
return w-TWO52[sx];
}