On 01/01/2013 12:36 PM, mfl...@racket-lang.org wrote:
07d5a9e Matthew Flatt <mfl...@racket-lang.org> 2013-01-01 12:31
:
| fix `expt' on small negative number and large positive odd
|
| The pow() function apparently gets it wrong on some platforms.
|
| Closes PR 13391
Thanks, Matthew. I'm looking forward to getting bugged by DrDr less. :D
One question about the fix:
src/racket/src/number.c
~~~~~~~~~~~~~~~~~~~~~~~
--- OLD/src/racket/src/number.c
+++ NEW/src/racket/src/number.c
@@ -2729,7 +2729,16 @@ static double sch_pow(double x, double y)
return scheme_infinity_val;
}
} else {
- return protected_pow(x, y);
+ double r;
+ r = protected_pow(x, y);
+ if ((r == 0.0) && !minus_zero_p(r)) {
+ /* check large odd power of a small negative number,
+ which some libraries get wrong for some reason */
+ if ((x < 0) && (fmod(y, 2.0) == 1.0)) {
+ r = scheme_floating_point_nzero;
+ }
+ }
+ return r;
}
}
#endif
I looked into fixing this myself, and identified this as a spot to
change. I also saw some JIT-looking stuff for `flexpt' that looked kind
of like it was machine code, so I didn't try to fix it. Does this code
you just changed get compiled during the build and then inlined by the JIT?
Neil ⊥
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